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- Large Volume Sample Introduction Using Temperature Programmable Injectors: Implications
of Liner Diameter.
H. Mol, Journal of High Resolution Chromatography,
Vol 18. (1995) 10-27
<< Read Abstract >>
Temperature programmable injectors with liner diameters ranging from 1 to 3.5 mm are evaluated and compared for solvent split injection of large volumes in capillary gas chromatography. The liner dimensions determine whether a large sample volume can be introduced rapidly or has to be introduced in a speed controlled manner. The effect of the injection technique used on the recovery of n-alkanes is evaluated. Furthermore the influence of the liner diameter on the occurrence of thermal degradation during splitless transfer to the analytical column is studied. Guidelines are given for the selection of the PTV liner internal diameter best suited for specific applications.
- Large Volume Injection in Capillary GC Using PTV Injectors: Comparison of Inertness of Packing Materials.
H. Mol, Journal of High Resolution Chromatography, Vol 18. (1995) 124-128
link to artical
- Recent improvements in high-temperature PTV injection for high-temperature capillary gas chromatography.
American M.P.M. van Lieshout, H.-G. Janssen and C.A. Cramers, Laboratory, August 1995, 38-44
- Simulated Distillation Using a Mid-Polarity Capillary Column.
Allen K. Vickers, Mike D'Amico and Phil Stremple, J&W Scientific, Pittcon '96 Presentation
- Characterization of Polymers by Multi-Step Thermal Desorption/Programmed Pyrolysis Gas
Chromatography Using a Hign Temperature PTV Injector.
M. van Lieshout, M.J.J. Hetem. Journal of High Resolution Chromatography, 19 (1996) 193-199
<< Read Abstract >>
Thermal treatment hyphenated with gas chromatography is a versatile and powerful tool in the study of polymer characterization. An inexpensive system where thermal treatment at different temperatures occurs inside a Programmable Temperature Vaporization injector (PTV) is described. The samples investigated, commercial plastics, are complex mixtures that contain several polymers and additives. These plastics as well as their pure constituents are subjected to multi-step thermal treatment. The individual chromatograms of the various constituents of the polymeric sample are correlated with those of the final material in order to identify additives (thermal desorption) and degradation products (pyrolysis). Results obtained with the new method indicate the interesting potentials of the technique for the characterization of polymer compositions. Reproducibility of absolute and relative peak areas has been considered and found to be acceptable. The absence of a heated transfer line and switching valves, which are always present in conventional set-ups, eliminates the risk of losses of high molecular weight components. Further advantages of the technique proposed are simplicity, versatility, and its inexpensive nature.
- Environmental Applications of Large Volume Injection in Capillary GC using PTV Injectors.
H.G.J. Mol, Journal of High Resolution Chromatography, Vol 19 (1996)69-79
<< Read Abstract >>
Temperature programmable (PTV) injectors with packed widebore (ca. 3.5 mm i.d.) liners are used for large volume injection in capillary gas chromatography with the aim to simplify and/or improve off-line sample pretreatment proecdures. A simple procedure for optimization of large volume PTV injection is described. The system performance, i.e. linearity and repeatability, is evaluated for polar nitrogen/phosphorus containing pesticides (PTV-GC-NPD) and organochlorine pesticides (PTV-GC-ECD) in river water extracts as well as for polycyclic aromatic hydrocarbons (PAHs) in river sediment (PTV-GC-MS).
- A Simplified Method for the Determination of Atmospheric Hydrocarbons.
K.D. Bartle and A.C. Lewis, LC-GC International (May 1996) 297-304
<< Read Abstract >>
An instrument has been developed for the automated in situ determination of airborne C1-C6 and C6-C12 volatile organic compounds using programmed temperature vaporisation (PTV) injection from a sorbent tube trap. A single sorbent tube placed as an injection port liner in a sub ambiently cooled PTV, can be repeatedly used to collect samples of air, with the trapped analytes being subsequently desorbed direct onto either a wide bore 100 % dimethyl polysiloxane (C6-C12) or porous layer Al2O3 Na2SO4 doped open tubular (C1-C6) gas chromatography column without use of intermediate cryogenic refocussing. High flow rates of helium used during the analysis result in not only a rapid and optimal separation, but also a fast recleaning of the sorbent tube making it ready to reuse following the analytical separation, with a lifetime of many hundreds of cycles.
Using 30 - 60 mesh activated charcoal as an adsorbent (C1-C6), breakthrough volumes of ethane were determined to be over 1 Litre. Desorption at 400 °C made the use of this type of trap for compounds as large as toluene possible. Using Tenax TA adsorbent (C6-C12), breakthrough volumes for most C6 compounds were found to be over 5 Litres, well in excess of the sample volume needed to quantify VOC concentrations in ambient air.
Detection was via parallel FID/ECD, with limits for individual compounds in a 1 Litre air sample of around 5-30 pptV dependant on detector response.
Methane cannot be quantifiably trapped onto activated charcoal, however owing to the high concentration of methane in the atmosphere (around 2 ppmV), a quantifiable response is observed on the chromatogram proportional to the internal volume of the injector port. This provides a new method for methane detection using existing equipment, which cannot be achieved when an intermediate cryofocusing step is used.
Examples of analysis of a wide range of both urban and rural ambient hydrocarbons are presented demonstrating the possibility to quasi-continuously monitor concentrations of VOCs in locations where high sensitivity continuous in situ analysis is required, but where cryogenic coolants may not be readily available or desirable.
- Large Volume Injection in Gas Chromatographic Trace Analysis Using Temperature Programmable (PTV) Injectors.
Hans G J Mol, Hans-Gerd Janssen, Carel A Cramers & Udo A Th Brinkman Trends in Analytical Chemistry, 15 4 (1996) 206-214
<< Read Abstract >>
The use of programmed-temperature vaporising (PTV) injectors for large-volume injection in capillary gas chromatography is briefly reviewed. The principles and optimisation of large-volume PTV injection are discussed. Guidelines are given for selection of the PTV conditions and injection mode for specific applications. Relevant examples from the recent scientific literature serve as illustrations.
- Atmospheric Monitoring of Volatile Organic Compounds Using Programmed Temperature Vaporisation Injection.
A.C. Lewis, P.W. Seakins, K. D. Bartle, Journal of High Resolution Chromatography 19 (1996) 686-690
<< Read Abstract >>
A method has been developed for the automated determination of C5-C10 and C2-C6 volatile organic compounds in urban and rural air, using programmed temperature vaporization injection from a sorbent tube trap. A single activated charcoal sorbent tube was repeatedly used to collect samples of air with trapped VOCs being subsequently desorbed onto either a wide bore dimethyl polysiloxane (C5-C10) or porous layer open tubular (C2-C6) gas chromatography column without use of intermediate cryogenic refocussing. The high flow rates of helium used during the analysis resulted in the sample tube being cleaned and ready to reuse following the analytical separation. Examples of analysis of aromatic VOCs in urban air, and biogenic emissions in rural air, collected in a Sitka Spruce forest are presented. Using this method it is possible to quasi-continuously monitor concentrations of VOCs in locations where high sensitivity in situ analysis is required, but where cryogenic coolants may not be readily available or desirable.
- Programmed-temperature vaporiser injector as a new analytical tool for combined thermal desorption-pyrolysis
of solid samples. Application to geochemical analysis.
M. van Lieshout, G.A. van den Bos, Journal of Chromatography A, 764 (1997) 73-84
<< Read Abstract >>
This paper describes a new analytical tool for the analysis of geological samples for geochemical purposes. A system is described that allows subsequent thermal treatment at several stages to occur inside the liner of a programmed temperature vaporiser injector (PTV). The samples under investigation are geological hydrocarbon source rock and coal samples. Analysis of the samples is performed in a sequential procedure. A three-step temperature-level procedure is proposed. The system described is inexpensive and easy to operate. The advantage of combining thermal desorption and pyrolysis sequentially inside a PTV injector is the flexibility of temperature selection, as well as the ease of calibration and quantitation. Moreover, the absence of a heated transfer line and heated valves minimises the risk of loss of high-molecular-mass compounds. The method described allows a detailed characterisation of oil and kerogen in a source rock. An atomic emission detector is used to monitor simultaneously the carbon and the sulphur signals for further structural elucidation of the kerogen. The results obtained with this system are in good agreement with those obtained with other pyrolysis systems.
- Quantitative Aspects of Comprehensive Two-Dimensional Gas Chromatography (GC6GC)
Jan Blomberg, Jan Beens, Hans Boelens, Robert Tijssen, J. High Resol. Chromatogr., Vol. 21, January 1998
<< Read Abstract >>
A software program was developed to enable the quantification of
the complex 3D-data sets as produced by GC6GC. Using this software, it was demonstrated that the detectability limit of GC6GC in
our study is 18 times better than that of ‘normal’ capillary gas chromatography (CGC). This enhancement is due to the signal increase
produced by the thermal modulation effect. The relative standard deviation of 0.9% as measured on a test mixture was excellent.
Furthermore, a comparison was made for the group-type separation of heavy gas oils between the hyphenation of LC and GC (LC-GC)
and GC6GC. Although these separations are different in nature, the agreement of the results of both methods was very good. The results
of GC6GC may even be more accurate, since, different from CGC, even in the most complex chromatograms the baseline in the second
dimension chromatograms is always present.
- Determination of triazine pesticedes in tap water by SPE-GC/MS
- Poster: Automated on-line SPE-GC/MS & GC/MS/MS for the analysis of drugs in equine urine.
Anachem
- Poster: Automated on-line SPE-GC/MS for the analysis of pesticide in Drinking Water.
Anachem
- A VISION to On-Line SPE-PTV-GC-MS Determination of Organic Micro Pollutants
in Surface Water.
Sjaak de Koning, Mark van Lieshout, Hans-Gerd Janssen, Wil van Egmond.
- Coupling devive for desorption of drugs from solid-phase extraction-pipette tips and on-line gas chromatographic analysis.
M.W.J. van Hout, R.A. de Zeeuw, G.J. de Jong, Journal of Chromatography A, 858 (1999) 117-122
<< Read Abstract >>
Solid-phase extraction-pipette tips were used for micro solid-phase extraction of lidocaine and diazepam. Off-line desorption was done after in-vial collection for reference purposes, whereas with on-line desorption the eluate was directly introduced in the gas chromatograph. With both methods the total eluate (100 µl) was introduced into the GC system, which was equipped with a programmed-temperature vaporiser (PTV) for large volume injection. For on-line desorption a laboratory-made coupling device was developed to connect the pipette tips with the injector of the PTV. The coupling device was applied successfully since no leakage occurred at the connection of the coupling device and the pipette tip. No significant differences in recovery of lidocaine and diazepam and in presence of impurities were observed between chromatograms obtained with either off-line or on-line desorption. Preliminary experiments with standard solutions showed recoveries of about 75% for a concentration level of 1 µg/ml. The system seems particularly suitable for high-throughput analysis.
- Programmable Temperature Vaporization interface for on-line trace-level enrichment - GC-MS of micropollutants in surface water.
Sjaak De Koning, Mark van Lieshout, Hans-Gerd Janssen, Udo A. Th. Brinkman. Journal of Microcolumn Separations, volume 12 issue 3, 2000. pages: 153-159
<< Read Abstract >>
In the present study, a fully automated solid-phase extraction (SPE) system, a programmed temperature vaporization (PTV) interface, and gas chromatography (GC) with mass spectrometric (MS) detection are combined for the trace-level analysis of micropollutants in surface water. The PTV interface is selected because of its reliability regarding large volume injection and its robustness when analyzing real-life samples. The mass spectrometer was used both in the full-scan and the selected ion monitoring modes and gave detection limits of about 15-40 ng/L and 0.7-5 ng/L (7.5-mL samples), respectively, for a series of NP-pesticides.
- Evaluation of the Programmed Temperature Vaporiser for Large Volume Injection of Biological Samples in Gas Chromatography.
M W J van Hout, R A de Zeeuw, J P Franke & G J de Jong. Journal of Chromatography B. 729 (1999) 199-210
<< Read Abstract >>
The use of a programmed temperature vaporiser (PTV) with a packed liner was evaluated for the injection of large volumes (up to 100 µl) of plasma extracts in a gas chromatograph. Solvent purity, which is essential when large volumes are injected into the GC system, was determined. Special attention was paid to the purity of the solvents used for the solid-phase extraction (SPE) procedure. For this SPE method, ethyl acetate was used as the extraction and reconstitution solvent, and thus the purity of the ethyl acetate was critical, especially when a non-selective GC detector was applied. The liquid capacity and inertness of different packed liners were investigated. The liner packed with ATAS “A” (modified Chromosorb-based material with special treatment) was found to be the most suitable for the analysis of the tested drugs. Good linearity in response for variations in volume and concentration was observed. A comparison was made between the applicability of flame ionisation detection (FID) and mass-selective detection (MSD). When 50-µl volumes of plasma extracts were injected with the PTV, the detection limits for secobarbital, lidocaine, phenobarbital and diazepam were about 50-times lower than when 1-µl volumes were injected. The detection limits of the tested compounds in plasma for injection of 50–100 µl plasma extract are 5–10 ng/ml for GC–FID whereas plasma concentrations of 250 pg/ml can be detected using the selected ion monitoring (SIM) mode of a MSD. For non-selective GC–FID, the background from a 50-µl injection was substantially larger than with 1-µl injection as a result of co-injected plasma matrix components and solvent impurities. These background effects were less with GC–MSD in the total ion current mode and virtually absent with GC–MSD in the SIM mode.
- On-line coupling of solid-phase extraction to gas chromatography with fast solvent vaporizing and concentration in an open injector liner. Analysis of pesticidus in equeous samples.
R. Sasano, T. Hamada, M.Kurano, M. Furuno. Journal of Chromatography A VOL. 896, 2000, 41-49
<< Read Abstract >>
The purpose of this study is to combine solid-phase extraction (SPE) with gas chromatography (GC) for the fully automated determination of pesticides and herbicides in aqueous samples. The interface technique employed for connecting SPE with GC was fast solvent vaporization and concentration in an open injector liner. The interface device consisted of the programmed-temperature vaporizing injector without using the packing material in the liner and the target compounds were concentrated around the inlet of the GC capillary column. This avoided the degradation of target compounds, and no precise control of the injecting speed was required, when an automatic SPE system was connected to GC–MS. The aqueous samples used in this system were prepared by spiking 29 kinds of pesticide and herbicide compounds, which are regulated by the Ministry of Health and Welfare of the Japanese National government, in purified water and river water, to a resulting concentration of 1 µg/l. Employing this system, the recoveries and RSDs (n=6) of most compounds were greater than 75% and within 10%, respectively. From the results of this study, we found that on-line automatic SPE and capillary GC–MS equipped with the fast solvent vaporizing and concentrating method in an open injector liner could be connected in order to obtain good results for the determination of pesticides in water samples.
- Direct injection of human plasma samples after ultrafiltration into programmed temperature vaporiser-gas chromatography–mass
spectrometry with packed liner.
Mohamed Abdel-Rehim, Karin A. Svensson, Yvonne Askemark, Karl-Johan Pettersson. Journal of Chromatography B, 755 (2001) 253–258
<< Read Abstract >>
The direct injection of plasma samples after ultrafiltration into a gas chromatograph using a packed injector liner was investigated. Ropivacaine, a local anaesthetic of the amide type and one of its metabolites (PPX) were used as model compounds in this evaluation. Phosphoric acid was added to the plasma to minimize the protein binding. After ultrafiltration, 50 µl of the sample was directly injected into the chromatographic system. No interfering peaks or damage to the GC or MS system were observed using ultrafiltration as a sample-preparation method. The validation of the method demonstrated good linearity and selectivity. The limits of quantification were 1.1 nM (301 pg/ml) and 1.4 nM (325 pg/ml) for ropivacaine and PPX, respectively. The liner had to be changed after 20 injections.
- Application of solid-phase extraction and rapid, large-volume injection for routine analysis of evironmental samples via U.S.
EPA SW-846 Method 8270D.
Daniel P.Dodson and Robert S. Johnson. American Laboratory News, April 2001
- Miniaturized automated matrix solid-phase dispersion extraction of pesticides in fruit
followed by gas chromatographic-mass spectrometric analysis.
E. Maria Kristenson, Esther G.J. Haverkate, Cees J. Slooten, Lourdes Ramos, René J.J. Vreuls, Udo A. Th. Brinkman. Journal of Chromatography A, 917 (2001) 277-286
<< Read Abstract >>
In this study a simple and fast miniaturized automated matrix solid-phase dispersion method for the sample preparation and quantitative extraction of pesticides was developed and evaluated. Only 25 mg of sample and 100 µl of organic solvent were used per analysis for this new miniaturized set-up. The extracts were subsequently analysed by GC–MS without any further purification. The method was optimized for oranges and tested for the determination of a variety of organophosphorus pesticides and a pyrethroid at concentration levels below the maximum residue levels set by the European Union and authorities in The Netherlands. The limits of detection were 4–90 µg/kg. The recoveries for pesticides in orange were 83–118% and the relative standard deviations for the total procedure were 10–13% (n=4) at the limit of quantification. The feasibility of the developed method for apple, pear and grapes was also studied. Equally good results were obtained, but for apple the washing step should be omitted.
- Use of a PTV injector to achieve inverse-large volume injection: injection of volatile analytes in a semi-volatile solvent.
Journal of Separation Science, 2001, 24, 291-296
<< Read Abstract >>
Large volume injection of volatile analytes in a semi-volatile solvent, termed inverse-LVI, has been accomplished using a programmable-temperature vaporizing (PTV) injector. It was found that simple optimization of the time the split valve remained closed allowed complete analyte transfer to the column, while venting most of the solvent. Increasing the PTV temperature ramp from 10 K/s to 15 K/s was found to improve peak shapes, especially of the early eluting peaks, by decreasing the injection bandwidth. In addition, the optimum splitless time was found to be independent of injection volume (up to solvent limits) meaning only a single optimization was necessary for quantitative analyte transfer from each solvent. The ability to quantitatively transfer the analyte to the column was also found to be solvent independent (propylene carbonate, tridecane, and Butyl CARBITOL® Solvent were evaluated). Excellent data were obtained for injection volumes up to 15 µL of propylene carbonate and 36 µL of tridecane using an unpacked fritted PTV liner.
- Automated determination of fatty acid methyl ester and cis/trans methyl ester composition of fats and oils.
Sjaak de Koning, Bram van der Meer, Geert Alkema, Hans-Gerd Janssen, Udo A.Th. Brinkman. Journal of Chromatography A, 922 (2001) 391-397
<< Read Abstract >>
The determination of the fatty acid composition (as methyl esters, FAMEs) of fats and oils and their cis/trans (CTME) distribution requires a simple, but manual and time-consuming sample preparation. The so-called BF3 method is often the preferred procedure. Because FAME/CTME analyses are encountered very frequently in the food industry, an automated, robot-based alternative is proposed which uses the sodium methylate procedure. After sample weighing and the (manual) addition of heptane (2 min), a XYZ robotic autosampler is used for all remaining work, which includes reagent addition, agitation, sample settling and the final injection into the gas chromatograph (10 min). The performance of the sodium methylate and BF3 methods are compared by analysing some 30 oil and fat samples. The novel procedure is much faster (less than 15 min versus ca. 1 h) and manual sample handling is drastically decreased. The experimental results obtained with the two methods frequently are the same, while small differences can be explained by (known) differences of the two methods in the conversion of minor oil/fat constituents, such as free fatty acids, wax esters and sterol esters. In case of FAME analyses, a hot injection is to be preferred over a cold injection. The RSDs of the peak areas were 1.5% for the major fatty acids to 11% for peaks that were just above the noise level. The detection limit were approximately 0.03%.
- Feasibility of the direct coupling of solid-phase extraction-pipette tips with a programmed-temperature vaporiser for gas chromatographic analysis of drugs in plasma.
M.W.J. van Hout, W.M.A. van Egmond, J.P. Franke, R.A. de Zeeuw, G.J. de Jong. Journal of Chromatography B, 766 (2002) 37-45
<< Read Abstract >>
Solid-phase extraction–pipette tips (SPE–PTs) were used for micro solid-phase extraction of lidocaine and diazepam from plasma. Off-line extraction was followed by on-line desorption. On-line desorption was carried out by direct coupling of the SPE–PTs with the liner of the programmed-temperature vaporiser. This coupling only required shortening of the liner by maximally 16 mm, cutting the SPE–PT, and equipping the remaining part with two O-rings. Due to the heating of the injector the SPE–PTs were heated as well, which resulted in a significant amount of impurities. Pre-heating and pre-washing was performed prior to the extraction to reduce the impurity level. The internal coupling device was applied successfully for the analysis of plasma samples with gas chromatography (GC) and mass-selective detection. Detection limits of 0.75 ng/ml and 2.5 ng/ml were obtained for lidocaine and diazepam, respectively, using 200 µl plasma. Recoveries for both compounds were about 80%. Although it is possible, the internal coupling device was not developed to be used as such. The main goal of this coupling was to show the feasibility of the integration of SPE–PTs with GC and to realize an important step to new automated SPE–GC systems.
- Pestizidanalytik in trauben mit LV-DTD/DMI-GC/TOF-MS.
LaborPraxis Dec. 2002.
(1.230kB)
- Analyses of the wood preservative component N-cyclohexyl- diazeniumdioxide in impregnated pine sapwood by direct thermal desorption-gas chromatography-mass spectrometry.
Jüngel, P.; De Koning, S.; Brinkman, U. A. T.; Melcher, E.: Journal of Chromatography A, Amsterdam 953 (2002) S. 199-205.
<< Read Abstract >>
Investigations concerning the qualitative and quantitative determination of the organic wood preservative component N-cyclohexyl-diazeniumdioxide (HDO) in treated timber were carried out by means of direct thermal desorption–gas chromatography–mass spectrometry (DTD–GC–MS). It could be shown that the identification of HDO in treated pine sapwood (Pinus sylvestris L.) is relatively simple using this analytical technique. Quantification of this active ingredient can be carried out using the peak area of the specific mass fragment m/z 114. A calibration curve with a high correlation coefficient was obtained in the range from 40 to 550 mg HDO per kg timber. Furthermore it can be deduced that the results obtained are characterised by an excellent reproducibility with standard deviations ranging from 5 to 10% in general. For the chosen experimental set up a detection limit of 4 mg HDO per kg treated pine sapwood was calculated, although merely 20% of the active ingredient was desorbed.
- Automated liner exchange - A novel approach in direct thermal desorption-gas chromatography.
De Koning, J.A.; Blokker, P.; Jüngel, P.; Alkema, G.; Brinkman U. A.T.: Chromatographia, Wiesbaden 56 (2002) S. 185-190.
<< Read Abstract >>
A system was developed for fully automated liner exchange in direct thermal desorption— gas chromatography— mass spectrometry (DTD-GC-MS). Samples are put into a newly developed liner which is capped with a standard crimp cap. The liners are placed in a sample tray and transported to the thermal desorption device. Both liner transport and liner exchange (which can be performed after each analysis) are automated. The system was tested for spores and pollen, vegetable oil, wood (preservative), car exhaust (BTEX), and tobacco (nicotine) analysis to demonstrate the robustness and flexibility of the approach.
- Trace-level determination of pesticides in food using difficult matrix introduction–gas chromatography–time-of-flight
mass spectrometry
Sjaak de Koning, Gunter Lach, Manfred Linkerhagner, Ralf Loscher, Peter Horst Tablack, Udo A. Th. Brinkman.
Journal of Chromatography A, 1008 (2003) 247–252
<< Read Abstract >>
A procedure for the fully automated analysis of food samples by means of difficult matrix introduction–gas chromatography–time-of-flight mass spectrometry (DMI–GC–ToF MS) is discussed. After extraction, samples require very little clean-up and are injected in a micro- or µ-vial which is held in a liner. Next, the liner is placed in the injector and the contents of the vial are thermally desorbed and led directly to the capillary GC column. After GC–ToF MS analysis, the data are processed automatically using a peak deconvolution algorithm. The practicability of the procedure was demonstrated by analysing spiked grape and pineapple samples down to the 1–10 ng/g concentration level.
- Analysis of pesticide residues in lettuce by large volume–difficult matrix introduction–gas chromatography–time of flight–mass spectrometry
(LV-DMI-GC-TOF-MS)
Katan Patel, Richard J. Fussell, David M. Goodallb and Brendan J. Keely Analyst, 2003, 128, 1228–1231
<< Read Abstract >>
A multi-residue method is described that eliminates the need for a clean-up step and thus allows the rapid determination of pesticides in crude extracts of lettuce. Samples were extracted with a mixture of ethyl acetate, Na2SO4 and NaHCO3 and the crude extracts analysed directly using large volume–difficult matrix introduction (LV-DMI) in combination with gas chromatography–time of flight–mass spectrometry (GC-TOF-MS). The LV-DMI procedure described was evaluated for the analysis of dimethoate, pyrimethanil, chlorothalonil, vinclozolin, furalaxyl and oxadixyl. Satisfactory response was obtained at the lowest calibrated level (LCL) of 0.0025 µg ml–1, with good linearity over the range 0.0025–0.5 µg ml–1(0.005–1.0 mg kg–1 equivalent). Average recoveries between 73 and 118% were obtained at the 0.01–0.5 mg kg–1 levels with RSD values 13%.
- AT-column, a novel concentrating technique for large-volume injections in gas chromatography
Sjaak de Koning, Mitsuhiro Kurano, Hans-Gerd Janssen, Udo A.Th. Brinkman. Journal of Chromatography A, 1023 (2004) 165–174
<< Read Abstract >>
Nowadays, large-volume injection is widely used for the GC determination of trace analytes, specifically to improve detectability. The most popular injectors for large-volume injections are the programmable temperature vaporisation (PTV) injector and the cold on-column (COC) injector, where each device has its own advantages and limitations. The novel AT-column concentrating technique combines features of two other injection techniques, loop-type large-volume and vapour overflow. AT-column injection is based on solvent evaporation in an empty liner with solvent vapour discharge via the split line. Little or no optimisation is required. The only relevant parameter is the injection temperature which can easily be calculated using the equation of Antoine. As an application, AT-column injection is combined with GC-MS for the trace-level determination of labile analytes and with GC-flame ionisation detection for the analysis of high molecular weight polymer additives. In summary, AT-column is an injection technique that combines the inertness of the COC, and the flexibility and robustness of the PTV large-volume technique.
- Automated on-line comprehensive two-dimensional LCxGC and LCxGC-ToF MS: Instrument design
and application to edible oil and fat analysis
Sjaak de Koning, Hans-Gerd Janssen, Marieke van Deursen, Udo A.Th. Brinkman. Journal of Separation Science 2004, 27, 397–409
<< Read Abstract >>
After a successful off-line feasibility study, the automation of comprehensively coupled liquid chromatography and gas chromatography (LC×GC) has been studied. Important aspects to consider when developing automated LG×GC include the relative speeds of the two dimensions, the compatibility of the LC eluent (type and flow rate) with the GC dimension, and the column loadabilities. Because the GC separation is relatively slow, the LC instrument has to be operated in the stop-flow mode. Two interfaces for transferring large numbers of subsequent LC fractions to the GC were constructed: one based on a six-port switching valve, and one which uses a dual side-port syringe. Both interfaces were found to perform fully acceptably. The actual transfer of the LC fraction to the GC was realised using a standard split injector to vaporise the compounds and LC eluent. Gas phase splitting was applied to match LC mass load and GC column loadability. The standard deviations of the peak areas obtained in this way were better than 7% (n = 6). The reliability of the system was demonstrated by the problem-free analysis of large series of oil and fat samples, with the focus on both intact triglycerides and their fatty acid methyl esters (FAMEs). Finally, the hyphenation of the automated LC×GC system to a sensitive and rapid-scanning time-of-flight mass spectrometer was realised. By using LC×GC-ToF MS, the information density of the chromatograms could be improved even further, which allowed easy identification of individual compounds as well as compound groups.
- On-line LC-GC and comprehensive two-dimensional LCxGC-ToF MS for the analysis of complex samples
Hans-Gerd Janssen, Sjaak de Koning, Udo A. Th. Brinkman. Anal Bioanal Chem (2004) 378 : 1944–1947
- New trend in sample preparation: on-line microextraction in packed syringe for liquid and gas chromatography applications
I. Determination of local anaesthetics in human plasma samples using gas chromatography-mass spectrometry
Mohamed Abdel-Rehim. Journal of Chromatography B, 801 (2004) 317–321
<< Read Abstract >>
A new technique for sample preparation on-line with LC and GC–MS assays was developed. Microextraction in a packed syringe (MEPS) is a new miniaturised, solid-phase extraction technique that can be connected on-line to GC or LC without any modifications. In MEPS approximately 1 mg of the solid packing material is inserted into a syringe (100–250 µl) as a plug. Sample preparation takes place on the packed bed. The bed can be coated to provide selective and suitable sampling conditions. The new method is very promising. It is very easy to use, fully automated, of low cost and rapid in comparison with previously used methods. This paper presents the development and validation of a method for microextraction in packed syringe MEPS on-line with GC–MS. Local anaesthetics in plasma samples were used as model substances. The method was validated and the standard curves were evaluated by the means of quadratic regression and weighted by inverse of the concentration: 1/x for the calibration range 5–2000 nM. The applied polymer could be used more than 100 times before the syringe was discarded. The extraction recovery was between 60 and 90%. The results showed close correlation coefficients (R>0.99) for all analytes in the calibration range studied. The accuracy of MEPS–GC–MS was between 99 and 115% and the inter-day precision (n=3 days), expressed as the relative standard deviation (R.S.D.%), was 3–10%.
- Evaluation of large volume-difficult matrix introduction-gas chromatography-time of flight-mass spectrometry (LV-DMI-GC-TOF-MS) for the
determination of pesticides in fruit-based baby foods
K. Patel, R. J. Fussell, D. M. Goodall and B. J. Keely, Food Additives and Contaminants, Vol. 21, No. 7 (July 2004), pp. 658–669
<< Read Abstract >>
The European Union Baby Food Directive (1999/39/EC), which came into force on 1 July 2002, set legal maximum residue levels at 0.01 mg kg-1 for all pesticides in baby foods. The combination of large volume-difficult matrix introduction (LV-DMI) with gas chromatography-time of flight-mass spectrometry (GC-TOF-MS), described herein, provides the analyst with a simple but rapid alternative GC-MS technique for the multiresidue analysis of pesticides in fruit-based baby foods. Samples were extracted with ethyl acetate in the presence of Na2SO4 and NaHCO3 and the crude extracts were analysed directly using LV-DMI-GC-TOF-MS. The best overall results (98 pesticides quantified satisfactorily at a spiking level of 0.01 mg kg-1) were obtained by analysis of concentrated extracts (2.5 g crop ml-1) using a 30-m column, with a chromatographic run time of 25 min. A good signal-to-noise ratio was obtained at the lowest calibrated level (0.0125 µg ml-1), with excellent linearity achieved over the range 0.0125-0.25 µg ml-1 (equivalent to 0.005-0.1 mg kg-1). Average recoveries for the analysis of five replicate determinations at a spiking level of 0.01 mg kg-1 were between 79 and 114% with relative standard derivations generally less than 20%.
- Development of a Method for Dioxin Analysis of Small Serum Samples with Reduced Risk of Volatilization
Kimiyoshi Kitamura, Yoshikatsu Takazawa, Yoshiyuki Takei, Xiaojing Zhou, Shunji Hashimoto, Jae-Won Choi, Hiroyasu Ito, and Masatoshi Morita
Anal. Chem. 2005, 77, 1727-1733
<< Read Abstract >>
To analyze the dioxin content of samples, including dibenzo-p-dioxins/dibenzofurans, and coplanar polychlorinated biphenyls (Co-PCBs), a large volume is usually necessary. This is difficult, however, when analyzing clinical samples, such as serum and tissue. We therefore sought to increase the sensitivity of high-resolution gas chromatography/high-resolution mass spectrometry (HRGC/HRMS) in analyzing dioxins by injecting most of the extract from a small clinical sample. The concentration of each congener was estimated by injecting extracts of 5-g samples into a gas chromatography capillary precolumn (AT column) and by assaying extracts of 25-g samples by conventional splitless methods. We found that the limit of detection with the AT column was lower than that obtained by the splitless technique. In the AT column technique, 100 µL of the 110-µL final solution, equivalent to 4.5 g of the original sample, was injected into HRGC/HRMS. In contrast, 2 µL of the 20-µL final solution, equivalent to 2.5 g of original sample, was assayed using the splitless method. Moreover, when 25 fg of ultratrace dioxin was added to 100 µL of HRGC/HRMS sample and injected into the AT column, the peak area was almost the same as that obtained with 2 µL of HRGC/HRMS sample injected using the splitless method. Although assaying 10-20 µL of sample by the splitless method presents difficulties due to sample volatility, this problem can be reduced by using volumes larger than 100 µL. We tested this application by quantifying the parts-per-trillion levels, on a lipid weight basis, of each congener in a serum sample of 5 g using the AT column HRGC/HRMS method. We found this application to be successful and practical for mass screening of dioxin exposure in clinical samples.
- Use of automated direct sample introduction with analyte protectants in the GC–MS analysis of pesticide residues
Tomas Èajka, Kateøina Mastovska, Steven J. Lehotay, Jana Hajslova. J. Sep. Sci. 2005, 28, 1048–1060
<< Read Abstract >>
Automated large-volume direct sample introduction, or difficult matrix introduction (DMI), was investigated in the determination of 44 pesticide residues possessing a wide range of physico-chemical properties (volatility, polarity, pK(a)) in fruit-based baby food by means of gas chromatography-mass spectrometry (GC-MS) with a quadrupole mass analyzer. DMI has advantages over traditional injection because large volumes (up to 30 microL) of potentially dirty sample extracts can be injected into the GC-MS, but nonvolatile matrix components that would normally contaminate the inlet are removed after every injection. The extra matrix and glass surfaces involved in DMI, however, make the system more prone to the matrix-induced chromatographic enhancement effect, which adversely affects quantification of several pesticides. To overcome this problem, matrix-matched calibration standards and/or the use of analyte protectants were applied in the DMI approach, and the analysis of extracts was also compared before and after undergoing clean-up by dispersive solid-phase extraction. For best quantification, clean-up was still needed, and the combination of matrix-matching with analyte protectants gave the most reproducible results. Depending on the application, however, the addition of analyte protectants (a mixture of 3-ethoxy-1,2-propanediol, L-gulonic acid 3-lactone, and D-sorbitol) to sample extracts and calibration standards in solvent (non-matrix matched), gave satisfactory quantification for most of the 44 pesticides tested. The lowest calibration levels for 34 of the 44 pesticides were < or = 10 ng/g, which meets the standard required by the European Union Baby Food Directive (2003/13/EC).
- Miniaturised pressurised liquid extraction of polycyclic aromatic hydrocarbons from soil and sediment with subsequent large-volume
injection–gas chromatography
L. Ramos, J.J. Vreuls, U.A.Th. Brinkman. Journal of Chromatography A, 891 (2000) 275–286
<< Read Abstract >>
Analyte extraction is the main limitation when developing at-line, or on-line, procedures for the preparation of (semi)solid environmental samples. Pressurised liquid extraction (PLE) is an analyte- and matrix-independent technique which provides cleaner extracts than the time-consuming classical procedures. In the study, the practicality of miniaturised PLE performed in a stainless-steel cell, and combined with subsequent large-volume injection (LVI)–GC–MS was studied. As an example, the new system was applied to the determination of polycyclic aromatic hydrocarbons (PAHs) in soils and a sediment. Variables affecting the PLE efficiency, such as pressure and temperature of the extraction solvent and total solvent volume, were studied. Toluene was selected as extraction solvent and a total solvent volume of 100 µl was used for the 10 min static-dynamic PLE of 50-mg samples. Additional clean-up or filtration of the sample extracts was not required. Detection limits using LVI–GC–MS were below 9 ng/g soil for the 13 PAHs more volatile than indeno[1,2,3-cd]pyrene in real soil samples and the repeatability of the complete PLE plus LVI–GC–MS method for the analysis of the endogenous PAH was better than 15%. Comparison of PLE and Soxhlet or liquid-partitioning extraction results for the analysis of non-spiked samples showed that the efficiency of PLE is the same or better than for the other two extraction methods assayed.
- Miniaturised pressurised liquid extraction of chloroanilines from soil with subsequent analysis by large-volume injection–gas
chromatography–mass spectrometry
E. Maria Kristenson, Silvia Angioi, Rene J.J. Vreuls, Maria Carla Gennaro, Udo A.Th. Brinkman. Journal of Chromatography A, 1058 (2004) 243–249
<< Read Abstract >>
A number of chloroanilines were extracted from soil by means of miniaturised pressurised liquid extraction (PLE). The extraction procedure was optimised for both large-volume on-column (LV-OC) and programmed-temperature vaporisation (PTV) injections combined with GC–MS. Hexane was the only extraction solvent suited for LV-OC and hexane/acetone gave the best results when using a PTV. Overall, the hexane/acetone-plus-PTV procedure shows better results than the hexane-plus-LV-OC method in terms of analyte recovery (36–109% versus 5–87%), repeatability (8–13% versus 4–31%) and detection limits. Both approaches allow detection of the chloroanilines in complex soil samples down to the 5–50 ng/g range. However, the PTV-based procedure is superior as regards robustness: over one hundred samples can be analysed without any maintenance being required.
- Automated DMI for screening of cosmetic products
Erwin Kaal, Hans-Gerd Janssen, University ofAmsterdam and Mitsuhiro Kurano, ATAS GL International Shimadzu News, 1/2006 page 6-8.
- Application of direct thermal desorption gas chromatography and comprehensive twodimensional
gas chromatography coupled to time of flight mass spectrometry for analysis of organic compounds in ambient aerosol particles
Jurgen Schnelle-Kreis, Werner Welthagen, Martin Sklorz, Ralf Zimmermann. J. Sep. Sci. 2005, 28, 1648–1657
<< Read Abstract >>
Semivolatile organic compounds (SVOC) associated with ambient particles smaller than 2.5 m (PM2.5) were determined in the city of Augsburg, Germany. Daily samples were collected at a central monitoring station from late summer 2002 to spring 2005. SVOC were analysed by direct thermal desorption (DTD)-GC and comprehensive 2-D GC coupled to TOF MS (DTD-GC-TOF MS and DTD-GC×GC-TOF MS). Two hundred compounds were quantified and semi-quantified on a daily basis by DTD-GC-TOF MS. n-Alkanes, n-alkan-2-ones, n-alkanoic acid methyl esters, acetic acid esters, n-alkanoic acid amides, nitriles, linear alkylbenzenes and 2-alkyl-toluenes, hopanes, PAH, alkylated PAH and oxidised PAH, and several compounds that are not grouped in homologous rows or compound classes were determined. Changes in concentration and pattern of several target compounds as well as methodological advantages and restrictions of DTD-GC-TOF MS are briefly discussed. DTD-GC-TOF MS analysis provided data particularly suited for source receptor modelling and epidemiological time series studies on the health effects of ambient PM. GC×GC enhances chromatographic resolution of PM samples and therefore amplifies the peak identification capabilities of the TOF MS.
- Analysis of particle-associated semi-volatile aromatic and aliphatic hydrocarbons in urban particulate matter on a daily basis
Jurgen Schnelle-Kreis, Martin Sklorz, Anette Peters,Josef Cyrysb, Ralf Zimmermann. Atmospheric Environment 39 (2005) 7702–7714.
<< Read Abstract >>
PM2.5 Particle-associated semi-volatile organic compounds (SVOC) were determined in the city of Augsburg, Germany. Daily samples were collected at a central monitoring station from late summer to late autumn 2002. The concentrations of polycyclic aromatic hydrocarbons (PAH), oxidized PAH (O-PAH), n-alkanes, hopanes and long chain linear alkylbenzenes were determined by direct thermal desorption-gas chromatography-time of flight mass spectrometry (DTD-GC-TOFMS). Additionally, PM2.5 particle mass and number concentrations were measured. The sampling campaign can be divided into two parts, distinguished by a lower temperature level in the second part of the campaign. The particulate mass concentration showed no significant changes, whereas most of the SVOC had significant higher mean and peak concentrations in the colder period. The analysis of the data showed an increased influence of non-traffic sources in the colder period, reflected by a weak shift in the PAH profile and a significant shift in the hopane pattern. Statistical analysis of the inter-group correlations was carried out. Eight clusters partly representing different sources of the aerosol have been identified.
- Ultratraces analysis of organochlorine pesticides in drinking water by solid phase extraction coupled with large volume injection/gas chromatography/
mass spectrometry
Silvia H. G. Brondi Fernanda C. Spoljaric Fernando M. Lancas. J. Sep. Sci. 2005, 28, 2243–2246.
<< Read Abstract >>
This study describes an SPE coupled with large volume injection (LVI) analytical method for the analysis of organochlorine pesticides, BHC ( ,  ,  ), aldrin, endosulfan (, ), endrin, dieldrin, and DDT, from aqueous samples. Determination was carried out by GC with MS. The LODs of organochlorine pesticides were determined at 10 ng/L concentration levels, and the results show that SPE-LVI-GC/MS has the potential to accurately determine organochlorine pesticides in water, as it avoids analyte classes in the various steps of a typical extraction procedure.
- Organische Verbindungen in Feinstaub (German language)
Nachrichten aus der Chemie, 54, Juni 2006, 676
- On-line size exclusion chromatography–pyrolysis-gas chromatography–mass spectrometry for copolymer
characterization and additive analysis
Erwin R. Kaal, Geert Alkema, Mitsuhiro Kurano, Margit Geissler, Hans-Gerd Janssen. Journal of Chromatography A, 1143 (2007) 182–189.
<< Read Abstract >>
On-line coupled size exclusion chromatography–pyrolysis gas chromatography mass spectrometry (SEC–Py-GC–MS) is studied as a novel tool for the characterization of complex polymer samples. An automated system for on-line SEC–Py-GC–MS allowing transfer of multiple fractions was developed based on stop-flow operation of the SEC dimension, syringe-based transfer of the SEC fraction to the GC instrument and solvent elimination with subsequent pyrolysis in a programmed temperature vaporization (PTV) injector. After optimization the system was applied to the characterization of a complex terpolymer composed of very similar monomers. The use of the system for combined pyrolysis and additive analyses in polycarbonate was also demonstrated. Results obtained with the new method indicate the interesting potentials of the method for detailed characterization of polymeric materials.
- Evaluation of the QuEChERS sample preparation approach for the analysis of pesticide residues in olives
Sara C. Cunha, Steven J. Lehotay, Katerina Mastovska, Jos. O. Fernandes,Maria Beatriz, P. P. Oliveira. J. Sep. Sci. 2007, 30, 620 – 632.
<< Read Abstract >>
This paper describes the use of a quick, easy, cheap, effective, rugged, and safe (QuEChERS) method for extraction and cleanup of 16 pesticide residues of interest in olives and olive oil. These products contain a high lipid content, which can adversely affect pesticide recoveries and harm traditional chromatographic systems. For extraction, the main factors (oil and water content) were studied and optimized in experiments to maximize pesticide recoveries. Dispersive SPE with different sorbents was also investigated to minimize matrix coextractives and interferences. For analysis, a new automated DSI device was tested in GC-MS to avoid nonvolatile coextractives from contaminating the instrument. LC-MS/MS with positive ESI was used for those pesticides that were difficult to detect by GC-MS. The final method was validated for olives in terms of recoveries, repeatabilities, and reproducibilities using both detection techniques. The results demonstrated that the method achieved acceptable quantitative recoveries of 70-109% with RSDs <20% for DSI-GC-MS and 88-130% with RSDs <10% for LC-MS/MS, and LOQ at or below the regulatory maximum residue limits for the pesticides were achieved.
- Automation of the GM-MS analysis of mineral oil contaminations in water
O. Lerch, P. Zinn, H.J. Götze. Fresenius J. Anal. Chem. (2000) 267 : 195-200.
- On-line SEC-Py-GC-MS for the Automated Comprehensive Characterization of Copolymers (coupling matters)
Erwin R. Kaal, Mitsuhiro Kurano, Margit Geißer, Peter schoenmakers and Hans-Gerd Janssen. LC·GC Europe September 2007, 444-452 (coupling matters).
<< Read Abstract >>
Size-exclusion chromatography (SEC) and pyrolysis-gas chromatography (Py-GC) are commonly used to characterize copolymers. SEC is a powerful method to determine the molecular-weight distribution of polymers whereas Py-GC provides valuable information on their chemical composition. The combination of these two techniques could yield combined size and composition information for copolymers or polymer mixtures. A fully automated system was constructed to perform these two-dimensional (2D) characterizations. Several examples of the use of this new technique to comprehensively characterize polymers are described.
- Automated GC-MS analysis of raw biological samples. Application to fatty acid profiling of aquatic micro-organisms.
Akoto L., Pel R.,Brinkman U., Vreuls R.J.J. J. Anal. Appl. Pyrol., 73, (2005) 69-75
<< Read Abstract >>
A direct thermal desorption (DTD) interface was applied to profile the fatty acid composition of whole/intact aquatic micro-organisms using trimethylsulfonium hydroxide (TMSH) as derivatization reagent in a fully automated fashion without any sample treatment.
DTD was used to release cellular free and esterified fatty acids, after conversion into their methyl esters, from the very limited amounts of cells available in plankton community analysis using fluorescence-activated cell sorting of mixed (natural) microbial/algal populations. The liner of the GC injector is used as a sample-and-reaction container with the aid of the DTD interface. The fatty acids are converted into their methyl esters after an incubation (hydrolysis) time of 30 min with TMSH. After transportation into the injector, the liner is heated to effect thermally assisted methylation. Simultaneously, the fatty acid methyl esters (FAMEs) are introduced from the liner into the capillary GC column.
On the basis of peak intensities, the fatty acid compositions, thus obtained, were shown to be closely similar to those of a conventional lipid extraction and methylation procedure.
The method was applied to some common freshwater algae, the green algae Scenedesmus acutus, the diatom Asterionella formosa and the filamentous cyanobacterium, Limnothrix sp. strain MRI. Using this novel method, poly-unsaturated fatty acids were methylated into their corresponding methyl esters without isomerization/pyrolytic side-reactions.
The present method has been used to perform large series of analyses of algal and microbial cells. Up to 18 samples could be analysed per day. In order to reach this sample throughput, preparation of the (n + 1)th sample was performed simultaneously with GC analysis of the nth sample.
- At-line gas chromatographic-mass spectrometric analysis of fatty acid profiles of green microalgae using drect thermal desorption interface.
P. Blokker, R. Pel, L. Akoto, U.A.T. Brinkman, R.J.J. Vreuls. J. Chromatogr. A 959 (2002) 191-201.
<< Read Abstract >>
Thermally assisted hydrolysis and methylation–gas chromatography (THM–GC) is an important tool to analyse fatty acid in complex matrices. Since THM–GC has major drawbacks such as isomerisation when applied to fatty acids in natural matrices, a direct thermal desorption (DTD) interface and an incubation time of 30 min were used to circumvent these problems. Using vegetable oils such as sunflower oil and triarachidonin, the conversion of triglycerides into their fatty acid methyl esters (FAMEs) was investigated. The yields using a DTD (and trimethylsulfonium hydroxide as a reagent) were found to be similar or even higher than when applying a conventional off-line method, while the FAME profiles were identical. When the procedure was applied to analyse the FAME profiles of microbial cells in a methanolic or aqueous suspension, it was found that accurate profiles are obtained for such samples. Thus, the present approach opens the route to analyse fatty acids in microbial cells in a fully automated fashion, which will allow high sample throughput.
- Characterization of olive oil volatiles by multi-step direct thermal desorption–comprehensive gas chromatography–time-of-flight mass
spectrometry using a programmed temperature vaporizing injector
Sjaak de Koning, Erwin Kaal, Hans-Gerd Janssen, Chris van Platerink, Udo A.Th. Brinkman article in press as: S. de Koning et al., Journal of Chromatography A, 1186 (2008) 228–235.
<< Read Abstract >>
The feasibility of a versatile system for multi-step direct thermal desorption (DTD) coupled to comprehensive gas chromatography (GC x GC)with time-of-flight mass spectrometric (TOF-MS) detection is studied. As an application the system is used for the characterization of fresh versus
aged olive oil after treatment at 70, 175, 250 and 600°C.
- Determination of the carbon isotopic composition of whole/intact biological specimens using at-line direct thermal desorption to effect thermally assisted hydrolysis/methylation.
Akoto L, Vreuls RJ, Irth H, et al. J Chromatogr A 2007 Sep 11.
<< Read Abstract >>
In this paper, we discuss the use of a direct thermal desorption (DTD) interface as an alternative to Curie-point flash pyrolysis system as an inlet technique in gas chromatography-combustion isotope-ratio mass spectrometry (GC/C-IRMS) analysis of whole/intact phytoplankton and zooplankton specimens. The DTD in combination with a combipal auto-injector is programmed to perform the injection, evaporation of solvents, transport of capped programmed-temperature vaporizer (PTV) liners to the PTV injector and chemical derivatisation (thermally assisted hydrolysis/methylation; THM) such that a profile of a cellular fatty acids is obtained. Flow-cytometric sorted microalgae and handpicked zooplankton are used as samples with trimethylsulfonium hydroxide (TMSH) as methylating reagent. A major advantage of this novel approach over the Curie-point technique is the automation of the total procedure, which allows unattended analysis of large sample series. The profiles and delta(13)C carbon isotopic signatures of the fatty acid methyl esters (FAMEs) produced are very similar to those obtained using the Curie-point flash pyrolysis method. It is shown that algal samples must be kept no longer than 48h in the DTD sample tray prior to the THM-analysis in order to maintain the integrity of their FAME profile.
- Fatty acid profiling of raw human plasma and whole blood using direct thermal desorption combined with gas chromatography-mass spectrometry.
Akoto L, Vreuls RJ, Irth H, et al. J Chromatogr A 2007 Sep 11.
<< Read Abstract >>
Gas chromatography (GC) has in recent times become an important tool for the fatty acid profiling of human blood and plasma. An at-line procedure used in the fatty acid profiling of whole/intact aquatic micro-organisms without any sample preparation was adapted for this work. A direct thermal desorption (DTD) interface was used to profile the fatty acid composition of human plasma and whole human blood of eight volunteers in a procedure omitting the usual lipid extraction steps that precede sample methylation in the traditional (off-line) protocols. Trimethylsulfonium hydroxide (TMSH) was used as reagent for thermally assisted methylation. In a fully automated manner, the liner of the GC injector is used as a sample-and-reaction container with the aid of the DTD interface. The fatty acid methyl ester (FAME) profiles obtained using this novel approach, were very identical to those obtained when the traditional off-line protocol was applied. FAME yields obtained in the at-line DTD method were found to be very similar for saturated fatty acids, but significantly higher for polyunsaturated fatty acids compared to off-line yields. As a result of the contribution of circulating cell membranes in blood, substantial differences were observed when the amount of FAMEs obtained in whole human blood and human plasma samples were compared after their analysis. Thanks to the fully automated operation of this novel procedure, large series of analyses can easily be performed.
- Hyphenation of aqueous liquid chromatography to pyrolysis-gas chromatography and mass spectrometry for the comprehensive
characterization of water-soluble polymers.
Erwin R. Kaal, Mitsuhiro Kurano, Margit Geißler, Hans-Gerd Janssen. Journal of Chromatography A, Volume 1186, Issues 1-2, 4 April 2008, Pages 222-227.
<< Read Abstract >>
A recently developed hyphenated system for “organic” size-exclusion chromatography–pyrolysis-gas chromatography–mass spectrometry
(SEC–Py-GC–MS) is adapted to allow the use of aqueous LC eluents as applied in the characterization of water-soluble polymers. The system uses
syringe-based transfer of multiple LC-fractions to the GC instrument with solvent elimination and subsequent pyrolysis in a programmed temperature
vaporization injector. The problems of the large-volume injections of aqueous, salt containing eluents into the Py-GC–MS are solved by using
a ‘sintered-bed liner’ for elimination of the water at a high temperature, a volatile salt and the installation of a back-flush option. After optimization,
the system was applied for the determination of the combined molecular weight–chemical composition of a polyethylene glycol–polypropylene
glycol block copolymer. This analysis was done with the system in the aqueous SEC–Py-GC–MS mode. Also demonstrated is the automated at-line
characterization of a random polystyrene–polymethylmethacrylate copolymer, now with the system in the gradient reversed-phase LC–Py-GC–MS
mode. The methods proposed in the present work are very useful for the detailed characterization of water-soluble copolymers.
- Method Development and Application of Compound-Specific Isotope Analysis for Source Allocation of Polycyclic Aromatic
Hydrocarbons in Contaminated Soil.
MASTER THESIS of Flor Toledo Rodríguez, University Tübingen
<< Read Abstract >>
This investigation focuses on the application of compound-specific isotope analysis (CSIA) of carbon,
a highly powerful and less known analytical technology, in order to assess the PAHs source allocation
at a site with a massive and highly diverse contamination. With this method, the assessment of the
carbon isotope ratios of PAHs can be used as source indicator at highly contaminated sites.
The objective of this master thesis was to develop an extraction and purification method to isolate the
PAHs from a complex contaminated soil matrix. Of special interest was to determine if the extraction
and purification procedures affect the isotopic composition of the target analytes. This was of big
importance since the main aim was the evaluation of the real isotopic composition of PAHs at the
contaminated site. In order to achieve this objective, two enrichment and purification methods for the
PAHs in the soil matrix were developed. The first method consisted of a liquid-solid extraction
combined with a liquid-liquid extraction and a flash chromatography (LSE/LLE/FC), and the second
method consisted of an accelerated solvent extraction combined with a liquid-liquid extraction and a
final flash chromatography (ASE/LLE/FC). The comparison of the separated PAHs through these
methods with respect to PAH standards showed that no detectable change in the isotopic composition
of the target compounds occurred and therefore these purification methods can effectively be applied
in highly PAH contaminated soil samples at the surveyed site through CSIA if soil samples contain a
minimum concentration of PAHs of 11.1 mg/kg.
download the thesis.
- Rapid analysis of multiple pesticide residues in fruit-based baby food using programmed temperature vaporiser injection–low-pressure gas
chromatography–high-resolution time-of-flight mass spectrometry
Tomas Cajka, Jana Hajslova, Ondrej Lacina, Katerina Mastovska, Steven J. Lehotay Journal of Chromatography A, 1186 (2008) 281–294
<< Read Abstract >>
A rapid method using programmed temperature vaporiser injection-low-pressure gas chromatography-high-resolution time-of-flight mass spectrometry (PTV-LP-GC-HR-TOF-MS) for the analysis of multiple pesticide residues in fruit-based baby food was developed. The fast and
inexpensive buffered QuEChERS (quick, easy, cheap, effective, rugged, and safe) extraction method and "conventional" approach that employs
ethyl acetate extraction followed by gel permeation chromatography (GPC) cleanup were employed for sample preparation. A PTV injector in
solvent venting mode was used to reduce volume of acetonitrile and acetic acid (from the buffered QuEChERS extracts) that caused higher column
bleed without their elimination. Otherwise, the time-to-digital converter would become saturated in HR-TOF-MS. For fast GC separation allowing
analysis of 100 analytes within a 7 min runtime, both a high temperature programming rate and vacuum conditions in a megabore GC column
were employed. The use of HR-TOF-MS allowed the unbiased identification and reliable quantification of target analytes through the application
of a narrow mass window (0.02 Da) for extracting analyte ions and the availability of full spectral information even at very low levels. With only
a few exceptions, the lowest calibration levels for the pesticides tested were .0.01 mg/kg for both sample preparation methods, which meets the
EU maximum residue limit set for pesticide residues in cereal-based foods and baby foods (2003/13/EC).
- Extending the molecular application range of gas chromatography
Erwin Kaal, Hans-Gerd Janssen Journal of Chromatography A, 1184 (2008) 43–60.
<< Read Abstract >>
Gas chromatography is an important analytical technique for qualitative and quantitative analysis in a wide range of application areas. It is fast,
provides a high peak capacity, is sensitive and allows combination with a wide range of selective detection methods including mass spectrometry.
However, the application area of GC is limited because the molecules to be analysed have to be thermally stable and sufficiently volatile. Numerous
molecules do not meet these requirements and hence are not amenable to direct GC analysis. Recent research has resulted in better chromatographic
columns and methods for sample preparation that enable a significant expansion of the molecular application range of GC. The strategies exploited
include conversion of (macro)molecules into smaller species and approaches to reduce the polarity of molecules. In this review we identify four
generic routes for extending the applicability of GC. These include high-temperature GC, derivatisation, pyrolysis and thermochemolysis. The
principles, recent developments and future perspectives of these routes are discussed and examples of applications using the different options
will be shown. Life sciences, metabonomics and profiling strategies for sample characterization are identified as important future drivers for the
continued development of GC.
- Two-dimensional Characterization of (Bio-)macromolecules using LC-Py-GC-MS
Erwin R. Kaal, Hans-Gerd Janssen. GIT Spezial . Separation 1/2008. page 20-22.
<< Read Abstract >>
Unlike single compounds, polymers consist of many different molecules.
These molecules are derived from the same building blocks, but diier in chain length, end-group, degree of branching, etc. For a true understanding of a
polymer and its properties detailed knowledge of all features is necessary. Here it is generally not sufficient to just know the average distribution
of isolated single parameters such as the molecular weight distribution or the average composition of the polymer. Multi-dimensional information
is needed, giving for example copolymer composition as a function of molecular weight. Hyphenated combinations of a liquid chromatographic separation
and pyrolysis GC provide an ideal means of deriving such information, as will be shown below.
- Fully automated system for the gas chromatographic characterization of polar
biopolymers based on thermally assisted hydrolysis and methylation
Erwin Kaal, Sjaak de Koning, Stella Brudin, Hans-Gerd Janssen Journal of Chromatography A, 1201 (2008) 169–175.
<< Read Abstract >>
Pyrolysis-gas chromatography (Py-GC) is a powerful tool for the detailed compositional analysis of polymers.
A major problem of Py-GC is that polar (bio)polymers yield polar pyrolyzates which are not easily
accessible to further GC characterization. In the present work, a newly developed fully automated procedure
for thermally assisted hydrolysis and methylation (THM) of biopolymers is described. Drying of the
sample, addition of the reagent, incubation and pyrolysis are performed inside the liner of a programmable
temperature vaporizer injector. The newsystemnot only allows efficient analysis of large series ofsamples,
but also allows automated optimization of the experimental parameters based on an experimental design
approach. The performance of the automated THM-procedurewas evaluated by performing THM–GC of a
poly(acrylic acid)–poly(maleic anhydride) copolymer (PAA/PMAH) and several polysaccharides. The optimized
THM-procedurewas applied for the structural characterization and differentiation of several lignins
and hydroxypropylmethyl-celluloses. It was also applied to proteins. Here myoglobin and cytochrome c
were used as the model compounds. Both conventional GC–mass spectrometry (MS) and comprehensive
two-dimensional gas chromatography (GC×GC)–time-of-flight (TOF) MS were used for separation and
identification of the species formed. The information obtained can aid in structure elucidation of polar
biopolymers aswell as in providing detailed compositional information which can be used to differentiate
structurally similar biopolymers.
- Comparison of Natural and Artificial Aging of Ballpoint Inks
Claudia Berger-Karin, Ursula Hendriks, Jochen Geyer-Lippmann. J Forensic Sci, July 2008, Vol. 53, No. 4.
<< Read Abstract >>
Solvent evaporation caused by aging from ballpoint inks was measured by gas chromatography . mass spectroscopy (GC .MS). The
sample preparation was carried out with two different thermal desorption systems. The results are compared. Thirteen inks were classified with regard
to their solvents, polymers, and additives. The variation of the aforementioned compounds caused by aging was monitored for naturally and artificially
aged samples. In this paper, the results are compared and discussed with respect to forensic casework.
- A fast method for the identification of Mycobacterium tuberculosis in sputum
and cultures based on thermally assisted hydrolysis and methylation
followed by gas chromatography–mass spectrometry
Erwin Kaal, Arend H.J. Kolk, Sjoukje Kuijper, Hans-Gerd Janssen. Journal of Chromatography A, 1216 (2009) 6319–6325
<< Read Abstract >>
A fast gas chromatography–mass spectrometry (GC–MS) method with minimum sample preparation is
described for early diagnosis of tuberculosis (TB). The automated procedure is based on the injection of
sputum samples which are thenmethylated inside the GC injector using thermally assisted hydrolysis and
methylation (THM). The THM–GC–MS procedure was optimized for the injection of sputum samples. For
the identification of Mycobacterium tuberculosis the knownmarker tuberculostearic acid (TBSA) and other
potential markers were evaluated. Hexacosanoic acid in combination with TBSA was found to be specific
for the presence of M. tuberculosis. For validation of the method several sputum samples with different
viscosities spiked with bacterial cultures were analyzed. Finally, 18 stored sputum samples collected in
Vietnam from patients suspected to suffer from TB were re-analyzed in Amsterdam by microscopy after
decontamination/concentration and using the new THM–GC–MS method. No false positives were found
by THM–GC–MS and all patients who were diagnosed with TB were also found positive using our newly
developed THM–GC–MS method. These results show that the newfast and sensitive THM–GC–MS method
holds great potential for the diagnosis of TB.
- Metabolic Profiling of Ultrasmall Sample Volumes
with GC/MS: From Microliter to Nanoliter Samples
Maud M. Koek, Floor Bakels, Willem Engel, Arn van den Maagdenberg, Michel D. Ferrari, Leon Coulier and Thomas Hankemeier. Anal. Chem., 2010, 82 (1), pp 156–16
<< Read Abstract >>
Profiling of metabolites is increasingly used to study
the functioning of biological systems. For some studies the volume of available samples is limited to only a few microliters
or even less, for fluids such as cerebrospinal fluid (CSF) of small animals like mice or the analysis of individual oocytes.
Here we present an analytical method using in-liner silylation coupled to gas chromatography/mass spectrometry (GC/MS),
that is suitable for metabolic profiling in ultrasmall sample volumes of 2 µL down to 10 nL. Method performance
was assessed in various biosamples. Derivatization efficiencies for sugars, organic acids, and
amino acids were satisfactory (105-120%), and repeatabilities were generally better than 15%, except for amino acids
that had repeatabilities up to about 35-40%. For endogenous sugars and organic acids in fetal bovine serum, the response
was linear for aliquots from 10 nL up to at least 1 µL. The developed GC/MS method was applied for the analysis of different s
ample matrixes, i.e., fetal bovine serum, mouse CSF, and aliquots of the intracellular content of Xenopus laevis oocytes.
To the best of our knowledge, we present here the first comprehensive GC/MS metabolite profiles from mouse CSF and from
the intracellular content of a single X. laevis oocyte.
- Comprehensive gas chromatography with Time of Flight MS and large volume
introduction for the detection of fluoride-induced regenerated nerve agent in
biological samples
J.A. van der Meer, H.C. Trap, D. Noort, M.J. van der Schans. in press: J. Chromatogr. B (2010), doi:10.1016/j.jchromb.2010.02.019
<< Read Abstract >>
Recently, several methods have been developed to verify exposure to nerve agents. Most of these
methods, such as the fluoride reactivation technique and the analysis of inhibited phosphonylated
butyrylcholinesterase (BuChE), are based on mass spectrometry. The high specificity of the mass spectrometer
might also imply a disadvantage, because the acquisition mass, i.e. the identity of the analyte
must be known beforehand in order to direct the MS analysis in the most sensitive mode. In real cases,
the identity of the nerve agent is not always known beforehand and the mass spectrometer should be
operated in a scanning mode, with the consequence that sensitivity of the method will be lower. Comprehensive
GC, or GC×GC, is a technique which offers enhanced separation. The implied larger selectivity
of the GC separation allows mass spectrometry to be conducted in a less specific, scanning, mode. By the
use of this configuration, the identity of the nerve agent does not have to be known beforehand but can be
traced. In order to be able to detect lower concentrations and assess lower exposure levels, a large volume
injection technique was developed allowing sample sizes up to 100µL. The technique was tested with
plasma samples that had been inhibited with various nerve agents. Subsequently, the cholinesterasebound
nerve agent was regenerated by the fluoride reactivation technique. Using the newly developed
comprehensive GC–MS method it was possible to detect nerve agent at an exposure level of 1% BuChE
inhibition, which is approximately 70 pg nerve agent/mL. These low exposure levels cannot be verified
with a cholinesterase (ChE) activity assay. Moreover, the identity of the regenerated nerve agent was
verified by the mass spectrum that was generated by the TOF mass spectrometer. This paper presents a
technique able to deliver full-scan data on the analysis of nerve agents in biomedical samples at relevant
exposure levels (1% BuChE inhibition). This full-scan data meets for a large part the forensic requirements
that are in place for the analysis of biomedical samples in the context of alleged use of Chemical Warfare
Agents.
- High Throughput Analysis of 150 Pesticides in Fruits and Vegetables using QuEChERS
and Low-Pressure Gas Chromatography–Time-of-Flight Mass Spectrometry
Urairat Koesukwiwat Steven J. Lehotay, Shui Miao and Natchanun Leepipatpiboon. in press: J. Chromatogr. A (2010.05.012)
<< Read Abstract >>
A higher monitoring rate is highly desirable in the labs, but this goal is typically limited by sample throughput. In this study,
we sought to assess the real-world applicability of fast, low-pressure GC - time-of-flight MS (LP-GC/TOFMS) for the identification and
quantification of 150 pesticides in tomato, strawberry, potato, orange, and lettuce samples. Buffered and unbuffered versions
of QuEChERS (which stands for “quick, easy, cheap, effective, rugged, and safe”) using dispersive solid-phase extraction
(d-SPE) and disposable pipette extraction (DPX) for cleanup were compared for sample preparation. For clean-up of all
sample types, a combination of 150 mg MgSO4, 50 mg primary secondary amine (PSA), 50 mg C18, and 7.5 mg graphitized
carbon black (GCB) per mL extract was used. No significant differences were observed in the results between the different
sample preparation versions. QuEChERS took <10 min per individual sample, or <1 hr for 2 chemists to prepare 32 pre-homogenized samples,
and using LP-GC/TOFMS, <10 min run time and <15 min cycle time allowed >32 injections in 8 hrs. Overall, >126 analytes gave
recoveries (3 spiking levels) in the range of 70-120% with <20% RSD. The results indicate that LP-GC/TOFMS for GC-amenable
analytes matches UHPLC-MS/MS in terms of sample throughput and turnaround time for their routine, concurrent use in the analysis of a
wide range of analytes in QuEChERS extracts to achieve reliable quantification and identification of pesticide residues in foods.
- Large-volume Injection Coupled to Comprehensive Gas Chromatography— Time-of-Flight Mass Spectrometry for the Analysis of 3-MCPD Esters in Edible Oils
By Sjaak de Koning, Zuzana Zelinkova, Karel Hrncirik, and Hans-Gerd Janssen
. March 19, 2010 Vol. 6, Number 5 issue of The Column, Pages 17-22
<< Read Abstract >>
- Mass Spectrometry–Based Metabolic Profiling Reveals Different Metabolite Patterns in Invasive Ovarian Carcinomas and
Ovarian Borderline Tumors
Carsten Denkert, Jan Budczies, Tobias Kind, Wilko Weichert, Peter Tablack, Jalid Sehouli,
Silvia Niesporek, Dominique Könsgen, Manfred Dietel, and Oliver Fiehn
. Cancer Res 2006; 66: (22)10795-804. November 15, 2006
<< Read Abstract >>
Metabolites are the end products of cellular regulatory processes, and their levels can be regarded as the ultimate
response of biological systems to genetic or environmental changes. We have used a metabolite profiling approach to test
the hypothesis that quantitative signatures of primary metabolites can be used to characterize molecular changes
in ovarian tumor tissues. Sixty-six invasive ovarian carcinomas and nine borderline tumors of the ovary were analyzed by
gas chromatography/time-of-flight mass spectrometry (GCTOFMS) using a novel contamination-free injector system.
After automated mass spectral deconvolution, 291 metabolites were detected, of which 114 (39.1%) were annotated as known
compounds. By t test statistics with P < 0.01, 51 metabolites were significantly different between borderline tumors and
carcinomas, with a false discovery rate of 7.8%, estimated with repeated permutation analysis. Principal component analysis
(PCA) revealed four principal components that were significantly different between both groups, with the highest
significance found for the second component (P = 0.00000009). PCA as well as additional supervised predictive
models allowed a separation of 88% of the borderline tumors from the carcinomas. Our study shows for the first time that
large-scale metabolic profiling using GC-TOF MS is suitable for analysis of fresh frozen human tumor samples, and that
there is a consistent and significant change in primary metabolism of ovarian tumors, which can be detected using
multivariate statistical approaches. We conclude that metabolomics is a promising high-throughput, automated approach
in addition to functional genomics and proteomics for analyses of molecular changes in malignant tumors.
- Evaluation of comprehensive on-line liquid chromatography thermally assisted hydrolysis
and methylation-gas chromatography-mass spectrometry for characterization of sulfonated lignins.
Brudin S, Kaal E, Janssen HG, Schoenmakers P.
J Sep Sci. 2010 Nov;33(22):3604-11.
<< Read Abstract >>
Sulfonated lignins, used as dispersants in agrochemical formulations, have been characterized by hyphenation of ion-pair RPLC
and thermally assisted hydrolysis and methylation-GC-MC (THM-GC-MS). The chemical structure of a series of selected lignins
was evaluated, both in terms of overall composition and in terms of composition as a function of molecular size.
Some sulfonated lignins give rise to unstable formulations. In the compositional analysis, these samples were found to yield
additional fragments. A newly developed comprehensive method made it possible to monitor the occurrence of these fragments
as a function of molecular size. In addition to differences in the molecular size between "good" and "bad" batches,
clear differences in chemical composition were established.
- Parasitoids select plants more heavily infested with their caterpillar hosts: a new approach to aid interpretation of plant headspace volatiles
Robbie D. Girling, Alex Stewart-Jones, Julie Dherbecourt, Joanna T. Staley, Denis J. Wright and Guy M. Poppy
Proc. R. Soc. B doi:10.1098/rspb.2010.2725
<< Read Abstract >>
Plants produce volatile organic compounds (VOCs) in response to herbivore attack, and these VOCs can be used by parasitoids of the herbivore as
host location cues. We investigated the behavioural responses of the parasitoid Cotesia vestalis to VOCs from a plant-herbivore complex
consisting of cabbage plants (Brassica oleracea) and the parasitoids host caterpillar, Plutella xylostella. A Y-tube olfactometer was
used to compare the parasitoids' responses to VOCs produced as a result of different levels of attack by the caterpillar and equivalent
levels of mechanical damage. Headspace VOC production by these plant treatments was examined using gas chromatography-mass spectrometry.
Cotesia vestalis were able to exploit quantitative and qualitative differences in volatile emissions, from the plant-herbivore complex,
produced as a result of different numbers of herbivores feeding. Cotesia vestalis showed a preference for plants with more herbivores
and herbivore damage, but did not distinguish between different levels of mechanical damage. Volatile profiles of plants with different
levels of herbivores/herbivore damage could also be separated by canonical discriminant analyses. Analyses revealed a number of compounds
whose emission increased significantly with herbivore load, and these VOCs may be particularly good indicators of herbivore number,
as the parasitoid processes cues from its external environment.
to magazine
- Inlet derivatization for the GC analysis of organic acid mixtures
T. P. Lynch and A. P. K. Grosser CAST, Chromatogr. Sep. Technol., 2000(13), 12-15
<< Read Abstract >>
The procedure employed an Optic 200 PTV injector installed on a Chrompack CP9001 gas chromatograph with FID detection.
The injector was fitted with a liner packed with Supelcoport. The reactants were injected into the liner under stopped flow
conditions at 45°C and the temperature was then increased at 16°C/s to 250°C (held for 2 min).
A pressure pulse was then used to transfer the reaction products into the column for analysis.
The procedure was performed using 850µl portions of process stream samples (for acetic acid production) containing succinic
acid and laevulinic acid in THF to which 350µl of the derivatizing reagent [bis(trimethylsilyl)trifluroacetamide] was added.
A 1 µl portion of the resulting mixture was injected into the PTV inlet for derivatization to the silyl ester to occur.
The calibration graphs for succinic acid and laevulinic acid were linear over the ranges: 50-100% and 0-10%, respectively, and regression
coefficients were 0.9993 and 0.9998, respectively.
- Determination of cholesterol and triglycerides in serum lipoproteins using flow
field-flow fractionation coupled to gas chromatography–mass spectrometry
Rashid Nazir Qureshi, Erwin Kaal, Hans-Gerd Janssen, Peter J. Schoenmakers, Wim Th. Kok
Analytica Chimica Acta 2011.04.057
<< Read Abstract >>
Asymmetric flow field flow fractionation (AsFlFFF) was combined with pyrolysis-gas chromatography mass spectrometry for a sized based fractionation
and a detailed compositional study of the triglycerides and cholesterol associated with the various lipoprotein subclasses present in human serum.
Serum samples were injected in the AsFlFFF instrument and fractionated with a time-delayed exponential decay cross flow program.
The fractions collected after AsFlFFF elution were injected into a programmable temperature vaporizer (PTV) GC-injector, containing a fritted liner.
A temperature and split-flow program for the PTV injector was optimized for the thermally assisted hydrolysis and methylation of the compounds of interest.
The resulting fatty acid and cholesterol methyl esters were separated by GC and characteristic fragment ions were detected by MS.
The system was optimized and calibrated with triglyceride and cholesterol standards for quantitative analysis.
The possible interference by phospholipids with the quantitative results was investigated and found to be of minor importance.
The concentrations and lipoprotein profiles of triglycerides and cholesterol were determined in a pooled serum sample of healthy
volunteers and a serum sample of a sepsis patient. The results obtained with the GC–MS approach were compared with those of a previously
developed method based on AsFlFFF with a dual enzymatic reaction detection system.
A good agreement of the profiles was found, for cholesterol as well as for the triglycerides, even when the GC–MS method quantifies the fatty
acids while with the enzymatic reaction method the glycerol concentrations are determined. Total cholesterol and triglyceride concentration
values for the serum samples showed good agreement with the results of the standard enzymatic method as used in practice in the university hospital.
Graphical abstract
Highlights
> Lipoproteins from human serum were separated by size (HDL, LDL, VLDL) using field flow fractionation.
> Pyrolysis-GC–MS could be used to quantify cholesterol and triglycerides in the lipoprotein fractions.
> Cholesterol and triglyceride profiles measured in different samples were very similar to results obtained with other methods.
> Possibilities for fatty acid speciation and study of the cholesterol metabolism were shown.
Keywords: Lipoproteins; Cholesterol; Triglycerides; Asymmetric field flow fractionation; Pyrolysis-gas chromatography–mass spectrometry; Fatty acid profilin
- Pyrolysis–gas chromatography–mass spectrometry for studying N-vinyl-2-pyrrolidone-co-vinyl acetate copolymers and their dissolution behaviour
Aleksandra Chojnacka, Abdul Ghaffar, Andrew Feilden, Kevin Treacher, Hans-Gerd Janssen, Peter Schoenmakers
Analytica Chimica Acta IN PRESS
<< Read Abstract >>
Knowledge on the solubility behaviour and dissolution rate of speciality and commodity polymers is very important for the use of such materials in high-tech applications. We have developed methods for the quantification and characterization of dissolved copolymers of N-vinyl-2-pyrrolidone (VP) and vinyl acetate (VA) during dissolution in water. The methods are based on pyrolysis (Py) performed in a programmed-temperature vaporization injector with subsequent identification and quantification of the components in the pyrolysate using capillary gas chromatography–mass spectrometry (GC–MS). By injecting large volumes and applying cryo-focussing at the top of the column, low detection limits could be achieved.
The monomer ratio was found to have the greatest effect on the dissolution rate of the PVP-co-VA copolymers. The material with the highest amount of VA (50%) dissolves significantly slower than the other grades. Size-exclusion chromatography (SEC) and Py–GC–MS were used to measure molecular weights and average chemical compositions, respectively. Combined off-line SEC//Py–GC–MS was used to determine the copolymer composition (VP/VA ratio), as a function of the molecular weight for the pure polymers. In the dissolution experiments, a constant VP/VA ratio across the dissolution curve was observed for all copolymers analysed. This suggests a random distribution of the two monomers over the molecules.
Keywords: Copolymer dissolution; Copolymer characterization; Pyrolysis–GC–MS; SEC; N-vinyl-2-pyrrolidone; Vinyl acetate
- An automated method for the analysis of phenolic acids in plasma based on ion-pairing micro-extraction coupled on-line to gas chromatography/mass spectrometry with in-liner derivatisation
Sonja Peters, Erwin Kaal, Iwan Horsting, Hans-Gerd Janssen
doi:10.1016/j.chroma.2011.10.055
<< Read Abstract >>
A new method is presented for the analysis of phenolic acids in plasma based on ion-pairing ‘Micro-extraction in packed sorbent’ (MEPS) coupled on-line to in-liner derivatisation-gas chromatography-mass spectrometry (GC-MS). The ion-pairing reagent served a dual purpose. It was used both to improve extraction yields of the more polar analytes and as the methyl donor in the automated in-liner derivatisation method. In this way, a fully-automated procedure for the extraction, derivatisation and injection of a wide range of phenolic acids in plasma samples has been obtained.
An extensive optimisation of the extraction and derivatisation procedure has been performed. The entire method showed excellent repeatabilities of under 10% and linearities of 0.99 or better for all phenolic acids. The limits of detection of the optimised method for the majority of phenolic acids were 10 ng/mL or lower with three phenolic acids having less-favourable detection limits of around 100 ng/mL. Finally, the newly-developed method has been applied in a human intervention trial in which the bioavailability of polyphenols from wine and tea was studied. Forty plasma samples could be analysed within 24 h in a fully-automated method including sample extraction, derivatisation and gas chromatographic analysis.
Keywords: automation; gas chromatography; micro-extraction in a packed sorbent (MEPS); ion-pairing extraction; in-liner derivatisation; plasma; phenolic acids
- Methyl salicylate production in tomato affects biotic interactions
Kai Ament, Vladimir Krasikov, Silke Allmann, Martijn Rep, Frank L.W. Takken and Robert C. Schuurink
The Plant Journal (2010) 62, 124–134
<< Read Abstract >>
The role of methyl salicylate (MeSA) production was studied in indirect and direct defence responses of tomato
(Solanum lycopersicum) to the spider mite Tetranychus urticae and the root-invading fungus Fusarium
oxysporum f. sp. lycopersici, respectively. To this end, we silenced the tomato gene encoding salicylic acid
methyl transferase (SAMT). Silencing of SAMT led to a major reduction in SAMT expression and MeSA
emission upon herbivory by spider mites, without affecting the induced emission of other volatiles
(terpenoids). The predatory mite Phytoseiulus persimilis, which preys on T. urticae, could not discriminate
between infested and non-infested SAMT-silenced lines, as it could for wild-type tomato plants. Moreover,
when given the choice between infested SAMT-silenced and infested wild-type plants, they preferred the
latter. These findings are supportive of a major role for MeSA in this indirect defence response of tomato.
SAMT-silenced tomato plants were less susceptible to a virulent strain of F. oxysporum f. sp. lycopersici,
indicating that the direct defense responses in the roots are also affected in these plants. Our studies show that
the conversion of SA to MeSA can affect both direct and indirect plant defence responses.
Keywords: methyl salicylate, Fusarium, tomato, spider mite, predatory mite.
- Quality Evaluation of Olive Oil by Statistical Analysis of
Multicomponent Stable Isotope Dilution Assay Data of Aroma Active Compounds
Georg Dierkes, Annette Bongartz, Helmut Guth and Heiko Hayen.
dx.doi.org/10.1021/jf203406s | J. Agric.Food Chem.
<< Read Abstract >>
An instrumental method for the evaluation of olive oil quality was developed. Twenty-one relevant aroma active
compounds were quantified in 95 olive oil samples of different quality by headspace solid phase microextraction (HS-SPME) and
dynamic headspace coupled to GC-MS. On the basis of these stable isotope dilution assay results, statistical evaluation by partial
least-squares discriminant analysis (PLS-DA) was performed. Important variables were the odor activity values of ethyl
isobutanoate, ethyl 2-methylbutanoate, 3-methylbutanol, butyric acid, E,E-2,4-decadienal, hexanoic acid, guaiacol, 2-phenylethanol,
and the sum of the odor activity values of Z-3-hexenal, E-2-hexenal, Z-3-hexenyl acetate, and Z-3-hexenol. Classification performed
with these variables predicted 88% of the olive oils’ quality correctly. Additionally, the aroma compounds, which are characteristic for
some off-flavors, were dissolved in refined plant oil. Sensory evaluation of these models demonstrated that the off-flavors rancid, fusty,
and vinegary could be successfully simulated by a limited number of odorants.
Keywords:methyl salicylate, Fusarium, tomato, spider mite, predatory mite.
- Rapid Multidimensional Liquid–Gas Chromatography for the Analysis of Saturated Hydrocarbon Contamination in Foods containing Vegetable Oil
Paola Dugo, Luigi Mondello, Peter Q. Tranchida, Mariosimone Zoccali
Jan 1, 2012 | LCGC Europe
<< Read Abstract >>
This article describes a rapid heart-cutting liquid chromatography–gas chromatography (LC–GC) method for the analysis of mineral oil saturated hydrocarbons (MOSHs) found in a range of widely-consumed foods, including crisps, margarine, tinned tuna and vegetable oils.
The automated LC–GC experiments were performed using a system equipped with a syringe-type interface capable of both heart-cutting and comprehensive two-dimensional analysis. The first dimension separation was achieved on a silica column operated under isocratic conditions using hexane. The heart-cuts were then transferred to a programmed temperature vaporizer. After the large volume injection (LVI), the target analytes were rapidly separated (~ 9 min) using a micro-bore GC capillary column. The overall LC–GC run time enabled the analysis of around four samples in an hour. Various degrees of MOSH contamination — ranging from "not detected" to around 390 mg/kg — were discovered in the thirty samples that were subjected to analysis.
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