Environmental applications of large volume injection in capillary GC using PTV injectors

Mutual interference between 3,6-dichlorinated carbazole and p,p'-dichlorodiphenyltrichloroethane in gas chromatography mass spectrometry analysis

The widespread contamination of the environment by polyhalogenated carbazoles (PHCZs) has been increasingly observed during the past decade. Among numerous PHCZ congeners, 3,6-dichlorocarbazole (36-CCZ) is often among the most frequently detected at higher concentrations. Although the environmental level of the legacy pesticide p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT) has been declining, it continues to be ubiquitously detected. These two compounds were found to interfere with each other during analyses using gas chromatography (GC) coupled with single- or triple-quadrupole low-resolution mass spectrometry (MS or MS/MS). The base peak in the mass spectra was that of m/z 235 for both compounds. In MS/MS with multiple reaction monitoring (MRM), the same transitions (235 → 200 and 235 → 165) were often used. Under the same GC operating conditions, the SH-I-5MS capillary column used in this work did not resolve the two compounds at baseline. Pre-treatment using cleanup column chromatography can fractionate the sample extract, with the two compounds separated in different fractions before instrumental analyses. Reversed-phase HPLC columns also work for resolving 36-CCZ and p,p'-DDT. Possible overlaps in GC retention and similarity in MS spectra might have caused data inaccuracy for 36-CCZ as well as p,p'-DDT in some studies published to date, and steps to avoid the interference should be taken into quality control protocols in future research and environmental monitoring.

Optimization of a large-volume injection method for compound-specific isotope analysis of polycyclic aromatic compounds at trace concentrations

RATIONALE

Compound-specific isotope analysis (CSIA) of persistent organic contaminants can be used for source apportioning in the environment if appropriate sensitivity can be achieved. This paper describes the optimization and validation of a sensitive analytical approach for the determination of the carbon isotope composition of semi-volatile organic compounds, such as polycyclic aromatic hydrocarbons (PAHs).

METHODS

Analyses are based on the introduction of up to 150 μL of organic extracts by means of programmed temperature vaporization-large-volume injection combined with gas chromatography coupled to isotope ratio mass spectrometry (PTV-LVI-GC/IRMS). To allow for the analysis of more volatile, low-molecular-weight PAHs, the PTV injector was equipped with a sub-ambient/cryogenic cooling. Accuracy, precision, linearity and determination limits for application in isotope analysis were evaluated for a set of individual PAHs ranging from two- to five-ring molecular structures. The method was exemplified by determining the δ(13) C values of individual PAHs in soil samples in a source apportionment study at a contaminated site.

RESULTS

The choice of PTV injection parameters is crucial to prevent isotope fractionation during injection and largely depends on the analytes to be determined. The observed isotope fractionation effect on semi-volatiles depends on the applied solvent and injection temperature and demonstrates the importance of performing appropriate tests with given PTV parameters for each of the compounds of interest. The proposed PTV-LVI-GC/IRMS method allows the carbon isotope ratio (δ(13) C value) of individual PAHs to be determined accurately and precisely at concentrations of 0.04-0.1 ng μL(-1) even for volatile PAHs such as naphthalene or acenaphthene.

CONCLUSIONS

LVI with PTV injector cooling allows for the isotopic analysis of volatile and semi-volatile PAHs at trace concentrations, thus considerably expanding the applicability of CSIA in environmental studies.

Large-volume injection combined with gas chromatography/isotope ratio mass spectrometry for the analysis of polycyclic aromatic hydrocarbons

RATIONALE

Compound-specific stable isotope analyses of carbon require relatively large amounts of sample for reliable analyses. Commonly applied injections of 1 μL may thus be insufficient for samples with low concentrations of pollutants (e.g. air particulate matter) or when the amount of a sample is limited.

METHODS

A Large-Volume Injection (LVI) method for carbon stable isotope ratio analysis of Polycyclic Aromatic Hydrocarbons (PAHs) was optimized in this study. Gas chromatography/combustion/isotope ratio mass spectrometry (GCCIRMS) and ion trap mass spectrometry (ITMS) were used for the determination of stable carbon isotope ratios and quantification of compounds, respectively.

RESULTS

The optimized method resulted in very good reproducibility, even for the most volatile PAH, naphthalene, when a small amount of higher boiling co-solvent was used. No significant fractionation of isotope ratios could be seen and the recoveries of analytes were similar to or better than that of a splitless cold injection.

CONCLUSIONS

Injection of 100 μL, instead of the commonly used 1 μL, increases the detection limit for PAHs significantly and/or simplifies the sample preparation step. Using our optimized method, stable carbon isotope ratios can be reliably measured in samples with concentrations of PAHs down to 0.05-0.1 ng μL(-1).

Critical evaluation of the determination of pharmaceuticals, personal care products, phenolic endocrine disrupters and faecal steroids by GC/MS and PTV-GC/MS in environmental waters

An analytical method is described for the determination of a broad range of emerging and priority pollutants, together with sewage molecular markers in environmental waters. The step-by-step study of the GC/MS analyses focuses on the effects of experimental variables using a large volume injection (LVI) technique [a programmed temperature-vaporising (PTV) inlet], the evaluation of a clean-up step using classical and newer sorbents (i.e. Al-N, Fl, NH(2), PSA, Si, CN and DIOL), and the revision of how organic matter [i.e. humic acids (HA) content] affects method performance. Reproducibility and recoveries from spiked coastal water samples at different analyte concentrations (100, 250 and 500 ng L(-1)) as well as with different levels of spiked humic acids (2, 10 and 20 mg L(-1)) are reported indicating a good performance of the extraction procedure with low levels of HA (<10 mg L(-1)). The presence of HA is a critical parameter during the solid-phase extraction (SPE) procedures. Of the clean-up sorbents tested, CN and DIOL proved most efficient in cleaning-up the extracts with recoveries in the range of 66-77% and 100-114%, respectively for the selected analytes. Both GC/MS and PTV-GC/MS instrumental configurations were tested using final sewage effluents, riverine, estuarine and coastal water samples. However, limited applicability of the PTV inlet is reported for environmental applications, affording only a modest improvement in chromatographic signal-to-noise ratios.

Use of a temperature-programmable injector coupled to gas chromatography-combustion-isotope ratio mass spectrometry for compound-specific carbon isotopic analysis of polycyclic aromatic hydrocarbons

Compound-specific isotopic analysis (CSIA) can provide information about the origin of analysed compounds; for instance, polycyclic aromatic hydrocarbons (PAHs) in aerosols. This could be a valuable tool in source apportionment of particulate matter (PM) air pollution. Because gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) analysis requires an amount of at least 10 ng of an individual PAH, a high concentration of PAHs in the injected extract is needed. When the concentration is low a large volume injector creates the possibility of introducing a satisfactory amount of individual PAHs. In this study a temperature-programmable injector was coupled to GC-C-IRMS and injection parameters (solvent level, transfer column flow, transfers time) were optimised using six solid aromatic compounds (anthracene, fluoranthene, pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene) dissolved in n-pentane and EPA 610 reference mixture. CSIA results for solid PAHs were compared with results obtained for the single components analysed by elemental analysis-isotope ratio mass spectrometry. The injection method was validated for two sample injection volumes, 50 and 100 microL. This method was also compared with commonly used splitless injection. To be included in the study, measurements had to have an uncertainty lower than 0.5 per thousand for delta(VPDB)13C and a minimum peak height of 200 mV. The lower concentration limits at which these criteria were fulfilled for PAHs were 30 mg/L for 1 microL in splitless injection and 0.3 and 0.2 mg/L for 50 and 100 microL, respectively, in large volume injection.

High-throughput quantitative metabolomics: workflow for cultivation, quenching, and analysis of yeast in a multiwell format

Metabolomics is a founding pillar of quantitative biology and a valuable tool for studying metabolism and its regulation. Here we present a workflow for metabolomics in microplate format which affords high-throughput and yet quantitative monitoring of primary metabolism in microorganisms and in particular yeast. First, the most critical step of rapid sampling was adapted to a multiplex format by using fritted 96-well plates for cultivation, which ensure fast sample transfer and permit us to use well-established quenching in cold solvents. Second, extensive optimization of large-volume injection on a GC/TOF instrument provided the sensitivity necessary for robust quantification of 30 primary metabolites in 0.6 mg of yeast biomass. The metabolome profiles of baker's yeast cultivated in fritted well plates or in shake flasks were equivalent. Standard deviations of measured metabolites were between 10% and 50% within one plate. As a proof of principle we compared the metabolome of wild-type Saccharomyces cerevisiae and the single-deletion mutant Delta sdh1, which were clearly distinguishable by a 10-fold increase of the intracellular succinate concentration in the mutant. The described workflow allows the production of large amounts of metabolome samples within a day, is compatible with virtually all liquid extraction protocols, and paves the road to quantitative screens.

Analysis of polycyclic aromatic hydrocarbons (PAHs) in environmental samples: a critical review of gas chromatographic (GC) methods

Polycyclic aromatic hydrocarbons (PAHs) are frequently measured in the atmosphere for air quality assessment, in biological tissues for health-effects monitoring, in sediments and mollusks for environmental monitoring, and in foodstuffs for safety reasons. In contemporary analysis of these complex matrices, gas chromatography (GC), rather than liquid chromatography (LC), is often the preferred approach for separation, identification, and quantification of PAHs, largely because GC generally affords greater selectivity, resolution, and sensitivity than LC. This article reviews modern-day GC and state-of-the-art GC techniques used for the determination of PAHs in environmental samples. Standard test methods are discussed. GC separations of PAHs on a variety of capillary columns are examined, and the properties and uses of selected mass spectrometric (MS) techniques are presented. PAH literature on GC with MS techniques, including chemical ionization, ion-trap MS, time-of-flight MS (TOF-MS), and isotope-ratio mass spectrometry (IRMS), is reviewed. Enhancements to GC, for example large-volume injection, thermal desorption, fast GC, and coupling of GC to LC, are also discussed with regard to the determination of PAHs in an effort to demonstrate the vigor and robustness GC continues to achieve in the analytical sciences.

Evaluation of a dedicated gas chromatography–mass spectrometry method for the analysis of phenols in water

The increasing need to routinely analyse phenolic hydrocarbons in aqueous samples was addressed by the development and implementation of a state-of-the-art, though relatively straightforward, analytical procedure. The proposed method is based on acetic anhydride derivatisation of the native phenols, liquid-liquid extraction of the corresponding phenyl acetate esters and subsequent analysis by GC-MS. The key feature and main strength of the method is located at the injection step which applies 'at-once' large volume injection with a programmable temperature vaporizer (PTV)-type injector. In the proposed method, the sensitivity gain inherent to the higher injection volume was used entirely to proportionally miniaturize, considerably accelerate and effectively simplify the otherwise tedious and time-consuming derivatisation/extraction step. Method performance, as expressed in terms of repeatability, reproducibility, linearity and accuracy, was found to be excellent. R.S.D. values, determined in the framework of an extensive reproducibility study, ranged between 1.47 and 9.02%. Detection limits were in the low ng/L range for all compounds with linear ranges extending up to two orders of magnitude. Method accuracy was determined by analyzing a certified reference material (PH- 1JM), spiked water samples and participating in a series of round robin tests and did not reveal any significant bias for the different compounds under investigation.

Miniaturised pressurised liquid extraction of chloroanilines from soil with subsequent analysis by large-volume injection–gas chromatography–mass spectrometry

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.

Comprehensive two-dimensional gas chromatography using large sample volume injection for the determination of polynuclear aromatic hydrocarbons in complex matrices

The sensitivity of a gas chromatography (GC) analytical method can be substantially enhanced by injecting large sample volumes. The novel Large Volume Splitless injection technique was used in combination with comprehensive two-dimensional GC (GC x GC), taking advantage of the improved detectability and the very high separation capability. An experimental version of Thermo Electron TRACE GC Ultra using a cryogenic dual jet modulator was utilized with a fast flame ionization detector (FID) for the analysis of low ppbs level of PAHs compounds in very complex matrices. Experimental data (relative standard deviation of 1% evaluated on a standard mixture) demonstrate the reliability of the whole system. A dedicated data system is presented for acquiring and managing GC x GC data: three-dimensional and color plot visualization, peaks integration, identification and quantitation are functions available with the software.

Determination of polar organophosphorus pesticides in vegetables and fruits using liquid chromatography with tandem mass spectrometry: selection of extraction solvent

A method based on liquid chromatography (LC)-mass spectrometry (MS)/MS was developed for sensitive determination of a number of less gas chromatography (GC)-amenable organophosphorus pesticides (OPs; acephate, methamidophos, monocrotophos, omethoate, oxydemeton-methyl and vamidothion) in cabbage and grapes. For extraction, several solvents were evaluated with respect to the possibility of direct injection, matrix-induced suppression or enhancement of response, and extraction efficiency. Overall, ethyl acetate was the most favourable solvent for extraction, although a solvent switch was required. For some pesticide/matrix combinations, reconstitution of the residue after evaporation required special attention. Extracts were analysed on a C18 column with polar endcapping. The pesticides were ionised using atmospheric pressure chemical ionisation on a tandem mass spectrometer in multiple reaction monitoring mode. The final method is straightforward and involves extraction with ethyl acetate and a solvent switch to 0.1% acetic acid/water without further cleanup. The method was validated at the 0.01 and 0.5 mg/kg level, for both cabbage and grapes. Recoveries were between 80 and 101% with R.S.D. < 11% (n = 5). The limit of quantification was 0.01 mg/kg and limits of detection were between 0.001 and 0.004 mg/kg.

On-line coupled liquid chromatography-gas chromatography

On-line coupled liquid chromatography-gas chromatography (LC-GC) is a powerful technique that combines the best features of LC and GC and is ideal for the analysis of complex samples. This review describes the unique features of on-line coupled LC-GC. The different interfaces and evaporation techniques are presented, along with their advantages and disadvantages. Guidelines are given for selecting a suitable LC-GC technique and representative applications are noted.

Large-volume programmed-temperature vaporiser injection for fast gas chromatography with electron capture and mass spectrometric detection of polybrominated diphenyl ethers

A large volume injection fast-GC-MS method has been developed, optimized and evaluated for the determination of polybrominated diphenyl ethers, including the decabrominated diphenyl ether (BDE-209). The programmed-temperature vaporiser injection parameters, temperature programming of the GC oven, and the physical dimensions of the narrow bore GC column were investigated to find the optimal operating conditions for the analysis. Depending on parameter settings the yield of the PBDEs and particularly BDE-209, varies significantly. Volumes up to 125 microl were successfully injected and a fast GC separation was performed, with retention times as short as 6.4 min for the last eluting compound, BDE-209. In a pilot study an air sample, collected at an electronics dismantling facility, was analyzed. Low-resolution mass spectrometry in electron capture negative ion mode was used for detection. Nine BDE congeners, including BDE-209, were identified and quantified.

A comparative study of the correction of systematic errors in the quantitation of pyrethroids in vegetables using calibration curves prepared using standards in pure solvent

A comparative study of two mathematical approaches was performed in order to correct systematic errors due to the presence of the unexpected interferences which appear when the quantitation of the analyte in real samples is carried out with calibration curves built using standards in pure solvent. These methods consisted in the establishment of different mathematical expressions which transform the concentration (Cs) obtained using calibration graphs built using pure solvent into the corrected concentration (C(M)) that should be obtained if the quantitation is carried out with calibration curves built using standards dissolved in blank matrix extracts. In the two approaches the correction is performed from the results of an intermediate precision study which was carried out using both calibration graphs (prepared using pure solvent and blank matrix extract). By using ANCOVA to compare the slope of both solvent-based and matrix-matched calibration graphs, matrix effect was found in the determination of deltamethrin in tomato and acrinathrin in tomato and pepper. In these cases, both approaches led to good results.

Optimisation of a programmed split-splitless injector in the gas chromatographic-mass spectrometric determination of organochlorine pesticides

Large-volume injection techniques in gas chromatography are used to compensate for the at times limited detection sensitivity of mass spectrometric detection. In this work a programmed split-splitless injector in solvent split mode was employed to determine organochlorine pesticides in environmental samples. The injection conditions were selected by a Plackett-Burman design followed by a central composite design. The LODs obtained in the optimum conditions were compared with those obtained with splitless-MS and splitless-ECD. Finally, the method was applied to a soil sample.

Determination of cannabinoids by gas chromatography-mass spectrometry and large-volume programmed-temperature vaporiser injection using 25 microl of biological fluid

This paper presents a GC-MS confirmation method, based on large-volume programmed-temperature vaporisation (PTV) injection, for the determination of cannabinoids in plasma samples (or whole blood) with deuterium-labelled internal standards using only 25 microl of biological fluid. The analytes, Delta(9)-tetrahydrocannabinol (THC), 11-hydroxy-Delta(9)-tetrahydrocannabinol (11-OH-THC) and 11-nor-9-carboxy-Delta 9-tetrahydrocannabinol (THC-COOH), were enriched by means of solid-phase extraction cartridges containing octadecyl-bonded silica and were, subsequently, methylated. A 20 microl aliquot of an extract in hexane was injected into a PTV in solvent split mode. Method development and the results of the analyses of standard reference material and real samples are presented and discussed. This micro-method is precise and sensitive enough to assess relevant cannabinoid levels in human blood for forensic investigations as well as for clinical applications.

Performance of programmed temperature vaporizer, pulsed splitless and on-column injection techniques in analysis of pesticide residues in plant matrices

A programmed temperature vaporizer (PTV) injection technique has been recently implemented in our laboratory. In present paper its performance is compared with other GC injection techniques commonly used in trace analysis of organic contaminants. Twenty-six pesticides representing different chemical classes were selected for the study. This group comprised compounds typically subjected to discrimination in the injection port of the gas chromatograph, e.g., polar organophosphorus pesticides and thermolabile carbamates. In the first set of experiments standards in pure solvent were injected into GC systems employing different types of injection, i.e., (i) on-column, (ii) pulsed splitless, (iii) PTV solvent split, (iv) PTV splitless, and the responses of analytes were compared. Discrimination of troublesome compounds was significantly decreased with the application of PTV solvent split injection. In the second set of experiments repetitive injections of purified wheat samples were performed, with aims to evaluate the long-term stability of responses, as well as matrix effects in different stages of system contamination for each injection technique. The tolerance of the GC system to co-injected matrix components was increased in the order: on-column<pulsed splitless<PTV solvent split technique. As regards matrix effects, these were suppressed considerably with the PTV solvent split technique in comparison with pulsed splitless injection. With the latter technique after 66 injections of wheat samples relative responses (apparent recovery) reached as much as 450% for some compounds, while with the application of PTV matrix effects did not exceed 200% under the same conditions.

Determination of polar organophosphorus pesticides in aqueous samples by direct injection using liquid chromatography-tandem mass spectrometry

It was demonstrated that four out of six of the very polar organophosphorus pesticides (OPs), i.e. acephate, methamidophos, monocrotophos, omethoate, oxydemeton-methyl and vamidothion, could not be extracted from water using commonly available SPE cartridges. In addition, GC analysis on all six compounds was found to be troublesome due to their polar and thermolabile character. This initiated the development of an alternative highly sensitive and selective method for the determination of the above mentioned very polar OPs in water, based on LC-MS. Large volume (1 ml) water samples were directly injected onto an RP18 HPLC column with a polar endcapping. The latter was essential for obtaining retention and maintaining column performance under 100% aqueous conditions during the sampling. The compounds were ionized using atmospheric pressure chemical ionization and detected on a tandem mass spectrometer operated in multiple reaction-monitoring mode. The detection limits were in the range of 0.01-0.03 microg/l. Compared to conventional GC methods, the developed LC-MS procedure is very straightforward, fast and more reliable. This application demonstrates the applicability of LC-MS for analysis of polar OPs in surface, ground and drinking water, as a more favourable alternative to GC.

On-line membrane extraction liquid chromatography for monitoring semi-volatile organics in aqueous matrices

Membrane extraction is an attractive alternative to conventional extraction methods, such as liquid-liquid extraction and solid phase extraction, because the analytes can be isolated in a continuous fashion. On-line detection can be carried out using a suitable analytical instrument. The objective of this study is to study the enrichment of semi-volatile organic compounds (SVOCs) from an aqueous matrix by on-line membrane extraction, to be followed by liquid chromatographic (ME-LC) analysis for continuous monitoring. The membrane serves as an interface across which liquid-liquid extraction takes place. The SVOCs transfer from the aqueous phase and are concentrated in an organic extractant. The enriched solvent is intermittently injected into an HPLC for analysis. In this paper, the enrichment into the organic phase under different operating conditions and the performance characteristics of the instrumentation are presented.

Miniaturised pressurised liquid extraction of polycyclic aromatic hydrocarbons from soil and sediment with subsequent large-volume injection-gas chromatography

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 microl 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.

Determination of endocrine disruptors in water after derivatization with N-methyl-N-(tert.-butyldimethyltrifluoroacetamide) using gas chromatography with mass spectrometric detection

The combined gas chromatographic determination of a number of hydroxyl-group containing endocrine disruptors, including 4-octylphenol, 4-nonylphenol, 2,4-dichlorophenol, pentachlorophenol, 4-tert.-butylbenzoic acid, bisphenol-A, 17beta-estradiol and 17alpha-ethynylestradiol, was investigated. Derivatization, required for sensitive determination of these compounds, was carried out using N-methyl-N-(tert.-butyldimethyltrifluoroacetamide). A number of parameters affecting the derivatization reaction, like temperature, time, matrix, solvent, and amount of reagent were studied in detail. Quantitative yields were obtained for real-life extracts after optimization, but the hormones were only mono-substituted. Both solid-phase extraction (SPE) and liquid-liquid extraction were studied as extraction methods, with emphasis on SPE material and effect of pH. Recoveries and RSD for analysis of surface water samples were 58-106 and 6-16% (n=4), respectively, when using SPE, and 109-117 and 6-14% (n=6) when using liquid-liquid extraction. The method developed allows routine analysis of surface water for traces of endocrine disruptors. The limits of detection of were 4-6 ng/l but higher for the hormones.

Gas chromatography with spectroscopic detectors

In recent years, capillary gas chromatography (GC) with Fourier Transform Infrared (FT-IR) and/or mass spectral (MS) detection has become a primary analytical tool for qualitative and quantitative analysis of complex mixtures. Because of the wide range of applications, the analytical requirements have motivated a variety of chromatographic and detection developments. This review examines those, illustrating with applications that demonstrate the power of GC and multidimensional GC-MS, GC-FT-IR and GC-FT-IR-MS systems for solving a variety of analytical problems. In addition, the article discusses the integrated performance of such analytical systems with the aid of recent sample introduction and computer data analysis advances.

Programmed temperature vaporiser-based injection in capillary gas chromatography

The application of programmed temperature vaporisation (PTV) in capillary gas chromatographic analysis is reviewed. The development of the different strategies as well as the state of the art are described. As the analytes are normally enriched in the PTV insert, the quoted papers are subdivided depending on whether the enrichment was carried out from organic solvents, from water or from gaseous media. Furthermore, the possibilities of PTVs for on-line coupling with sample preparation methods or other separation techniques and their use as thermoreactors are mentioned.

Trace analysis of pesticides by gas chromatography

The analysis of pesticides is relevant to both food quality and the environment. Many laboratories are occupied with the analysis of pesticides in food, water or soil. Capillary gas chromatography is the technique most widely used in pesticide analysis. In present laboratory practice it serves as a screening method for over 300 pesticides. In this review we describe the role of gas chromatography as an analytical tool in combination with currently used or recently developed sample preparation techniques.