全二维气相色谱分析持久性有机污染物的应用进展

持久性有机污染物（POPs）组分复杂,在自然界中超痕量存在,其分离分析十分困难。全二维气相色谱（GC×GC）作为一种新型色谱技术,与传统的一维气相色谱相比,具有峰容量大、分辨率和灵敏度高等优势,越来越广泛地应用于环境有机污染物的分析。该文综述了近十年来全二维气相色谱在持久性有机污染物分析中的应用进展,主要包括全二维气相色谱在解决一些复杂POPs定性定量分析难题方面的应用,如二恶英、毒杀芬和短链氯化石蜡等;概述了全二维气相色谱对多种POPs同时定性定量分析的应用进展;讨论了全二维气相色谱在非目标有机污染物筛查分析中的应用,并对发展趋势及相关应用前景进行了总结展望。     

Comprehensive two-dimensional gas chromatography for fast screening of wash oils

Fast screening of wash oils is demonstrated using comprehensive two-dimensional gas chromatography (GCxGC). Wash oils are used in ethylene production plants to minimize compressor fouling. The composition of a wash oil determines its effectiveness in solubilizing heavy hydrocarbons. In particular, the relative amount of 1- and 2-ring aromatics is important. The presence of oxygenates is undesirable because of adverse effects to the process. It is shown that GCxGC is well suited for this application. Species in wash oils are separated and grouped into three bands: a nonpolar aliphatics band, 1- and 2-ring aromatics band, and polyaromatics band. For a given polar secondary column, the spacing between bands in the second dimension can be adjusted in a broad range by selecting a primary column and an oven-temperature-programming rate. Integration of GCxGC peaks is evaluated using a standard GC integration program and a new GCxGC integration program. Consistent results are obtained using both programs for well-separated GCxGC peaks with relative differences for individual peak ranging from 0.04% to 1.6%. Peak responses are integrated by the GCxGC software, and the relative amounts of aromatics content and aliphatics content are estimated by peak response percent with relative standard deviations ranging from 0.15% to 2.8% (n = 3).     

Group separation of organohalogenated compounds by means of comprehensive two-dimensional gas chromatography

Separations of 12 compound classes, polychlorinated biphenyls (PCBs), diphenyl ethers (PCDEs), naphthalenes (PCNs), dibenzothiophenes (PCDTs), dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), terphenyls (PCTs) and alkanes (PCAs), toxaphene, organohalogenated pesticides (OCPs), and polybrominated biphenyls (PBBs) and diphenyl ethers (PBDEs) by comprehensive two-dimensional gas chromatography were evaluated. Five column combinations, DB-1 x 007-210, DB-1 x HT-8, DB-1 x LC-50, DB-1 x 007-65HT and DB-1 x VF-23ms were used to study, primarily, group-type separations, but attention was devoted also to within-class separation, especially for those classes which were not addressed in much detail before, the PCNs, OCPs, PBBs and PCTs. The DB-1 x 007-210 column set did not offer any extra separation compared to one-dimensional GC. For the DB-1 x HT-8 column combination, the useful principle of congener separation on the basis of number of halogen substituents in a molecule was confirmed (PCBs, toxaphene) and extended (PCTs, PBDEs). No practically useful group-type separation was observed for this column combination. The DB-1 x LC-50 set provides group separation based on planarity: planar compounds such as PCDDs, PCDFs, PCDTs and PCNs are much more retained than, and therefore separated from, non-planar analytes. Within the classes of PCBs, PBBs and PCTs highly useful separation of planar from non-planar compounds was also observed. The DB-1 x 007-65HT column set effectively separates PCAs and PBDEs from all other compound classes, and provides a good separation of brominated and chlorinated analogue classes from each other. This column set was the most efficient one for within-class separation of OCPs and PCNs. Finally, DB-1 x VF-23ms yields excellent within-class separations, especially of non-aromatic compounds, viz. OCPs, toxaphene and PCAs. No group separation was observed here. The applicability of the approach was demonstrated for a sediment extract and a dust extract. In the sediment extract, PCDDs, PCDFs, PCAs and PCNs were identified and their efficient separation was achieved. In the dust sample, separation of PCAs and PBDEs was achieved and several new PBDE congeners were identified.     

Comprehensive two-dimensional gas chromatography in metabolomics

One of the major objectives in metabolomics is the identification of subtle changes in metabolite profiles as affected by genetic or environmental factors. Comprehensive two-dimensional gas chromatography (GC × GC) hyphenated to a fast-acquisition mass spectrometer is a well-established analytical technique to study the composition of complex samples due to its enhanced separation capacity, sensitivity, peak resolution, and reproducibility. This review reports applications of GC × GC to metabolomics studies of sample of different types (biofluid, cells, tissue, bacteria, yeast, plants), and discusses its advantages and limitations.     

Comprehensive two-dimensional gas chromatography in stop-flow mode

The theory and proof of concept of a new mode of operation for comprehensive two-dimensional gas chromatography (GC x GC) is presented. In current GC x GC interface designs, the modulation period defines the separation time allowed in the second dimension. In the stop-flow GC x GC mode, flow in the primary column is periodically stopped for brief periods of time. Consequently, the modulation period for the primary column and the amount of time available for second dimension separation become independent variables. This allows the separations in both the primary and secondary dimensions of the GC x GC system to be carried out under more optimised conditions, allowing extended periods of time for second dimension separations without sacrificing the separation in the primary dimension. This new technique has the potential to offer increased separation power and overall resolution as it is further developed.     

Separation and screening of short-chain chlorinated paraffins in environmental samples using comprehensive two-dimensional gas chromatography with micro electron capture detection

Short-chain chlorinated paraffins (SCCPs) are highly complex technical mixtures with thousands of isomers and numerous homologs. They are classified as priority candidate persistent organic pollutants under the Stockholm Convention for their persistence, bioaccumulation, and toxicity. Analyzing SCCPs is challenging because of the complexity of the mixtures. Chromatograms of SCCPs acquired using one-dimensional (1D) gas chromatography (GC) contain a large characteristic “peak” with a broad and unresolved profile. Comprehensive two-dimensional GC (GC×GC) shows excellent potential for separating complex mixtures. In this study, GC×GC coupled with micro electron capture detection (μECD) was used to separate and screen SCCPs. The chromatographic parameters, including the GC column types, oven temperature program, and modulation period, were systematically optimized. The SCCP congeners were separated into groups using a DM-1 column connected to a BPX-50 column. The SCCP congeners in technical mixtures were separated according to the number of chlorine substituents for a given carbon chain length and according to the number of carbon atoms plus chlorine atoms for different carbon chain lengths. A fish tissue sample was analyzed to illustrate the feasibility of the GC×GC–μECD method in analyzing biological samples. Over 1,500 compounds were identified in the fish extract, significantly more than were identified using 1D GC. The detection limits for five selected SCCP congeners were between 1 and 5 pg/L using the GC×GC method, and these were significantly lower than those achieved using 1D GC. This method is a good choice for analysis of SCCPs in environmental samples, exhibiting good separation and good sensitivity. Graphical Abstract

Chromatograms of a technical C10–C13 SCCP mixture with a 55 % (w/w) chlorine content obtained using a gas chromatography–electron capture detection (ECD) and b GC×GC–μECD     

On-line coupling of equilibrium-sorptive enrichment to gas chromatography to determine low-molecular-mass pollutants in environmental water samples

On-line combination of equilibrium sorptive enrichment and gas chromatography is used for the analysis of a group of pollutants varying widely in polarity and volatility in aqueous samples at trace levels. For the ESE process open-tubular traps were used. The newly developed hyphenated method shows a high sensitivity for all the compounds under study. The detection limits were typically between 0.1 and 1 microg/l. The sample volumes required for the compounds to reach equilibrium with the stationary phase are in the range of 20 ml for the aromatic hydrocarbons included in the study (benzene, toluene and p-xylene), to 200 ml for epichlorohydrin and dichlorohydrin. Within- and between-day precision of the absolute peak areas varied between 3 and 16%. The performance of the new method was tested by the analysis of different environmental water samples.     

Comprehensive two-dimensional gas chromatography of the 209 polychlorinated biphenyls

Comprehensive two-dimensional gas chromatography (GC x GC) of the 209 polychlorinated biphenyls (CBs) was carried out using a longitudinally modulated cryogenic system (LMCS) and liquid carbon dioxide as cryogen. The effluent from a non-polar column was modulated and further separated on either a polar or a shape-selective second-dimension column. Five GC x GC column combinations were evaluated, with DB-XLB as the first column in each case. DB-XLB separates more congeners than any other GC column currently available. When combined with a biscyanopropyl siloxane (SP-2340 or BPX70) or smectic liquid crystal (LC-50) second-dimension column in a GC x GC system many additional CBs can be separated. In total, 176 and 181 of the 209 congeners were separated (Rs = 0.5) on the column combinations DB-XLB/SP-2340 and DB-XLB/LC-50, respectively. Of the 136 CBs present in any Aroclor mixture at concentrations greater than 0.05% (w/w), 126 were resolved using either of these two column combinations. The seven frequently measured CBs 28, 52, 101, 118, 138, 153, 180, and the WHO-PCBs 77, 81, 105, 114, 118, 123, 126, 156. 157, 167, 169 and 189 were all separated from Aroclor CBs on the DB-XLB/LC-50 column set, whereas CBs 118 and 131 coeluted on the DB-XLB/SP-2340 column set. In addition, three technical CB formulations (Aroclors 1232, 1248 and 1260) and a seal blubber sample (Halichoerus grypus) from the Baltic Sea were analyzed. Similar peak patterns were found for Aroclor 1260 and the CBs in the seal blubber, facilitating use of this technical CB formulation to identify the CBs in the blubber by GC x GC. Individual CBs in environmental samples, such as seal blubber, may be identified semi-automatically by matching the samples GC x GC profiles to a template generated using a standard containing all 209 CBs. Using such a template, 64 CBs were identified in the grey seal blubber sample.     

Comprehensive two-dimensional gas chromatography of polybrominated diphenyl ethers

Comprehensive two-dimensional gas chromatography with micro electron-capture detection (GCxGC-muECD) was evaluated for the separation of 125 polybrominated diphenyl ethers (PBDEs). From among the six column combinations that were evaluated, DB-1x007-65HT was found to be the most suitable because of: (i) the highest number of BDE congeners separated; (ii) the least decomposition of higher brominated congeners; and (iii) the most suitable maximum operating temperature. The separation of the 125 BDE congeners from five hydroxy- and two methoxy-BDEs and nine other brominated flame retardants (polybrominated biphenyls, tetrabromobisphenol-A, methyl-tetrabromobisphenol-A and hexabromocyclododecane) was also studied. Fluorinated BDEs were found to be valuable internal standards for the determination of BDEs because of their very similar physico-chemical properties and excellent separation from the parent BDEs, mainly in the second dimension. GCxGC-time-of-flight MS and GCxGC-muECD were shown to be useful tools to identify decomposition products of nona- and deca-substituted BDEs, which are formed during the GC run. Three nona-BDEs were shown to be the major decomposition products of BDE 209.     

Comprehensive two-dimensional gas chromatography in the analysis of dietary fatty acids

Comprehensive two-dimensional gas chromatography utilising a semi-rotating cryogenic modulator was applied to the analysis of dietary milk derived fatty acids. Four column combinations were tested: two polar-nonpolar and two different nonpolarpolar column combinations. Best results were obtained with a nonpolar-polar column set, with narrow-bore (50 microm ID) Carbowax column as the second column. The GC x GC method clearly improved the separation efficiency of the fatty acids in comparison with one-dimensional GC analysis and proved to be suitable for the quantification of the analytes. The relative standard deviations (RSD) of the retention times in the first and second dimensions were on average 0.06% and 4.9%, respectively. The relative RSD for peak volumes was on average 2.9%.     

Comprehensive two-dimensional gas chromatography applied to illicit drug analysis

Multidimensional gas chromatography (MDGC), and especially its latest incarnation—comprehensive two-dimensional gas chromatography (GC × GC)—have proved advantageous over and above classic one-dimensional gas chromatography (1D GC) in many areas of analysis by offering improved peak capacity, often enhanced sensitivity and, especially in the case of GC × GC, the unique feature of ‘structured’ chromatograms. This article reviews recent advances in MDGC and GC × GC in drug analysis with special focus on ecstasy, heroin and cocaine profiling. Although 1D GC is still the method of choice for drug profiling in most laboratories because of its simplicity and instrument availability, GC × GC is a tempting proposition for this purpose because of its ability to generate a higher net information content. Effluent refocusing due to the modulation (compression) process, combined with the separation on two ‘orthogonal’ columns, results in more components being well resolved and therefore being analytically and statistically useful to the profile. The spread of the components in the two-dimensional plots is strongly dependent on the extent of retention ‘orthogonality’ (i.e. the extent to which the two phases possess different or independent retention mechanisms towards sample constituents) between the two columns. The benefits of ‘information-driven’ drug profiling, where more points of reference are usually required for sample differentiation, are discussed. In addition, several limitations in application of MDGC in drug profiling, including data acquisition rate, column temperature limit, column phase orthogonality and chiral separation, are considered and discussed. Although the review focuses on the articles published in the last decade, a brief chronological preview of the profiling methods used throughout the last three decades is given.     

Comprehensive two-dimensional gas chromatography for the analysis of Fischer-Tropsch oil products

The Fischer-Tropsch (FT) process involves a series of catalysed reactions of carbon monoxide and hydrogen, originating from coal, natural gas or biomass, leading to a variety of synthetic chemicals and fuels. The benefits of comprehensive two-dimensional gas chromatography (GC×GC) compared to one-dimensional GC (1D-GC) for the detailed investigation of the oil products of low and high temperature FT processes are presented. GC×GC provides more accurate quantitative data to construct Anderson-Schultz-Flory (ASF) selectivity models that correlate the FT product distribution with reaction variables. On the other hand, the high peak capacity and sensitivity of GC×GC allow the detailed study of components present at trace level. Analyses of the aromatic and oxygenated fractions of a high temperature FT (HT-FT) process are presented. GC×GC data have been used to optimise or tune the HT-FT process by using a lab-scale micro-FT-reactor.     

Comprehensive two-dimensional gas chromatography analysis of high-ethanol containing motor fuels

A comprehensive 2-D GC (GC x GC) instrument equipped with a flow-switching modulator was used to determine the concentration of ethanol and eight other alcohols in a retail pump sample of E85 fuel. E85 is a mixture of ethanol and gasoline where the ethanol concentration can range from 70 to 85 vol%. The increased peak capacity and selectivity generated by GC x GC analysis allowed the alcohols to be fully resolved from the gasoline hydrocarbons. GC x GC analysis was compared to the performance obtained with the standard analytical method for determining ethanol in fuel ethanol (ASTM D5501) and the standard method for determining oxygenate concentrations in gasoline (ASTM D4815). The GC x GC analysis required 14 min while the combined ASTM D5501 and ASTM D4815 analyses required more than 60 min. The ethanol concentration obtained by GC x GC was in excellent agreement with the value obtained by the D5501 method. Poorer agreement was observed between the GC x GC and D4815 concentrations for the other alcohols present in E85. In all cases, the differences could be attributed to deficiencies in the D4815 method that led to coelutions between the alcohols and gasoline hydrocarbons.     

Dynamic ultrasound-assisted extraction of environmental pollutants from marine sediments for comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometric detection

A dynamic ultrasound-assisted extraction (UAE) of marine sediments has been optimized using experimental design methodology. Comprehensive two-dimensional gas chromatography (GC x GC) using a cryogenic modulator, and time-of-flight-mass spectrometry (TOF-MS) were used to separate and identify environmental pollutants. Six compounds from three different chemical classes were used to optimize the extraction parameters.     

Improved screening analysis of organic pollutants in river water samples by gas chromatography with atomic emission detection (GC-MIP-AED)

 The potential of gas chromatography with a microwave-induced plasma atomic emission detector (GC-MIP-AED) for the screening analysis of trace organic components in river water samples is presented. The application of a commercially available GC-MIP-AED system to the screening of organic trace compounds has been greatly enhanced by the optimisation of the operating parameters to achieve the highest sensitivity for the simultaneous determination of C, H, Cl, Br, S and N. An improved evaluation of the chromatographic data has been carried out using several new self-developed macros, which allow the calculation of elemental response ratio factors (RRFs) and empirical formulas for the analysed compounds at different concentration levels. A significant dependence of the RRFs on the concentration level was found for hydrogen and sulphur, whereas the dependence of the RRFs on the type of compound is not significant, considering the analytical objective. Limits of detection in the pg-range can be obtained for the elements investigated. The calculation of empirical formulas and its precision is shown for several analytes over a wide range of concentration. At a concentration level close to the limit of detection the error of the formula calculation increases significantly. The performance characteristics of the GC-MIP-AED system in the presence of matrix interferences are assessed by measuring spiked river water samples. Received: 29 July 1996 / Revised: 12 October 1996 / Accepted: 24 October 1996     

Comprehensive two-dimensional gas chromatography to characterize hydrocarbon mixtures in lithic materials

The analysis of organic biomarkers in chert samples offers key information about the environmental conditions in which these samples were formed, and this information can be used to track the lithic materials of many archaeological artifacts. Since the content of the organic fraction is very low and the complexity of the organic extracts is quite high, we have optimized the GC×GC separation of these mixtures. Making use of mixture of C(16)H(34)-C(44)H(90)n-alkane standards, a central composite design was carried out taking into account the carrier flow in the first and second columns, the modulation period and the discharge time. Regarding the measured responses, though the initially considered one was the peak volume, we have also evaluated the effects on the number of modulated peaks per analyte, the symmetry of the modulated peaks and the number of detected compounds. The final optimum conditions were defined as follows: a hydrogen flow of 1.2 mL/min in the first column and 18 mL/min in the second one, a modulation period of 1.4 s and a discharge time of 0.1 s and under these conditions all the response variables showed optimum values. Based on this optimized method several chert samples obtained from different stratigraphic levels in an ancient quarry were studied and we were able to distinguish them on the basis of the different constituents of organic biomarkers, such as mono-methylated alkanes, cyclic n-alkanes, branched alkanes, steranes and hopanes.     

全二维气相色谱技术在痕量污染物分析中的应用进展

随着环境保护的深入及对污染物低剂量长期暴露风险认知度的提高,开发高灵敏、高准确的污染物检测技术是环境监测的重要发展方向之一。由于某些污染物组成的多样性和复杂性,对准确定量分析环境介质中微量乃至痕量污染物提出了很大的挑战。本文以近期发表在主要国际刊物的几个工作为典型案例,介绍了全二维气相色谱技术在痕量污染物分析中的应用进展     

Comprehensive two-dimensional gas chromatography: metrics,potentials, limits

Metrics for evaluation of separation performance of comprehensive two-dimensional gas chromatography (GCxGC) and for quantitative comparison of that performance with similar performance of its 1D (one-dimensional) counterparts are described. The performance improvement can be expressed via reduction in the saturation of a chromatogram or-in the case of the uniform distribution of peaks along the second dimension--via the peak capacity gain due to GCxGC. An order of magnitude peak capacity gain due to the comprehensive GCxGC is possible under optimal conditions. Optimal parameters of the second dimension column as well as the optimal operational conditions for that column and for the modulator in a comprehensive GCxGC are also presented.