Gas chromatography multidimensional

Principles and Characteristics Multidimensional gas chromatography (MDGC) is widely used, due to the mobile-phase compatibility between the primary and secondary separating systems, which allows relatively simple coupling with less-complicated interfaces. In its simplest form, 2DGC can be carried out in the off-line mode. The most elementary procedure involves manual collection of effluent from a column, followed by reinjection into another column of a different selectivity (e.g. from an apolar to a polar column). Selecting proper GC-column combinations is critical. In on-line mode, the interface in MDGC must provide for the quantitative transfer of the effluent from one column 

GC-TLC is not particularly difficult, but has been little used since its inception in the mid-1960s [907-912]. In most instances TLC was used to either confirm the 

As for sample preparation, SPE-GC has become more popular than NPLC-GC. Aqueous samples are not compatible with NPLC-GC, while RPLC-GC has never become a success. SPE-GC-(tandem)MS and SPE-GC-AED systems have demonstrated excellent performance. SPME is an equilibrium technique while SPE affords exhaustive extraction of the analytes. Laser desorption injection in LD-GC-MS can uniquely provide an additional dimension of spatial information for 2D surface chemical mapping [221]. 

MDGC and GCxGC have recently been reviewed [917-921a], 

GCxGC is most often applied for target analysis. Main application areas for GCxGC are to be found where unresolved peaks are the norm, i.e. for atmospheric organics (e.g. urban air), food and flavour (organoleptics), (petro)chemical and forensic analyses, 

In general, capillary gas chromatography provides enough resolution for most determinations in environmental analysis. Multidimensional gas chromatography has been applied to environmental analysis mainly to solve separation problems for complex groups of compounds. Important applications of GC-GC can therefore be found in the analysis of organic micropollutants, where compounds such as polychlorinated dibenzodioxins (PCDDs) (10), polychlorinated dibenzofurans (PCDFs) (10) and polychlorinated biphenyls (PCBs) (11-15), on account of their similar properties, present serious separation problems. MDGC has also been used to analyse other pollutants in environmental samples (10, 16, 17). 

MDGC has also been used in the air analysis field. For instance, it has been applied to the analysis of volatile organic compounds (VOCs) in air, thus enabling a wider range of these compounds to be analysed (18). 

however, GC-GC coupling is seldom used to determine pesticides in environmental samples (2), although comprehensive MDGC has been applied to determine pesticides in more complex samples, such as human serum (19). On the other-hand, new trends in the pesticide market, which is now moving towards the production of optically active enantiomers and away from racemic mixtures, may make this area suitable for GC-GC application. The coupling of non-chiral columns to chiral columns appears to be a suitable solution to the separation problems that such a trend might cause. 

Multidimensional gas chromatography has also been used in the qualitative analysis of contaminated environmental extracts by using spectral detection techniques Such as infrared (IR) spectroscopy and mass spectrometry (MS) (20). These techniques produce the most reliable identification only when they are dealing with pure substances this means that the chromatographic process should avoid overlapping of the peaks. 

Most applications in environmental analysis involve heart-cut GC-GC, while comprehensive multidimensional gas chromatography is the most widely used technique for analysing extremely complex mixtures such as those found in the petroleum industry (21). 

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W. Beitsch, Multidimensional gas chromatography , in Multidimensional Chromatography. Techniques and Applications, H. J. Cortes (Ed.), Marcel Dekker, New York, pp. 75-110 (1990). 

Conventional multidimensional gas chromatography operation procedures should now be reconsidered and redefined in light of the new method of comprehensive GC X GC technology, as discussed below. 

Accepting that the cryofocussing/remobilization process is both effective in the collection of discrete sections of the effluent from column 1, and very rapid in reinjection to column 2, we can now propose a number of ways of using the LMCS device in multidimensional gas chromatography modes. 

GC using chiral columns coated with derivatized cyclodextrin is the analytical technique most frequently employed for the determination of the enantiomeric ratio of volatile compounds. Food products, as well as flavours and fragrances, are usually very complex matrices, so direct GC analysis of the enantiomeric ratio of certain components is usually difficult. Often, the components of interest are present in trace amounts and problems of peak overlap may occur. The literature reports many examples of the use of multidimensional gas chromatography with a combination of a non-chiral pre-column and a chiral analytical column for this type of analysis. 

Reprinted from Journal of High Resolution Chromatography, 21, D. Juchelka et al., Multidimensional gas chromatography coupled on-line with isotype ratio mass specti ometry (MDGC-IRMS) progress in the analytical authentication of genuine flavor components , pp. 145-151, 1998, with peraiission from Wiley-VCH. 

A. Mosandl, U. Hener, U. Hagenauer-Hener and A. Kuster mann, Stereoisomeric flavor compounds. 33. Multidimensional gas chromatography dkect enantiomer separation of -y-lactones from fr uits, foods and beverages , 7. Agric. Food Chem. 38 767-771 (1990). 

V. Schubert, R. Diener and A. Mosandl, Enantioselective multidimensional gas chromatography of some secondary alcohols and their acetates from banana , Z C. Naturforsch. C. 46 33-36 (1991). 

EXAMPLES OE MULTIDIMENSIONAL GAS CHROMATOGRAPHY APPLIED TO ENVIRONMENTAL ANALYSIS... 

J. C. Duinker, D. E. Schult and G. Petiick, Multidimensional gas chromatography with electi on capture detection for the deteimination of toxic congeners in polycWorinated biphenyl mixture . Anal. Chem. 60 478-482 (1998). 

J. J. Szakasits and R. E. Robinson, Hydrocar bon type deter mination of naphthas and cat-alytically refor med products by automated multidimensional gas chromatography . Anal. Chem. 63 114-120(1991). 

Figure 15.8 Multidimensional GC-MS separation of urinary acids after derivatization with methyl chloroformate (a) pre-column cliromatogram after splitless injection (h) Main-column selected ion monitoring cliromatogram (mass 84) of pyroglutamic acid methyl ester. Adapted from Journal of Chromatography, B 714, M. Heil et ai, Enantioselective multidimensional gas chromatography-mass spectrometry in the analysis of urinary organic acids , pp. 119-126, copyright 1998, with permission from Elsevier Science.

Figure 15.9 Use of heart-cutting for the identification of target compounds in 90% evaporated gasoline. Peak identification is as follows 1, 1,2,4,5-teti amethylbenzene 2, 1,2,3,5-teti amethylbenzene 3, 4-methylindane 4, 2-methylnaphthalene 5, 5-methylindane 6, 1-methylnaphthalene 7, dodecane 8, naphthalene 9,1,3-dimethylnaphthalene. Adapted from Chromatography, 39, A. Jayatilaka and C.F. Poole, Identification of petroleum distillates from fire debris using multidimensional gas chromatography , pp. 200-209, 1994, with permission from Vieweg Publishing.

Authenticity evaluation has recently received increased attention in a number of industries. The complex mixtures involved often require very high resolution analyses and, in the case of determining the authenticity of natural products, very accurate determination of enantiomeric purity. Juchelka et al. have described a method for the authenticity determination of natural products which uses a combination of enantioselective multidimensional gas chromatography with isotope ratio mass spectrometry (28). In isotope ratio mass spectrometry, combustion analysis is combined with mass spectrometry, and the ratio of the analyte is measured versus a... 

Figure 15.10 Primary (a) and secondary (b) separation of unleaded gasoline, where (a) shows the IRD chromatogram, and (b) shows the MSD total ion chromatogram of heart cut c. Adapted from Analytical Chemistry, 65, N. Ragunathan et al., Multidimensional gas chromatography with parallel cryogenic tr aps , pp. 1012-1016, copyright 1993, with permission from the American Chemical Society.

Figure 15.11 (a) Total ion clnomatogram of a Grob test mixture obtained on an Rtx-1701 column, and (b) re-injection of the entire clnomatogram on to an Rtx-5 column. Peak identification is as follows a, 2,3-butanediol b, decane c, undecane d, 1-octanol e, nonanal f, 2,6-dimethylphenol g, 2-ethylhexanoic acid h, 2,6-dimethylaniline i, decanoic acid methyl ester ], dicyclohexylamine k, undecanoic acid, methyl ester 1, dodecanoic acid, methyl ester. Adapted from Journal of High Resolution Chromatography, 21, M. J. Tomlinson and C. L. Wilkins, Evaluation of a semi-automated multidimensional gas chromatography-infrared-mass specti ometry system for initant analysis , pp. 347-354, 1998, with permission from Wiley-VCH. 

A. Jayatilaka and C. E. Poole, Identification of peti oleum distillates from fire debris using multidimensional gas chromatography , Chromatographia 39 200-209 (1994). 

N. Ragunathan, K. A. Rrock and C. L. Wilkins, Multidimensional gas chromatography with parallel ayogenic traps , Chem. 65 1012-1016 (1993). 

M. J. Tomlinson and C. L. Wilkins, Evaluation of a semi-automated multidimensional gas chromatography-infared-mass spectrometry system for initant analysis , ]. High Resolut. Chromatogr. 21 347-354 (1998). 

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