Multidimensional gas

Making a detailed estimate of the full loading of an object by a blast wave is only possible by use of multidimensional gas-dynamic codes such as BLAST (Van den Berg 1990). However, if the problem is sufficiently simplified, analytic methods may do as well. For such methods, it is sufficient to describe the blast wave somewhere in the field in terms of the side-on peak overpressure and the positive-phase duration. Blast models used for vapor cloud explosion blast modeling (Section 4.3) give the distribution of these blast parameters in the explosion s vicinity. 

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

H. Tani and M. Furuno, Rapid analysis of hydrocarbons and inert gases hy a multidimensional gas cltromatograph , J. High Resolut. Chromatogr. Chromatogr. Commun. 9 712-716(1985). 

J. J. Szakasits and R. E. Robinson, Hydrocarbon type determination of naphthas and catalytically reformed products hy automated multidimensional gas cliromatography . Anal. Chem. 63 114-120(1991). 

M. Heiraiz, G. Reglero, T. Heiraiz and E. Loyola, Analysis of wine distillates made from muscat grapes (Pisco) by multidimensional gas cliromatography and mass spec-ti ometry , J. Agric. Food Chem. 38 1540-1543 (1990). 

A. Mosandl, K. Eischer, U. Hener, P. Kieis, K. Rettinger, V. Schubert and H.-G. SchmaiT, Stereoisomeiic flavor compounds. 48. Cliirospecific analysis of natural flavor s and essential oils using multidimensional gas cliromatography , ]. Agric. Food Chem. 39 1131-1134(1991). 

C. Askaii, U. Hener, H-G. Sclimair, A. Rapp and A. Mosandl, Stereodifferentiation of some chkal monoteipenes using multidimensional gas cliromatography , Fresenius J. Anal. Chem. 340 768-772 (1991). 

V. Karl, H-G. Schmair and A. Mosandl, Simultaneous stereoanalysis of 2-alkyl-branched acids, esters and alcohols using a selectivity-adjusted column system in multidimensional gas cliromatography , 7. Chromatogr. 587 347-350(1991). 

S. Nitz, B. Weinreich and F. Draweit, Multidimensional gas cliromatography-isotope ratio mass spectrometry (MDGC-IRMS). Part A system description and technical requirements , 7. High Resolut. Chromatogr. 15 387-391 (1992). 

E. Benicka, R. Novakovsky, J. Hrouzek, J. Krtipcfk, P. Sandra and J. de Zeeuw, Multidimensional gas cliromatogr aphic separation of selected PCB atr opisomers in technical formulations and sediments , 7. High Resolut. Chromatogr. 19 95-98 (1996). 

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. 

K. A. Rrock, N. Ragunathan and C. L. Wilkins, Parallel cryogenic rtapping multidimensional gas cliromatography with directly linked infrared and mass specrtal detection , ]. Chmmatogr. 645 153-159 (1993). 

T. Tiuong, P. J. Maiiiott and N. A. Porter, Analytical study of comprehensive and tai -geted multidimensional gas cliromatogi aphy incorporating modulated cryogenic capping , J. AOAC Int. submitted (2000). 

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. 

Mondello et al. (2, 20-23) have used a multidimensional gas chromatographic system based on the use of mechanical valves which were stable at high temperatures developed in their laboratory for the determination of the enantiomeric distribution of monoterpene hydrocarbons (/3-pinene, sabinene and limonene) and monoterpene alcohols (linalol, terpinen-4-ol and a-terpineol) of citrus oils (lemon, mandarin, lime and bergamot). Linalyl acetate was also studied in bergamot oil. The system consisted of two Shimadzu Model 17 gas chromatographs, a six-port two-position valve and a hot transfer line. The system made it possible to carry out fully... 

Figure 10.4 Schematic representation of the multidimensional GC-IRMS system developed by Nitz et al. (27) PRl and PR2, pressure regulators SV1-SV4, solenoid valves NV— and NV-I-, needle valves FID1-FID3, flame-ionization detectors. Reprinted from Journal of High Resolution Chromatography, 15, S. Nitz et al, Multidimensional gas cliro-matography-isotope ratio mass specti ometiy, (MDGC-IRMS). Pait A system description and teclinical requirements , pp. 387-391, 1992, with permission from Wiley-VCFI.

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). 

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). 

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). 

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

Figure 13.2 MDGC-ECD chromatograms of PCB fractions from sediment samples, demonstrating the separation of the enantiomers of (a) PCB 95, (b) PCB 132, and (c) PCB 149 non-labelled peaks were not identified. Reprinted from Journal of Chromatography, A 723, A. Glausch et al, Enantioselective analysis of chiral polyclilorinated biphenyls in sediment samples by multidimensional gas cliromatography-electi on-capture detection after steam distillation-solvent exti action and sulfur removal , pp. 399-404, copyright 1996, with permission from Elsevier Science.

K. A. Rrock and C. L. Wilkins, Qualitative analysis of contaminated environmental extracts by multidimensional gas cliromatography with infrared and mass specti al detection (MDGC-IR-MS) , pp. 167-178, copyright 1996, with permission from Elsevier Science. 

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