Chromatographic separation multi-dimensionality

Dixon, S.P., Pitfield, I.D., Perrett, D. (2006). Comprehensive multi-dimensional liquid chromatographic separation in biomedical and pharmaceutical analysis a review. Biomed. Chromatogr. 20, 508-529. 

Interferences caused by inadequate chromatographic separation during the final determination (e.g., no prior group separation of PCBs or OCPs). This can be improved by multi-dimensional GC or multi-dimensional preparative LC. 

Multi-dimensional Chromatography. Multi-dimensional chromatography is the term used to describe a variety of methods where fractions from one chromatographic system are each transferred to another for further separation. Combinations of SEC with thin-layer chrcmatography have been shown to enable separation of copolymers by composition in a "cross-fractionation". OC utilizes a combination of two SECs in a cross-fractionation approach. 

In this respect, selective sampling techniques coupling different kinds of chromatographic processes such as multi-dimensional g.c. or separation on microcolumns seem to be promising. 

Instead by solvent extraction [207], aroma compounds from aqueous media, e.g. fruit juices, can even be separated and enriched by techniques of solid phase micro extraction (SPME), preferably from the headspace [208] , corresponding devices can often be directly connected to GC systems. These techniques provide the complete spec-tmm of the individual compounds of an aroma. As it will normally not be possible and even not necessary to analyse all components of the complex mixture, the separation of its main compounds may demand a multi-dimensional (MD) gas chromatographic system [209[ as displayed in Fig. 6.14 [210[. Examples for the multi-ele-ment/multi-compound isotope analysis by such systems will be given later (6.2.2.4.4, [211[) they can even integrate the identification of the compounds by molecular mass spectrometry and a simultaneous determination of the enantiomer ratios of isomers [210, 211 [. The importance of enantiomer analysis as a tool for authenticity assessment is extensively treated in chapter 6.2.3. 

Tabun, Sarin, Soman, DPP, and VX, organophosphorus warfare compounds, were detected and determined by OPLC in the presence of 20 different types of pesticides such as OC, OP, carbamates, and carbamides. The determination of these compounds was disturbed by the structurally related OP insecticides. The chromatographic separation was studied by two dimensional TLC. The multi-component eluent system was optimiz by the PRISMA model. 

True multi-dimensional chromatography requires two independent (orthogonal) separations mechanisms and the conservation of the first separation into the second dimension. Comprehensive GC X GC today is the most developed and most powerful multi-dimensional chromatographic technique. The technique has been widely accepted and applied to the analysis of complex mixtures. Commercial instrumentation is available at a mature technological standard for routine application (Figure 2.132). 

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