Chromatographic methods multidimensional

MULTIDIMENSIONAL CHROMATOGRAPHIC METHODS WHICH INVOLVE THE USE OF SUPERCRITICAL FLUIDS... 

Multidimensional chromatography has important applications in environmental analysis. Environmental samples may be very complex, and the fact that the range of polarity of the components is very wide, and that there are a good many isomers or congeners with similar or identical retention characteristics, does not allow their separation by using just one chromatographic method. 

In order to reduce or eliminate off-line sample preparation, multidimensional chromatographic techniques have been employed in these difficult analyses. LC-GC has been employed in numerous applications that involve the analysis of poisonous compounds or metabolites from biological matrices such as fats and tissues, while GC-GC has been employed for complex samples, such as arson propellants and for samples in which special selectivity, such as chiral recognition, is required. Other techniques include on-line sample preparation methods, such as supercritical fluid extraction (SFE)-GC and LC-GC-GC. In many of these applications, the chromatographic method is coupled to mass spectrometry or another spectrometiic detector for final confirmation of the analyte identity, as required by many courts of law. 

In general, a comprehensive separation strategy implies the desire to resolve/analyze all components within a sample. In the specific context of a multidimensional chromatographic method, the term is more narrowly applied to indicate that all analytes introduced to the first-dimension separation are also subjected to a second-dimension separation. There are two basic configurations used by our laboratory to carry out comprehensive multidimensional (IEX/RP) protein separations—IEX— Dual Column RP system and IEX—Dual Trap RP system (Figs. 13.1 and 13.2), respectively. 

R. A. Kenley, S. Chandry, and G. A. Visor, Multidimensional column-switching liquid chromatographic method for dissolution testing of enprostil soft elastic gelatin capsules, J. Pharm. Sci., 75 999 (1986). 

Multidimensional chromatography separations are currently one of the most promising and powerful methods for the fractionation and characterization of complex sample mixtures in different property coordinates. This technique combines extraordinary resolution and peak capacity with flexibility, and it overcomes the limitations of any given single chromatographic method. This is the ideal basis for the identiflcation and quantification of major compounds and by-products, which might adversely affect product properties if not detected in time. 

Dunayevskiy and Hughes [84] proposed the ultimate in multidimensional chromatographic methods for the screening of drug candidates noncovalently bound to receptors by combining serially GPC, ultrafiltration, and RP-HPLC... 

Multidimensional chromatographic separation can be accomplished by coupling two separation dimensions based on the same chromatographic method (e.g., GC-GC or HPLC-HPLC), or by coupling two different methods (e.g., HPLC-GC or HPLC-SFC). Following is a brief overview of the most popular two-dimensional separation techniques. 

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