Chromatographic mode selection

The chromatographic mode selected for analytical separations depends upon the extraction and cleanup procedures employed and the vitamers required to be measured. 

The aim of this chapter is to evaluate the orthogonality of selected 2DLC systems for the separation of peptides. The orthogonality of different chromatographic modes was quantitatively characterized using a novel geometric approach. Practical peak capacity was calculated from the theoretical peak capacity and the knowledge of... 

TABLE 12.1 Chromatographic Modes and Conditions Used for LC-MS Study of Tryptic Peptides Separation Selectivity... 

Total theoretical peak capacity for the ID and 2D LC/MS analyses of the yeast ribosomal protein sample was calculated as 240 and 700, respectively. Individual separation peak capacities were calculated by dividing the total separation time by the average peak width at baseline, and the 2D peak capacity determined as the product of the peak capacity of the two dimensions. These theoretical calculations rely on optimal use of the two-dimensional separation space, which in turn is dependent upon the lack of correlation between the component retention times in the two separation modes. Thus, the maximum use of the theoretical peak capacity is not only dependent on the selection of chromatographic modes based on different physicochemical... 

Selection of eluting solvent is based on knowledge of the eluting strength e° of the solvent in the chromatographic mode. 

While HPLC does not always produce superior results to those with TLC it allows greater versatility and is more suitable for the analysis of complex organic matrices such as cereals. HPLC coupled to sensitive detection and sophisticated data retrieval has improved the identification of selected mycotoxins at levels much less than achieved by TLC. Additional chromatographic modes such as normal-phase, reverse phase and ion-exchange chromatography have been employed. There are no truly universal detectors available for HPLC. Detectors presently in use include Fourier transform infrared detections (FT-IRD), diode array ultraviolet detection (DAD) and mass selection detectors (MSD) (Coker, 1997). 

Possibility of full automation Greater precision and accuracy Improvement in selectivity by combining different chromatographic modes Minor consumption of organic solvents Protection of photolabile analytes precolumn... 

The selectivity a of all chromatographic modes can be defined as the relative separation achieved between adjacent solute peaks and thus reflects the overall performance in relative selectivity of a chromatographic system. In particular, selectivity a is given by the ratio of capacity factors for adjacent peaks Pj and , i.e.,... 

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