Page 63 - Chiral Separation Techniques

2.3 Method Development with Glycopeptide CSPs 39

Fig. 2-6. Method development protocols on 250 × 4.6 mm glycopeptide columns. V: vancomycin,
T: teicoplanin, R: ristocetin A.

2.3.2 Column Coupling Technique

The direct coupling of two columns through a low dead volume connector is cur-
rently a common and useful practice. The coupled columns are used with the same
mobile phase conditions. Various kinds of combinations have been made to directly
couple columns of similar or distinctive selectivities. A standard reversed-phase
(C ) column, for example, has been coupled with: a cyano column [21], molecularly
18
imprinted polymer [22], phenyl [23], C [24], and silica [25] columns in order to
8
achieve broader selectivity. For the analysis of a mixture containing one or more chi-
ral analytes, the column coupling becomes more important. While a chiral column is
designed to resolve optical isomers, its performance was enhanced and lifetime
increased by coupling it with an achiral column [26]. A variety of chiral pharma-
ceuticals were enantiolresolved and separated from impurities or their metabolites in
human plasma by coupling achiral columns with polymeric chiral stationary phases