Mixed chiral stationary phases for chromatography

Abstract

Mixed stationary phases for the separation of enantiomers make possible to increase the universality
of the chiral phase. They are used in liquid and gas chromatography. Mixed chiral selectors for gas chromatography are most often β-cyclodextrin derivatives, less often amino acid derivatives. In gas chromatography mixtures of modified β-cyclodextrins are widely and successfully used to separate the enantiomers of substances found in essential oils of plants and fruit, as well as N-trifluoroacetyl-ethyl esters of amino acids. An averaged effect is often observed from each component of mixed chiral phase, but in some cases a synergistic effect is detected by the authors. Mixed chiral selectors with low molecular weight selectors, derivatives of polysaccharides, proteins and macrocyclic antibiotics are most researched by HPLC. The combination of selectors in the stationary phase is determined largely by two factors: the ability to complement each other's enantioselective properties and the similarity of their immobilization on the matrix (most often it is silica gel). Chiral phase with human serum albumin and α1-glycoprotein allows you to separate the optical isomers of the cationic, anionic and neutral compounds, among them more than ten pharmaceutical drugs. Binary chiral selectors containing cellulose tris-benzoate, cellulose tris-(4-methylphenylcarbinol), cellulose tris-phenylcarbamate, cellulose tris(4-chlorpheniramine) and amylose tris-(3,5-dimethylphenylcarbamate) were also investigated. As a rule, mixed stationary phases have an average ability to separate enantiomers as compared to phases with a single chiral selector, but enantioselectivity is increased in some cases. It is important, that these phases could be analyzed by a 100 % ethanol mobile phase. It is considered that a mixture of macrocyclic antibiotics (eremomycin and vancomycin) allows us to separate enantiomers of β-blockers and non-derivatized amino acids.
Vancomycin separates enantiomers of β-blockers only, eremomycin separates amino acids enantiomers. The
combination of eremomycin and bovine serum albumin (BSA) slightly changes the selectivity of enantiomer
separation of profens. BSA on the sorbent surface eliminates the influence of proteins in the sample solution
on profens determination. It simplifies a sample preparation during the analysis of biological fluids.