COMPARISON OF SEPARATION SELECTIVITY IN AQUEOUS AND NONAQUEOUS CAPILLARY ELECTROPHORESIS

The use of non-aqueous capillary electrophoresis in free solution in u ncoated fused-silica capillaries was investigated and compared with ca pillary electrophoresis using aqueous systems. Cationic drug substance s differing only in the amine functionallity or even having the same c harge-to-mass ratio were used as test solutes. Some of these test subs tances are difficult to separate in plain aqueous buffers and even whe n using micellar electrokinetic chromatography or by adding cyclodextr ins to the electrophoresis buffer it is difficult to obtain baseline s eparations. Very high separation selectivity may be obtained in non-aq ueous capillary electrophoresis systems without adding surfactants or complexing agents to the electrophoresis medium. Major selectivity cha nges may be obtained using different organic solvents (formamide, N-me thylformamide, N,N-dimethylformamide, N,N-dimethyiacetamide, dimethyl sulfoxide, methanol and acetonitrile) for the electrophoresis medium, e.g., the relative electrophoretic mobilities of a primary, a secondar y and a tertiary amine with otherwise identical structures are reverse d on replacing acetonitrile with methanol as solvent.