Evaluation of Alkyl Bonded Silica and Solvent Phase Modifiers for the Efficient Elution of Basic Drugs on HPLC

Abstract

Nine representative drugs were used to evaluate the effects of alkyl bonded stationary phases containing type A and type B silica and the effects of an amine modifier on the efficiency of high performance liquid chromatographic elution of basic and acidic drugs. The theoretical plate count and asymmetry factor of the eluted peaks were compared to that of acetophenone as a reference to the maximal efficiency of each system evaluated. Zorbax^R C₈ was used as the stationary phase prepared from type A silica and Zorbax RX^R was used as the stationary phase prepared from the type B silica. The theoretical plate count and asymmetry factor of acetophenone was observed to be the same on both columns when analyzed in an acidic aqueous/acetonitrile mobile phase. An improvement in the efficiency and peak shape of the amine containing compounds was observed using the Zorbax RX^R stationary phase as compared to the efficiency and peak shape of these compounds on the Zorbax^R C₈ stationary phase. Interestingly, the acidic compounds salicylic acid and mefenamic acid showed better peak shapes on the Zorbax RX^R column than on the Zorbax C₈. For all drugs studied the theoretical plate count and asymmetry factor was better on both the Zorbax^R C₈ and the Zorbax RX^R stationary phases when the amine modifier triethylamine was used in the mobile phase. Except for salicylic acid, the theoretical plate count and asymmetry factor for each drug was similar on the Zorbax^R C₈ and the Zorbax RX^R columns when the amine modifier