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

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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. ZorbaxR C8 was used as the stationary phase prepared from type A silica and Zorbax RXR 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 RXR stationary phase as compared to the efficiency and peak shape of these compounds on the ZorbaxR C8 stationary phase. Interestingly, the acidic compounds salicylic acid and mefenamic acid showed better peak shapes on the Zorbax RXR column than on the Zorbax C8. For all drugs studied the theoretical plate count and asymmetry factor was better on both the ZorbaxR C8 and the Zorbax RXR 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 ZorbaxR C8 and the Zorbax RXR columns when the amine modifier