Use of corrected retention indices based on 1-nitroalkane and alkyl arylketone scales for HPLC identification of basic drugs.

Sixteen basic drugs were examined by HPLC (gradient elution in acetonitrile/phosphate buffer, pH 3.2, containing 0.05% nonylamine) with six different ODS-silica columns. The retention indices (RI) were calculated with alkyl arylketone and 1-nitroalkane scales and were subjected to correction, which enabled comparison of results from commercially different column packing materials. The correction procedure was successful for the 1-nitroalkane scale. The scale based on alkyl arylketones was of less use for basic drugs, because some of them eluted earlier than the first reference homologue. This made impossible the proper calculation and correction of RI values for drugs such as cocaine, diphenhydramine, doxepin, and promethazine. The correction procedure of RI values calculated against the series of 1-nitroalkanes is recommended as a method of standardization of HPLC data.