International collaborative study of the retention reproducibility of basic drugs in high-performance liquid chromatography on a silica column with a methanol-ammonium nitrate eluent.

An international collaborative study between 10 laboratories has been carried out to study the reproducibility of the separation of basic drugs on silica columns. The laboratories used common solutions of drugs on both a common batch of packing material and different batches of the same brand of packing material. These were also compared with separations on other brands of packing material. Variations within-batch, within-brand and between brands have been compared. The retentions of the drugs were compared using retention times, capacity factors and relative capacity factors compared with an internal standard. The last method was found to give the most reproducible results. Considerable variations were found between the different brands of silica with a smaller variation between the batches of a single silica brand. However, unlike earlier studies, significant variations were found for separations on a single batch of silica which were partly attributed to differences in eluent preparation and column temperature.