Development of a standardized analysis strategy for basic drugs, using ion-pair extraction and high-performance liquid chromatography - III. Analysis of pharmaceutical dosage forms.

The usefulness of the standardized analysis strategy previously described for the determination of basic drugs in pharmaceutical dosage forms is evaluated. Several examples which typify experience in applying the strategy are reported. Ion-pair extraction techniques are compared with each other and with a classical extraction method in terms of their efficiency. The extraction technique with di(2-ethylhexyl)-phosphoric acid (HDEHP) is found to be the method of choice. The use of an internal standard is recommended. The selection of a suitable compound is greatly facilitated by referring to the chromatographic properties. It is shown that it is not necessary for the analyte and internal standard to be structurally similar. The combination of the HDEHP extraction technique with the preferred HPLC systems has been shown to be very useful in the routine analysis of pharmaceutical dosage forms.