In this study, the effect of change in chromatographic process variables on the retention behavior of four drugs employed in erectile dysfunction therapy on a calixarene stationary phase is described. Three of these drugs are known to treat erectile dysfunction, namely, sildenafil citrate, tadalafil, and apomorphine hydrochloride, and one drug that is used as opioid analgesic, tramadol hydrochloride, which is quiet widely misused to treat premature ejaculation. The results indicate the importance of considering the structure and pK(a) values of drugs to be separated along with mobile phase composition. A new optimized, rapid, and accurate liquid chromatography method is also established for simultaneous determination of sildenafil citrate, tadalafil, and apomorphine hydrochloride in pharmaceutical preparations and bulk powders. The chromatographic separation of the three pharmaceuticals was achieved on a calixarene column in less than 10 min using a binary mobile phase of 35% acetonitrile and 65% 50 mM sodium perchlorate pH2.5 at 1 mL/min flow rate. The method was validated for system efficiency, linearity, accuracy, precision, limits of detection and quantitation, specificity, stability, and robustness. Statistical analysis proved that the method enabled reproducible and selective quantification of all three analytes in bulk drugs and in pharmaceutical preparations.
