Determination of five phenothiazines in pure and pharmaceutical preparations using vanadium pentoxide as a chromogenic reagent

Determination of two or more compounds in the same sample without previous chemical separation is a basic analytical problem. In the present study the resolution of the binary mixtures of compounds can be determined by a very simple, sensitive, and accurate spectrophotometric procedure. Five phenothiazine drugs namely, Promethazine HCl (PMH), Promethazine Theoclate (PMT), Chlorpromazine HCl (CPH), Trifluoperazine HCl (TFPH), Prochlorperazine Maleate (PCPM), in pure form and pharmaceutical formulations were assayed by a single chromogenic reagent (V2O5) in an acidic medium, to form a red colored complex having maximum absorbance range from 500 to 525 nm. The reaction is selective for these phenothiazine drugs with 0.05mg/10mL as visual limit of quantitation and thus provides a basis for a new spectrophotometric determination. The color reaction obeys Beer's Law from 0.05mg/10mL to 2mg/10mL for all five phenothiazines with a relative standard deviation from 0.63 to 0.80%. The quantitative assessments of tolerable amounts of other drugs were also studied. The results compare favorably with those of the official methods.