A rapid, simple and sensitive colorimetric method for the simultaneous determination of chlorphenoxamine HCl and anhydrous caffeine was developed, based on charge-transfer complex formation of the drugs with rose bengal in basic media of pH 9.0. The chlorphenoxamine HCl (I) complex was measured at 588 nm whereas anhydrous caffeine (II) was measured at 551 nm. The optimal experimental parameters for colour production were studied. Beer's law was obeyed in the concentration ranges 2–40 and 2–34 g ml–1 for I and II, respectively. The Ringbom optimum concentration ranges were 3–36 and 3–30 g ml–1 for I and II, respectively. The results obtained showed good recoveries of 100.2 1.5 and 99.7 1.3% with relative standard deviations of 0.37 and 0.47% for I and II, respectively. Applications of the method to representative pharmaceutical dosage forms are presented and the validity assessed by applying the standard addition technique. |
