Abstract
A simple and sensitive method for the individual and simultaneous determination of ephedrine (EP) and phenylephrine(PE) has been developed. The individual method is based on direct measuring the absorbance of the resulting reddish colour at 526 and 545 nm for EP and PE, respectively. The simultaneous determination is based on measuring the absorbance at isodeferential point of 545 and 526 nm in the first order derivative spectra for EP and PE. The calibration graphs in the direct measurements were found to be linear over the range of 5 - 40 and 2 - 50 mu g/ml for EP and PE, with lower detection limit of 1.5 and 0.5 ppm, respectively. The molar absorptivity was calculated to be 0.2 x 10(4) and 0.6 x 10(4) l. mol(-1) cm(-1) with Sandell's sensitivity being 0.098 and 0.0276 mu g/cm(2), respectively. While the calibration graphs in the first order derivative (simultaneous) were found to be linear in the range of 10 - 40 and 5 - 50 mu g/ml, respectively. The relative standard deviation for five replicate analyses of 10 mu g/ml EP and PE were 1.3 and 1.15% respectively. The proposed method has been successfully applied for the determination of EP and PE in pharmaceutical formulation and in synthetic mixtures.