Spectrophotometric Determination of Sibutramine Hydrochloride with Bromophenol Blue as Color Reagent

In a B-R buffer solution of pH 3.70, an ionic association complex, with molar ratio of 1 to 2 was formed by the reaction of sibutramine hydrochloride with bromophenol blue, having the positive absorption maxmum at the wavelength of 436 nm and negative absorption maximum at 590 nm. Ranges of linearity found at the 2 absorption maxima were within 3.4×10-6mol·L-1 and 3.8×10-6mol·L-1, with their values of apparent molar absorptivity of 1.83×105L· mol-1·cm-1 and 5.51×104L·mol-1·cm-1 respectively. Based on these facts, a method of spectrophotometric determination of sibutramine hydrochloride was proposed. The present method was applied to the determination of sibutramine hydrochloride in simulated samples and urine samples, giving values of recovery and RSD′s (n=6) in the ranges of 96.8%-102.5% and 0.9%-1.7% respectively.