Flow injection manifold for the direct spectrophotometric determination of bismuth in pharmaceutical products using Methylthymol Blue as a chromogenic reagent

A new simple and rapid flow injection method is reported for the direct determination of bismuth in pharmaceutical products. Methylthymol Blue (MTB) was used as a chromogenic reagent and the absorbance of the colored Bi(iii)-MTB complex produced was monitored at 548 nm. The various chemical and physical variables were optimized and a study of interfering ions was also carried out. Linear calibration graphs were obtained from 0 to 100 mg l(-1) Bi(iii) (120 injections per hour). The precision was very good (s(r) = 1.3%) and the limit of detection was c(L) = 0.150 mg l(-1). The average accuracy was also very good (e(r) = 0.75%) and was evaluated by comparison of the results obtained with those claimed by the manufacturers. The method was found to be adequately selective, considering the ions that the samples contain.