Spectrophotometric Determination of Bismuth(Ⅲ) in Drugs with Separation by Adsorption on Microcrystalline Thymolphthalein

It was found that micro-amounts of bismuth(Ⅲ) could be separated from K+, Na+, Ca2+, Mg2+, Zn2+, Fe3+, Co2+, Ni2+, Mn2+ and Al3+ by adsorption on microcrystalline thymolphthalein (added as 0.10 mL of 50 g·L-1 ethanol solution) in the form of an insoluble ternary ion association complex (DTMAB)3［BiI6］ through reaction in a mixture containing 0.80 mL of 0.10 mol·L-1 KI solution, and 0.30 mL of 1.0×10-2mol·L-1 dodecyltrimethylammonium bromide (DTMAB) solution, buffered to pH 3.0 with phthalate buffer solution, diluted to 10 mL, and thence added with 1.0 g of KBr. After shaking, 1.00 mL of the lower aqueous salt phase was taken and Bi(Ⅲ) in the solution was determined photometrically by the color reaction with 5-Br-PADAP in the presence of CTMAB. Absorbance of the color solution was measured at 555 nm. The proposed method was used for determination of bismuth in drug samples, giving results in consistency with the results found by EDTA titration. Values of RSD′s (n=6) found were ≤2.0%.