Spectrophotometric determination of bismuth(Ⅱ) after separation by coprecipitation of its 2-mercaptobenzothiazole complex with naphthalene

A method is described for the spectrophotometric determination of trace amounts of bismuth(Ⅱ) after separation by coprecipitation of its 2-mercaptobenzothiazole complex with naphthalene. 2-mercaptobenzothiazole reacts with bismuth(Ⅱ) to form a water-insoluble complex, which is easily coprecipitated with micro-crystalline naphthalene and the resulting mixture of the complex and naphthalene is dissolved in DMF. The absorbance of the solution is measured at 394 nm to determine the trace amounts of bismuth(Ⅱ). The various factors such as pH, amounts of reagent and naphthalene, shaking time, standing time and diverse ions are studied