Direct Microspectrophotometric Determination of Bismuth in Silver with Semi-Xylenol Orange

Abstract.

75–300 ng of bismuth in a sample mass of 20 mg of silver can be determined spectrophotometrically in a nitric acid medium (0.18 mol L⁻¹) with Semi-Xylenol Orange as chromogenic agent. Its selectivity is realized by using less toxic reagents in very small amounts to mask some of the interfering impurity cationic species while the matrix effect is negligible. The conditional formation constant of the colored chelate formed was found to be lg K′_f=3.1. It exhibits a maximum at 540 nm with a molar absorptivity of 4.2×10⁴ L mo1⁻¹ cm⁻¹. The linear regression equation for this determination is A=0.022+0.0018 C, where C stands for the concentration of Bi (ng per 0.5 mL) with a correlation coefficient γ of 0.9873. The RSD at the level of 200 ng of Bi (n=10) was found to be 5%.