Spectrophotometric determination of silver in lead and lead concentrates with thiocyanate and Rhodamine B

Abstract

The formation of a violet coloration when Rhodamine B is treated with silver in the presence of a large excess of thiocyanate is used for the spectrophotometric determination of silver. The colour is stabilised by adding poly(vinyl alcohol). At 600 nm the calibration graph is linear in the range 5–30 µg of silver per 25 ml of final solution with a relative standard deviation of 0.8% for 0.6 µg ml^–1 of silver. The molar absorptivity is 3.3 × 10⁴ l mol^–1 cm^–1. The sensitivity can be enhanced by recording the second-derivative spectrum and a sensitivity of 0.06 µg ml^–1 of silver can be achieved. The selectivity can be improved using the separation of silver with lead chloride as a collector. The method is applied to the determination of silver in metallic lead and lead concentrates.