The polarographic determination of selenium in urine.

Polarographicdata are presented for the reduction of selenite ion in 3M sulfuric acid, 1M potassium chloride, and 1M ammonia-ammonium chloride. In these first two media two waves are obtained correspondingto the diffusion-controlled reduction of selenite ion to selenium amalgam and the adsorption of selenite ion on the mercury drop, respectively. One wave is obtained in ammonia-ammonium chloride correspondingto the reduction of selenite to selenide ion. Selenium has been determined in urine over a concentration range of 0.0063 to 0.175 mM. (0.5 to 14 sg./mi., in a 10-mi. sample) with an average error of 2 per cent. The effects of the time and method of storage on the lossof selenium by urine have been investigated. Although selenium is lost by urine under all methods investigated, storage in a deep freeze results in greater sample stability. It was also found that this loss could be prevented if the urine was made 1 molar to nitric acid.