Rapid Colorimetric Determination of Selenium by the Tin (II)-Strong Phosphoric Acid Reduction Method

A new procedure for a rapid determination of selenium has been devised by the present authors. Tin(II)-strong phosphoric acid, previously prepared by the authors, has a remarkable decomposing and reducing power, and selenium in various forms can be reduced to hydrogen selenide which is evolved as a gas from samples. Sulfur in various forms is reduced to hydrogen sulfide at the same time. Solid samples such as pyrite can be allowed to decompose rapidly by simple heating with the reagent in an atmosphere of hydrogen. The gas evolved is introduced into an absorbing solution of 5 N sodium hydroxide. Then, a small volume of 30% hydrogen peroxide solution is added. Thus sodium selenate and sodium sulfate are formed in the solution. After adding an excess of concentrated hydrochloric acid and boiling for about twenty minutes with a reflux condenser, the selenic acid is reduced to selenious acid, while the sulfuric acid remains unchanged. The solution is kept at 45°C for several minutes, and solutions of gum arab...