Abstract
Selenium(IV) and tellurium(IV) are quantitatively reduced and precipitated as metallic form in the N, N-dimethylformamide solution containing hydrochloric acid after heating on a water bath. Twenty to two hundred mg of selenium and tellurium can be determined gravimetrically by use of the reagents. Tartaric acid was used together with N, N-dimethylformamide to precipitate only selenium from mixtures of Se(IV) and Te(IV).
The recommended procedure is as follows: Take an aliquot of the sample solution containing Se(IV) (≤150 mg) and Te(IV)(≤100 mg) in a 100 ml beaker. Evaporate the solution up to dryness on a water bath after addition of nitric acid. Add 20 ml of hydrochloric acid and 50 ml of N, N-dimethylformamide, transfer the solution into a stoppered 200 ml Erlenmeyer-flask, and keep to stand for 4.5 hours in boiling water to complete the precipitation. Filter the precipitated selenium and tellurium on a sintered glass filter, and weigh the precipitate after washing and drying (weight A).
Then take the same volume of the sample solution in another beaker, treat as above, and then add(33.5)ml of hydrochloric acid (2+1) and 20 ml of N, N-dimethylformamide. Transfer the solution to a stoppered 100 ml Erlenmeyer-flask containing 2 g of tartaric acid, and heat for 3 hours in boiling water. Filter the precipitated selenium, and weigh selenium (weight B). The weight of tellurium is obtained as A-B. The effect of ten-odd cations and some anions on the determination was also examined.
