On the spectrophotometric determination of with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol

2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) is a suitable reagent for the spectrophotometric determination of uranium but results are easily influenced by the reaction conditions as well as various common ions and masking agents. Optimum conditions, which must be carefully maintained, are 30% (v/v) dimethylformamide, 0.1% triton X-100, ≥ 8 × 10−5 M 5-Br-PADAP, 8 × 10−2 M triethanolamine, 7 × 10−3 M sodium fluoride, 10−2 M 5-sulphosalicylic acid, and 579 nm. Sodium sulphate (10−2 M) and CDTA (5.7 × 10−3 M) may serve as additional masking agents. A previous separation of uranium by extraction with 0.1 M tri-n-octylamine in benzene from 4 M HCl and re-extraction of 0.3 M HCl is recommended for analysis of natural water samples.