Spectrophotometric determination of tungstate using an iron salt, a thiol and oxygen

Abstract

A simple, fast and inexpensive method for the determination of tungstate has been developed. The determination uses only reagents that are commonly found in biochemistry laboratories, i.e., iron(II) ammonium sulphate or iron(III) chloride, a thiol such as cysteine, 2-aminoethanethiol or 2-thioethanol, oxygen gas and a buffer (phthalate, acetate or glutarate) at pH 5.8. A compound of unknown structure is formed, which has an absorbance maximum at 475 nm (for cysteine) with ε= 420 l mol^–1 cm^–1, allowing the determination of 0.5–10 µmol of tungstate in a volume of 1 ml.