EXTRACTION-SPECTROPHOTOMETRIC DETERMINATION OF CHROMIUM(VI) WITH HYDROXYAMIDINES

A new, simple, rapid, and selective spectrophotometric method for determining Cr(VI) by extraction with hydroxyamidines in chloroform over 0.2-0.8 M HCl is described. The molar extinction coefficient of the complexes of Cr(VI) with 10 different hydroxyamidines lie in the range of (1.30-1.52)X104 l mol-1cm-1 at λ(max) 390-400 nm. Of these, the simplest compound, N-hydroxy-N,N'-diphenylbenzamidine (HDPBA) has been chosen for the detailed studies. The limit for detection is 0.1 μg Cr/cm3. The composition of the complex, and the effect of solvents, acids and diverse ions on the extraction of the metal are discussed. The method is free from interference of most of the metal ions except Mn(VII) which is removed by reducing with sodium nitrite. The method has been applied for determination of chromium(VI) to water samples containing the metal at ppb levels.