Numerous chelating agents [l] have been used for the extraction and
spectrophotometric determination of vanadium(V). These reagents form 1: 2
(metabligand) complexes which have a basic V=O and an acidic V-OH
group in the same molecule. The V=O group reacts with acidic substances
(carboxylic acids, phenols) to give hyperchromic and bathochromic shifts
[2, 31. Cupferron (ammonium N-nitrosophenylhydroxylamine) reacts with
vanadium(V) to form a red 1:2 complex which can be extracted into chloroform
[4]. However, the extracted complex is unstable and decomposes
rapidly at room temperature. This has necessitated the presence of a stabilizer
and the use of lower temperatures for the determination of vanadium [ 51.
In this communication, vanadium(V) is extracted with cupferron in the
presence of phenols, to improve the stability of the complex and the sensitivity
and selectivity of the method. It was found that the V=O group reacts with
phenols to give a stable complex which provides the basis for a highly sensitive
extractive spectrophotometric determination. The reliability of the
method was checked by determining vanadium in standard steel samples