Kinetic spectrophotometric determination of V(IV) in the presence of V(V) by the H-point standard addition method

The H-point standard addition method was applied to kinetic data for simultaneous determination of V(IV) and V(V) or selective determination of V(IV) in the presence of V(V). The method is based on the difference in the rate of complex formation between vanadium in two different oxidation states and xylenol orange at pH = 2. Vanadium(IV) can be determined in the range 0.2-5 mu g ml(-1) with satisfactory accuracy and precision in the presence of excess vanadium(V) and other metal ions that rapidly form complexes with xylenol orange under working conditions. The proposed method was successfully applied to the simultaneous determination of V(IV) and V(V) and also the selective determination of V(IV) in the presence of V(V) in several synthetic mixtures with different concentration ratios of V(IV) to V(V). (C) 2000 Elsevier Science B.V. All rights reserved.