CATALYTIC SPECTROPHOTOMETRIC DETERMINATION OF PICOGRAM AMOUNTS OF VANADIUM IN NATURAL FRESH AND TAP WATER BY FLOW-INJECTION ANALYSIS

A highly sensitive spectrophotometric FIA method is proposed for the d etermination of vanadium using the vanadium catalyzed oxidation of o-p henylenediamine with bromate at pH 4.0 and 50 degrees C in the presenc e of gallic acid as an activator. The same calibration graph with a li near range of 0 - 8 mu g l(-1) was obtained for V(IV) and V(V) by the proposed method. The detection limit and typical sampling frequency we re 4 ng l(-1) (0.8 pg) and 30 samples h(-1), respectively. Iron ions o f up to 5 mu g l(-1) and humic acid of up to 3000 mu g l(-1) were tole rable in the determination of 0.2 mu g l(-1) of vanadium; the latter v alue was markedly improved compared to that with a manual-batch fluoro metric method. The proposed method was successfully applied to analyse s of lake, river, ground, rain and tap water samples containing vanadi um down to 0.02 mu g l(-1).