NON-EXTRACTIVE SPECTROPHOTOMETRIC DETERMINATION OF VANADIUM(V) IN ALLOYS AND ENVIRONMENTAL, BIOLOGICAL AND SOIL SAMPLES USING 5,7-DIBROMO-8-HYDROXYQUINOLINE

An ultra-sensitive and highly selective non-extractive spectrophotometric method is presented for the rapid determination of vanadium(v) at trace levels using 5,7-dibromo-8-hydroxyquinoline (DBHQ) as a new spectrophotometric reagent (lambda(max) = 400 nm) in slightly acidic solution (0.00015-0.016 mol(-1) sulfuric acid). The reaction is instantaneous and the absorbance remains stable for over 48 h. The average molar absorption coefficient and Sandell's sensitivity were found to be 6.1 x 10(3) l mol(-1) cm(-1) and 0.015 mu g cm(-2) of V-V, respectively. Linear calibration graphs were obtained for 0.1-20 mu g ml(-1) of V-V: the stoichiometric composition of the chelate is 1:3 (V:DBHQ). Large excesses of over 50 cations, anions and complexing agents (e.g., tartrate, oxalate, citrate, phosphate, thio-urea, SCN-) do not interfere in the determination. The method was successfully used in the determiantion of vanadium in several Standard Reference Materials (alloys and steels) as well as in some environmental waters (potable and polluted), biological samples (human blood and urine), soil samples and complex synthetic mixtures. The method has high precision and accuracy (s = +/- 0.01 for 0.5 mu g ml(-1)).