CATALYTIC SPECTROFLUOROMETRIC DETERMINATION OF ULTRATRACE MOLYBDENUM IN NATURAL FRESH-WATER

A highly sensitive fluorometric method was developed for the determina tion of molybdenum using the molybdenum-catalyzed oxidation of L-ascor bic acid with hydrogen peroxide and the successive condensation of deh ydroascorbic acid with o-phenylenediamine to produce fluorescent quino xaline derivatives. The fluorescence intensity (lambda(ex)=350 nm; lam bda(em)=425 nm) was proportional to the square of the reaction time (t ) in the initial reaction at pH 3.2 and 25 degrees C. Using the slope of the fluorescence intensity versus t(2) graph, a calibration graph f or molybdenum was constructed with a linear range of 0-3 mu gl(-1). Th e detection limit was 0.04 mu gl(-1) (0.2 ng). The addition of trans-1 ,2-cyclohexanediamine-N,N,N',N'-tetraacetic acid eliminated the interf erences from Cu(II), V(IV), V(V) and W(VI) of up to 50-100 mu gl(-1) a nd from Fe(II), Fe(III) and humic acid of up to 500-2000 mu gl(-1). Th e proposed method was successfully applied to analyses of river, lake and rain water samples.