CONTINUOUS DETERMINATION OF TRACE AMOUNTS OF HUMIC-ACID IN NATURAL-WATER BY CHEMILUMINESCENCE METHOD

A chemiluminescence (CL) method for the determination of humic acid (H A) based on the oxidation of HA with hydrogen peroxide in the presence of formaldehyde in alkaline solution is described. This method is sen sitive and selective for the determination of HA in natural water. HA produces strong CL in the oxidation of HA with MnO4-, Br2, ClO-, and C r2O72-, and the H2O2. HA-H2O2-HCHO system is suitable for the determin ation of HA because of its high sensitivity and high selectivity. The detection limit was 50 ppb and relative standard deviation for five me asurements of 0.5 ppm (w/w) HA was 1.8%. Cations such as Na+, K+, Mg2, Cu2+, and Fe3+ and anions such as PO43-, NO3-, CO32-, SO42-, Cl-, an d Y- (EDTA-Na) did not interfere with the determination of HA. Additio n of Mn(II) increased the CL intensity. The concentration of HA in nat ural water determined with this method is in good agreement with that determined by fluorometric analysis. (C) 1994 Academic Press, Inc.