ULTRA TRACE ANALYSIS OF MOLYBDENUM BY DIFFERENTIAL PULSE POLAROGRAPHY AND ADSORPTIVE STRIPPING VOLTAMMETRY IN THE PRESENCE OF 2,5-DICHLORO-3,6-DIHYDROXY-1,4-BENZOQUINONE

Different polarographic and voltammetric techniques for the determination of molybdenum at the trace level have been investigated. As a result, a new high-sensitivity procedure for the determination of molybdenum by adsorptive stripping voltammetry was developed. The method is based on the reaction of molybdenum(VI) with 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid) to produce a complex which is absorbed onto mercury at -0.20 V (vs. Ag/AgCl, 3 mol/l KCl) from pH 2.7 solution. The cathodic stripping peak at -0.62 V can be used to determine molybdenum with a detection limit of 0.02 ng/ml after 5 min deposition time. The relative standard deviation for the determination of 0.1 ng/ml Mo after 5 min stirred collection was 6.6%. Interference from various inorganic ions and organic substances are reported. The method was applied to the determination of molybdenum traces in waters; interfering organic substances in polluted waters were destroyed by oxidative digestion in a microwave oven.