DETERMINATION OF SUBMICROGRAM LEVELS OF MOLYBDENUM IN ENVIRONMENTAL SAMPLES BY PULSE POLAROGRAPHY

ABSTRACT Study of environmental contamination (air, water, atmospheric fallout, by molybdenum trioxide in the vicinity of steelworks requirs a very sensitive method to be set up because flame atomic absorption and spectrophotometric procedures were not found sensitive enough. The improved method of determination use a pulse polarography procedure based upon the catalytic reduction of NO 3 - by Mo(III) formed by electrochemical reduction of Mo(VI) in 0.2 M H 2 SO 4 medium. The electrochemical signal obtained for a molybdenum concentration of 5.10 -8 M is not affected by Fe(III) at a concentration of 10 -3 M by Mn(II), Cu(II), Pb(II), Cd(II), Zn(II) at 10 -4 M. The main interference is caused by Sb(III) and Cu(II) but only in the presence of Cl - . The interference is elimined by previous treatment of the sample with K MnO 4 . In these conditions levels of molybdenum as low as 1 × 10 -8 M can be determined directly. Determination of the Mo content of sedimentable particles is made after perchloric solubilisation of the sample. This method is more sensitive and accurate than the thiocyanate spectrophotometric method used for the determination of submicrogram levels of molybdenum in environmental samples.