Physicochemical speciation of molybdenum in rain water

A combination of a sensitive catalytic determination method with filtration and ultrafiltration has been used for the physicochemical speciation of mo lybdenum in natural and synthetic rain water samples. The concentration (C- L) of labile molybdenum was evaluated by a direct catalytic determination. The total concentration (C-T) Of molybdenum was determined after the acid d ecomposition of the sample to calculate the non-labile concentration (C-T-C -L). From the speciation results, molybdenum species in the successive rain fall sample were found in a fraction with smaller molecular weights < 10(3) Da and characterized as labile forms, i.e. simple molybdate ions. Non-labi le molybdenum existed in particulate matter (greater than or equal to0.45 m um in particle size) and distributed predominantly in the initial rainfall sample. The coprecipitation with Fe(III) hydroxide contributed to the forma tion of the non-labile molybdenum. In the initial rainfall sample, a small part of molybdenum was labile in the particle fraction (greater than or equ al to0.45 mum). This type of molybdenum was associated with the formation o f humic iron aggregates. (C) 2001 Elsevier Science Ltd. All rights reserved .