Rapid determination of molybdate in natural waters by coprecipitation and neutron activation analysis

Abstract

A relatively simple and rapid method for the determination of trace amounts of molybdate in natural waters is proposed. Molybdate at µg L^–1 levels in water samples could be measured through the combination of the proposed coprecipitation method and neutron activation analysis. Quantitative coprecipitation of molybdate was performed by the use of thionalide–ammonium pyrrolidinedithiocarbamate as coprecipitation reagent at pH 1.2. The coprecipitation system was investigated with the use of ⁹⁹Mo(t_1/2 = 66.2 h) as radiotracer. The precipitate was collected on a membrane filter for neutron activation analysis. In order to reduce the working time, ¹⁰¹Mo(t_1/2 = 14.6 min) was used for the quantification after neutron activation. The irradiation and waiting time is almost 100-fold shorter by employing this alternative measurement system. The detection limit of molybdate was found to be about 1 ng L^–1. The method was validated by the analysis of certified reference materials (NASS-2 and SLRS-1) and it can be satisfactorily applied to the determination of trace amounts of molybdate in various aqueous systems.