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

A relatively simple and rapid method for the determination of trace amounts of molybdate in natural waters is proposed. Molybdate at mu g 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 Mo-99(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, Mo-101(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.