The rapid colorimetric determination of molybdenum with dithiol in biological, geochemical and steel samples.

A rapid method for the determination of molybdenum in botanical, biological, geochemical and steel samples with dithiol, is described. Botanical and biological samples are ashed at 550 °C before leaching with 4 M hydrochloric acid, while geochemical samples are fused with potassium hydrogensulphate, and steels are decomposed with nitric and hydrochloric acids. The dithiol complex of molybdenum is formed by the addition of an alkaline solution of dithiol to the sample solution, and then extracted into isoamyl acetate. Ascorbic acid and citric acid are used to eliminate interferences from iron and tungsten, and the addition of potassium iodide gives the procedure very high tolerance to copper. Up to 150 geochemical samples or ashed botanical or biological samples can be analysed per man-day. Sensitivity of the method is 0.05, 0.5 and 10 p.p.m. for biological, geochemical and steel samples, respectively. The relative standard deviation is better than ±7% over the standard range used, and recovery of added molybdenum is complete.