Simple trace determination of platinum in geological materials

A direct, sensitive and simple method for the determination of sub-microgram amounts of platinum in acid leachates from geological materials is described. The sample is sized to plus 80-mesh and roasted at 700°C. During this operation the most important interfering elements such as C, S, Hg, Se, Te and As are eliminated. Anions and small amounts of most cations found in strongly acid leachates from rock samples do not interfere. Hydrogen peroxide is used as the oxidant during leaching with 5–7 M HCI. Platinum is reacted with Sn²⁺ after filtration. Addition of Rhodamine 6G precipitates a red quaternary complex. The colloidal suspension is suitable for spectrophotometric determination of platinum. While the reagent absorbance at 530 nm decreases, a peak due to the colloid appears at 565 nm. Beer's law is obeyed up to 0.6 absorbance unit, which corresponds to about 1.7 μg/ml of Pt. The sensitivity (3 times the noise level) corresponds to 0.01 μg/ml of Pt. A test procedure is described for serial analysis of 1–3-g powdered samples which enables an operator to perform from 30 to 50 analyses per man-day in the concentration range of 0.1–17 ppm of platinum. The procedure has been validated against standard samples and a recovery of 90% has been obtained with unspiked samples.