Determination of microgram amounts of precious metals using X-ray fluorescence spectrometry

Microgram amounts of noble metals were localised with ammonium sulphide on filter absorbent pads and in cellulose pellets for spectrometer counting. The Kα1 lines of ruthenium, rhodium and palladium (tungsten tube) and the Lα1 lines of osmium, iridium, platinum and gold (molybdenum tube) were employed in conjunction with a lithium fluoride (200) analysing crystal. At the 95% confidence level, detection limits of 1.0 µg (ruthenium, rhodium and palladium) and 0.6 µg (osmium, iridium, platinum and gold) were observed for the pellet technique, with values of 0.6 and 0.2 µg, respectively, for the absorbent-pad method. The average coefficient of variation for the determination of 10 µg of the seven metals studied was 6.5% for both sample presentations. No inter-elemental matrix interferences were observed among the noble metals themselves. However, the presence of more than 200 µg of nickel or copper reduced the slopes of the calibration graph by a constant factor of 10% for the lighter metals, and amounts of more than 400 µg of the base metals reduced the slopes by 20% for the heavier members. Good agreement was found between the X-ray fluorescence procedures and standard atomic-absorption methods in analysis of ore concentrates.