Determination of Silver in Tungsten Ore and Molybdenum Ore by Inductively Coupled Plasma Mass Spectrometry with High Pressure Closed Digestion

As the current standard method of flame atomic absorption spectrometry in GB/T 14352.12—2010 was difficult to meet the detection requirements of low content silver, the study mentioned by the title was proposed. 0.100 0 g of tungsten or molybdenum ore sample was taken, and digested with 3 mL of hydrofluoric acid and 1 mL of nitric acid at 180 ℃ for 12 h in a sealed environment. After cooling, the solution was heated on a electric heating plate at 150 ℃ to remove the acid until white smoke was emitted, and then 1 mL of nitric acid was added. The mixture was evaporated to dryness, and 1 mL of nitric acid and 3 mL of water were added. The solution was heated in a sealed environment at 150 ℃ for 10 h. After cooling, the solution was transferred to a 100 mL-colorimetric tube, and made its volume up to 100 mL with 2% (volume fraction) nitric acid solution. Silver in the solution was determined by inductively coupled plasma mass spectrometry(ICP-MS) under the condition of kinetic energy discrimination collision mode, collision gas helium flow rate of 6.0 mL·min⁻¹, atomization gas flow rate of 0.85 L·min⁻¹, and radio frequency power of 1 550 W, and rhodium was selected as the internal standard for online calibration. As shown by the results, linear relationship between the mass concentration of silver and the corresponding signal intensity was found within 100.0 μg·L⁻¹, with detection limit (3s) of 0.008 μg·L⁻¹. This method was applied to the analysis of national first-class certified reference materials, and the determined values were basically consistent with the certified values, with RSDs of the determined values (n=12) in the range of 1.3%-3.8%. Test of recovery was made on the actual samples by the standard addition method, giving results in the range of 94.0%-105%.