Abstract:Trace elements iron, copper, lead, tin, arsenic, silver, chromium, nickel and vanadium in oil sample were determined by inductively coupled plasma mass spectrometry (ICP-MS). The oil sample in the crucible was sub-boiling distilled in a muffle furnace until organic materials completely were evaporated. At 500 ℃ the residue was burned to form ashes. The ashes were soaked in the mixture of nitric acid and hydrogen peroxide, and dissolution was completed on heating plates. The sample solution was heated to boiling point in order to decompose hydrogen peroxide. Above sample treatment completely eliminated the interference of organic matter on mass spectrometry measurement. Additionally, after the sample treatment composition of the testing solution became simple and the matrix effects were reduced. Internal standard correction was not necessary but instead, the sample could be determined directly by the calibration curve of a pure solution. Optimization of the type and amount of digestion reagents, isotope usage and working conditions of equipment were completed in order to eliminate spectral interferences and blank background effect. The super trace impurities in high-voltage transformer insulating oil were determined and the results showed that: the recovery: 91% ~110 %, relative standard deviation(RSD) <3%, detection limit: 0.0059～0.0099 μg/L, BEC: 0.0003～0.0012μg/L.