Determination of Rare Earth Elements in Petroleum by ICP-MS

The decomposition of a sample by the high pressure oxygen combustion method and the preconcentration process using chelating resin (Chelex 100) were studied for the determination of rare earth elements (REEs) in petroleum by ICP-MS. In the decomposition procedure, a I g of petroleum sample was burnt in 3 MPa of Oxygen in a stainless vessel with 5 ml of 5% HNO3 - 1% H2O2 absorbing solution. In the preconcentration process, the pH of absorbing solution after the combustion was adjusted at 4 with an ammonia solution and then stirred after the addition of I g of chelating resin (Chelex 100). The resin was collected on a glass filter. REEs ions adsorbed on the resin were eluted with 2 mol/l HNO3. The solution was transferred to 10 ml volumetric flask and REEs were measured by ICP-MS with internal standard elements, such as Be for Sc, In for Y similar to Sm and Re for Eu similar to Lu. The observed concentration of REEs were corrected by subtracting the spectral interferences. REEs in some real petroleum samples were determined.