Uranium and thorium isotopic determination in environmental samples by Id-FI-ICP-MS

Direct uranium isotopic determination by ICP-MS on sweeps samples have been successful tested on inter-laboratory exercises carried out by the US-DOE. However, to determine uranium (238U, 235U and 234U) and thorium (232Th and 230Th) isotopic composition in environmental samples it is necessary to include analytical steps aiming the matrix separation and the pre-concentration of these radionuclides. On the other hand, there is a need to reduce the manpower involved on our laboratories. Therefore, the use of the flow injection technique coupled to a quadrupole ICP-MS was investigated due its potential further automation, 229Th and 233U were applied as isotopic tracers. UTEVA (Eichrom Technologies Inc.) cartridges were applied as a tool for uranium and thorium concentration and matrix separation. About 10 mL sample solution (3 M HNO3) is pumped through the cartridge, follows a washing step, also with 3 M HNO3, and uranium and thorium are eluted together using a 0.05 M ammonium oxalate solution. Based on uranium standard solution (10 ng L-1), the precision achieved is better than 3%. (author)