Determination of natural uranium and thorium in environmental samples by ETV-ICP-MS after matrix removal by on-line solid phase extraction

An on-line solid phase extraction method has been developed for the determi nation of U-238 and Th-232 biological certified reference material using in ductively coupled plasma mass spectrometry (ICP-MS). Absolute detection lim its were 2.7 pg and 3.1 pg for the determination of U-238 and Th-232 respec tively, both being blank limited. The result for the determination of U-238 in NASS-4 Open Ocean Sea water was 2.13 +/- 0.28 ng ml(-1) compared with a certified value of 2.68 +/- 0.12 ng ml(-1). The results for the determinat ion of U-238 in SLRS-3 River Water was 0.043 +/- 0.002 ng ml(-1) compared w ith an indicative value of 0.045 ng ml(-1). Results for the determination o f U-238 and Th-232 in NIST 1575 Pine Needles were 14.6 +/- 3.4 ng g(-1) and 28.3 +/- 4.5 ng g(-1) respectively compared with certified values of 20 +/ - 3 ng g(-1) and 37 +/- 3 ng g(-1), using a dry and wet ashing sample prepa ration method. Results for the determination of U-238 and Th-232 in NIST 15 66a oyster tissue were 121 +/- 21 ng g(-1) and 29 +/- 8 ng g(-1) for U-238 and Th-232 compared to certified and indicative values of 132 +/- 12 ng g(- 1) and 40 ng g(-1), using the same method. When a lithium metaborate fusion method was used, results for U-238 and 232Th Were 23.3 +/- 2.0 ng g(-1) an d 36.2 +/- 5.6 ng g(-1) respectively in NIST 1575 Pine Needles. The applica tion of electrothermal vaporisation ICP-MS (ETV-ICP-MS) to NASS-4 Open Ocea n Sea Water gave 2.81 +/- 0.54 ng ml(-1) and SLRS-3 River Water 0.045 +/- 0 .003 ng ml(-1) for U-238. When the fused NIST 1575 samples were analysed us ing ETV-ICP-MS, results for U-238 and Th-232 were 19.5 +/- 1.7 ng g(-1) and 38.8 +/- 2.2 ng g(-1) respectively. Absolute detection limits for ETV-ICP- MS were 30 fg and 9 fg for U-238 and Th-232 respectively, both being blank limited.