Prof. Michael E. Ketterer, Department of Chemistry and Biochemistry, Northern Arizona University (NAU), Flagstaff, AZ and USTUR made a poster presentation at the 2008 Winter Conference on Plasma Spectrochemistry for Trace Element, Stable Isotope, and Elemental Speciation Analysis, Temecula, CA, January 7-12.
TP12 determination of U, Pu, and Am in biological samples by SF-ICPMS for biokinetic studies of actinides
Michael E. Ketterer (NAU), Sergei Y. Tolmachev (USTUR), Anthony C. James (USTUR), and Dorothy B. Stuit (USTUR)
Plutonium isotopes (239Pu, 240Pu, 241Pu), uranium isotopes (234U, 235U, 236U, and 238U), and 241Am were measured in digested bone and soft tissue samples with SF-ICPMS; these results were compared to results previously obtained by alpha spectrometry (AS). The samples were obtained from USTUR registrants (Cases 0269, 0425, 0720 and 1028) with known occupational exposure histories. Samples investigated in this study were obtained as un-spiked 6-8 M HCI solution aliquots from USTUR’s National Human Radiobiology Tissue Repository (NHRTR). USTUR dissolution procedures consist of dry-ashing, followed by complete decomposition of the residue with mineral acids and dissolution of the residue in aqueous HCI. Prior to ICPMS measurements, chemical separations were conducted using extraction chromatography. Sample extracts were 5-15 grams and typically represented only 1-3% of the total sample digest. 242Pu and 243Am were used as spike isotopes for the determination of Pu isotopes and 241Am, respectively. Pu was isolated using microcolumns of TEVA resin (EIChrom). Am was isolated using a three column sequence: TEVA-UTEVA-DGA. The TEVA and UTEVA were first used to remove Pu and U, respectively; thereafter, Am is retained and purified on a microcolumn comprised of DGA resin (EIChrom). Uranium activities were measured using two aliquots: an unspiked aliquot was used to prepare a U fraction with UTEVA resin; this unspiked aliquot was used to measure the 234U-235U-236U-238U isotopic composition. A second U aliquot was spiked with 236U and was used to measure U activities by comparison to standards prepared to known 236U/xxxU ratios. Since some of the samples contained 236U, two U runs per sample were required to subtract the indigenous 236U content. In future work, 233U of high isotopic purity will be used as a spike to measure all U isotope activities and ratios in a single sample aliquot.
The U, Pu, and Am results were compared to AS, which has long been used at USTUR for Pu and Am measurement after chemical separation of the analytes. Six bone and eight soft tissue samples were used and analyzed in the study. 239Pu and 240Pu activities, along with the 240Pu:239Pu atom ratio, were measured by ICPMS in 13 samples; 239+240Pu along with 238Pu were measured in all samples by AS. The 240Pu:239Pu atom ratios were uniform among individual cases (0.0628 ± 0.0022, 1 SD), and are consistent with 1950’s-1960’s weapons grade material. In one of the samples the 239+240Pu activity was below the SF-ICPMS detection limit. 238Pu measurements were not attempted by ICPMS due to isobaric interference from natural 238U. However, beta-emitting 241Pu was measured by SF-ICPMS in five samples of high 239+240Pu content. Positive correlation (r2 = 0.9997) was observed between 239+240Pu values measured by SF-ICPMS and AS. With SF-ICPMS, 241Am was measured in four samples out of five with high 239+240Pu. For a small number of data points (n =4) significant correlation (r2=9985) was observed between 241Am activities reported by SF-ICPMS and α-spectrometry. The comparison of SF-ICPMS with AS confirmed the suitability of the ICPMS method when applied to the analyses of 239+240Pu and 241Am in the USTUR samples. U measurements confirm the presence of grossly elevated U activities in soft tissues and bones of occupationally exposed individuals; some samples exhibited non-natural 238U:235U atom ratios and the presence of 236U, clearly indicating exposure to anthropogenic U.