Winter Conference on Plasma Spectrochemistry, Temecula, CA, January 7-12, 2008

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. [USTUR-0238-08]

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