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United States Department of Agriculture

Agricultural Research Service

Title: Ultra Low Dose 41ca: Testing the Detection Limits of Accelerator Mass Spectrometry-Based Analysis in Nutrition Research

item Hillegonds, Darren - CTR FOR ACCEL MASS SPEC
item Roughead, Zamzam
item Vogel, John - CTR FOR ACCEL MASS SPEC

Submitted to: Journal of Federation of American Societies for Experimental Biology
Publication Type: Abstract Only
Publication Acceptance Date: December 1, 2003
Publication Date: March 24, 2004
Citation: Hillegonds, D.J., Roughead, Z.K., Vogel, J.S. 2004. Ultra low dose 41ca: testing the detection limits of accelerator mass spectrometry-based analysis in nutrition research [abstract]. Federation of American Societies for Experimental Biology Journal. 18:A925.

Technical Abstract: Calcium radioisotopes, namely 45Ca and 47Ca, have provided useful insights into the metabolism of this essential nutrient. Until recently, it was not known that all 45Ca and 47Ca isotope preparations also contain 41Ca [1]. The amount of 41Ca present depends on the proportion of 40Ca in the enriched 44Ca or 46Ca target materials, the length of neutron activation, and the time between irradiation and use. 41Ca is considered an ideal tracer for longitudinal measurement of bone resorption because of its low natural abundance and long half life (105 y) which renders it radiologically benign. To determine the experimental detection limits for this isotope by accelerator mass spectrometry (AMS), archived urine samples were analyzed from 13 women who participated in a controlled feeding study in which daily calcium intake was constant. The subjects consumed labeled meals containing 4uCi of 47Ca, each containing 2pCi of 41Ca, 9 wk apart, and collected 48 h urine samples 1 and 3 wk after each set of labeled meals. Pooled samples from 2-3 persons yielded <25 umol CaF2. At wk 1, the 41Ca/Ca (weighted mean ± SD) was (4.3±1.1) x10-13, very close to the predicted value of 3x10-13. However, at wk 3, urinary 41Ca/Ca had subsided to near background levels. These findings help establish the lower limits of AMS methodology for both sample size (17-23 mL of urine) and 41Ca content (2 amol 41Ca or 0.082 fg). [1] Freeman et al., (2000) Nucl. Inst. Meth. Phys. Res. B, 172, 930-933.

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