THE DETERMINATION OF CA-48, CA-46, AND CA-44 BY CHEMICAL AND RADIOCHEMICAL NEUTRON-ACTIVATION ANALYSIS

A chemical and radiochemical neutron activation analysis (CNAA/RNAA) m ethod has been developed for the determination of three calcium isotop es (Ca-48, Ca-46, and Ca-44) in a single sample derived from urine. Th is method was developed in support of clinical research using a dual e nriched stable isotope methodology to study bone mineralization in pre mature infants, juvenile rheumatoid arthritics, and cystic fibrosis. I n these studies, one enriched isotope of calcium is administered orall y, and one is administered intravenously. By making determinations of three isotopes (two enriched, one unenriched) within the same sample, the perturbation from natural isotopic ratios can be determined and us ed to calculate true absorption of calcium. In our method, Ca-48 is de termined via the Ca-48(n,gamma)Ca-49 reaction and 3084 keV gamma-my, C a-46 via the Ca-46(n,gamma)Ca-47 reaction and 1296 keV gamma-ray, and Ca-44 via the Ca-44(n,gamma)Ca-45 reaction and 256 keV (max) beta-part icle. A pair of chemical separation steps are employed to separate cal cium from urine as calcium oxalate with a yield in the range of 80-90% , and a radiochemical step is employed prior to the measurement of Ca- 45 to remove interfering radionuclides.