The determination of 48Ca, 46Ca, and 44Ca by chemical and radiochemical neutron activation analysis

A chemical and radiochemical neutron activation analysis (CNAA/RNAA) method has been developed for the determination of three calcium isotopes (48Ca, 46Ca, and 44Ca) in a single sample derived from urine. This method was developed in support of clinical research using a dual enriched stable isotope methodology to study bone mineralization in premature infants, juvenile rheumatoid arthritics, and cystic fibrosis. In these studies, one enriched isotope of calcium is administered orally, 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 used to calculate true absorption of calcium. In our method, 48Ca is determined via the 48Ca(n,γ)49Ca reaction and 3084 keV gamma-ray, 46Ca via the 46Ca(n,γ)47Ca reaction and 1296 keV gamma-ray, and 44Ca via the 44CA(n,γ)45Ca reaction and 256 keV (max) beta-particle. A pair of chemical separation steps are employed to separate calcium 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 45Ca to remove interfering radionuclides. (author)