The determination of⁴⁸Ca,⁴⁶Ca, and⁴⁴Ca by chemical and radiochemical neutron activation analysis

Abstract

A chemical and radiochemical neutron activation analysis (CNAA/RNAA) method has been developed for the determination of three calcium isotopes (⁴⁸Ca,⁴⁶Ca, and⁴⁴Ca) 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 the⁴⁸Ca(n,γ)⁴⁹Ca reaction and 3084 keV gamma-ray,⁴⁶Ca via the⁴⁶Ca(n,γ)⁴⁷Ca reaction and 1296 keV gamma-ray, and⁴⁴Ca via the⁴⁴Ca(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 of⁴⁵Ca to remove interfering radionuclides.