Measurements of Ca-44:Ca-43 and Ca-42:Ca-43 isotopic ratios in urine using high resolution inductively coupled plasma mass spectrometry

A method is described for the measurement of calcium isotopic ratios (Ca-42(+):Ca-43(+) and Ca-44(+):Ca-43(+)) in human urine using high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS), Relative standard deviations (RSD) of 0.33 and 0.41% were found for Ca-44(+):Ca-43(+) and Ca-42(+):Ca-43(+), respectively, Using a mass spectrometric resolution setting of 4000, the calcium peaks were resolved from interfering polyatomic ions ((ArH+)-Ar-40-H-2 and (ArH2+)-Ar-40 on Ca-42(+) and (SiO+)-Si-28-O-16 and (CO2+)-C-12-O-16 on Ca-44(+)), Interferences from Sr2+, which cannot be resolved even using high resolution, were corrected for mathematically using the Sr-43.5(2+) peak, The sample preparation step consisted of a simple 50-fold dilution of the urine sample with 0.14 M HNO3, which ensured a relatively high sample throughput of 6 samples per hour.