Abstract
A method is described for the measurement of calcium isotopic ratios ( 42 Ca + : 43 Ca + and 44 Ca + : 43 Ca + ) 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 44 Ca + : 43 Ca + and 42 Ca + : 43 Ca + , respectively. Using a mass spectrometric resolution setting of 4000, the calcium peaks were resolved from interfering polyatomic ions ( 40 Ar 2 H + and 40 ArH 2 + on 42 Ca + and 28 Si 16 O + and 12 C 16 O 2 + on 44 Ca + ). Interferences from Sr 2+ , which cannot be resolved even using high resolution, were corrected for mathematically using the 43.5 Sr 2+ peak. The sample preparation step consisted of a simple 50-fold dilution of the urine sample with 0.14 M HNO 3 , which ensured a relatively high sample throughput of 6 samples per hour.
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