title: High-precision measurement of variations in calcium isotope ratios in urine by multiple collector inductively coupled plasma mass spectrometry.
abstract: We describe a new chemical separation method to isolate Ca from other matrix elements in biological samples, developed with the long-term goal of making high-precision measurement of natural stable Ca isotope variations a clinically applicable tool to assess bone mineral balance. A new two-column procedure utilizing HBr achieves the purity required to accurately and precisely measure two Ca isotope ratios ((44)Ca/(42)Ca and (44)Ca/(43)Ca) on a Neptune multiple collector inductively coupled plasma mass spectrometer (MC-ICPMS) in urine. Purification requirements for Sr, Ti, and K (Ca/Sr > 10 000; Ca/Ti > 10 000 000; and Ca/K > 10) were determined by addition of these elements to Ca standards of known isotopic composition. Accuracy was determined by (1) comparing Ca isotope results for samples and standards to published data obtained using thermal ionization mass spectrometry (TIMS), (2) adding a Ca standard of known isotopic composition to a urine sample purified of Ca, and (3) analyzing mixtures of urine samples and standards in varying proportions. The accuracy and precision of δ(44/42)Ca measurements of purified samples containing 25 μg of Ca can be determined with typical errors less than ±0.2‰ (2σ).
authors: Arizona State University, Department of Chemistry and Biochemistry, Tempe, Arizona 85287, United States. jenniferllmorgan@gmail.com
authors: Jennifer L L
authors: JL
authors: Morgan
authors: Gwyneth W
authors: GW
authors: Gordon
authors: Ruth C
authors: RC
authors: Arrua
authors: Joseph L
authors: JL
authors: Skulan
authors: Ariel D
authors: AD
authors: Anbar
authors: Thomas D
authors: TD
authors: Bullen
mesh_terms: D015519:Bone Density; D002118:Calcium / Q000302:isolation & purification / Q000652:urine*; D002127:Calcium Isotopes / Q000652:urine; D002852:Chromatography, Ion Exchange / Q000379:methods; D006801:Humans; D018054:Hydrobromic Acid / Q000737:chemistry; D013058:Mass Spectrometry / Q000379:methods*
chemical_list: D002127:Calcium Isotopes; D018054:Hydrobromic Acid; D002118:Calcium