title: Extraction of serum and urine calcium with ion exchange membrane filters for isotope enrichment determination using thermal ionization mass spectrometry.
abstract: The extraction of calcium from water, serum, and urine using Bio-Rex 25 mm ion exchange membrane filters was compared with the oxalate precipitation procedure currently used in our laboratory. Total recoveries of a known quantity of calcium loaded onto the membrane filters for water, serum and urine were as follows: (a) cation exchange filter, 85%, 74%, and 66%; (b) Chelex, 65%, 98%, and 20%; and (c) oxalate precipitation, 93%, 100%, and 96%, respectively. Regression analysis for precipitation versus ion exchange isotope ratio measurements of standards prepared using highly enriched calcium-44 showed slopes of unity. An improvement of automated sample analysis was observed for water and urine calcium samples extracted with ion exchange filters.
authors.affiliation: Laboratory of Theoretical and Physical Biology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: N E
authors.initials: NE
authors.lastname: Vieira
authors.forename: A L
authors.initials: AL
authors.lastname: Yergey
mesh_terms: D002118:Calcium / Q000032:analysis* / Q000097:blood / Q000652:urine; D002127:Calcium Isotopes; D005374:Filtration; D006801:Humans; D013058:Mass Spectrometry
chemical_list: D002127:Calcium Isotopes; D002118:Calcium