Submitted to: Journal of Analytical Atomic Spectrometry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/1999
Publication Date: N/A
Interpretive Summary: The absorption of calcium by human subjects can be measured by using two special forms of natural calcium (stable isotopes). One form is injected while the other is consumed orally. The relative amounts of the two isotopes of calcium in urine, blood serum and, for lactating women, breast milk can be used to determine absorption. Measuring the amounts of these calcium isotopes in the past has required expensive equipment that is not widely available. This manuscript describes the use of a more widely available instrument, a quadrupole inductively coupled mass spectrometer, operated in a low power mode, to measure several isotopes of calcium. The utility of the method was demonstrated by analyzing samples from a study of calcium absorption by lactating women. Calcium absorption values calculated from urine, blood serum, and breast milk samples were nearly equivalent regardless of the type of sample. The described method should benefit human metabolic studies of calcium by demonstrating that widely available equipment can be used for calcium stable isotope measurements.
Technical Abstract: A method for the measurement of calcium isotopes (42Ca, 43Ca and 44Ca) using quadrupole inductively coupled plasma mass spectrometry (ICP-MS) is described. Interferences from polyatomic ions such as 12C60O2+ and 40ArH2+ at the calcium masses are greatly minimized by operating the ICP-MS in the cool plasma mode. Relative standard deviations (RSD) for the 42Ca:43Ca and d44Ca.43Ca ratios were found to be about 0.25%. Sample preparation involve using ammonium oxalate at a pH of 8 to separate calcium from samples such as serum, urine, feces and breast milk. The isotope ratio measurements are used to determine fractional absorption of calcium by a lactating women after intravenous administration of 42Ca and ingestion of 44Ca.