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ARS Home » Plains Area » Houston, Texas » Children's Nutrition Research Center » Research » Publications at this Location » Publication #175850
Title: INDUCTIVELY COUPLED PLASMA MASS SPECTROMETRIC ANALYSIS OF CALCIUM ISOTOPES IN HUMAN SERUM: A LOW-SAMPLE-VOLUME ACID-EQUILIBRATION METHOD

Author
item CHEN, ZHENSHENG - BAYLOR COLLEGE OF MED
item Griffin, Ian
item KRISEMAN, YANA - BAYLOR COLLEGE OF MED
item LIANG, LILY - BAYLOR COLLEGE OF MED
item Abrams, Steven

Submitted to: Clinical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2003
Publication Date: 9/19/2003
Citation: Chen, Z., Griffin, I., Kriseman, Y.L., Liang, L.K., Abrams, S.A. 2003. Inductively coupled plasma mass spectrometric analysis of calcium isotopes in human serum: a low-sample-volume acid-equilibration method. Clinical Chemistry. 49(12):2050-2055.

Interpretive Summary: Stable isotopes are safe, naturally occurring, non-radioactive forms of elements that are widely used for studying metabolism in humans. For studies of calcium metabolism major limiting factors in the more widespread use of stable isotopes were the large amount of blood needed to make measurements, and the expense of the equipment needed for analysis. This was particularly true of kinetic studies were a large number of blood and urine samples were needed. In this paper we describe a new method of measuring calcium stable isotope ratios from blood and urine samples. We use an acid extraction method to purify samples, and measured isotope ratios using an induction coupled plasma mass spectrometer, which can run samples much more quickly (and cheaper) that the thermal ionization mass spectrometer used previously. This new method has several major advantages (1) it uses much small samples that normal, (2) samples are run much more quickly, and (3) costs are reduced. Although the results are not quiet as precise as using a thermal ionization mass spectrometer, the advantages in cost and time terms means that many samples can now be run using the induction coupled plasma mass spectrometer rather than the thermal ionization mass spectrometer.

Technical Abstract: Analytical methods for measuring the calcium isotope distribution in enriched human serum samples that use low blood volumes, simple preparation methods, and rapid analysis are important in clinical studies of calcium kinetics. Previously, sample preparation by oxalate precipitation typically required 500 µL of serum. This method was time-consuming, and the blood volume required was limiting in circumstances when only a small amount of serum could be obtained. Serum was collected from humans who were administered 42Ca, and 20 µL of serum was mixed with 2 mL of 0.22-0.67 mol/L HNO3 at room temperature for between 1 min and 16 h. The 42Ca/43Ca ratio in the supernatant was measured by a magnetic sector inductively coupled plasma mass spectrometer (ICP-MS). Calcium isotope ratios from these equilibration solutions were compared with data from oxalate-precipitated serum samples to determine the optimum equilibrium time and the effect of acid concentration on equilibrium. Various amounts of aggregated particles developed in different acid-serum mixtures. These affected the time required for isotope equilibration in the mixture. The shortest equilibrium time needed for the calcium isotopes varied from 1 to 6 h for samples acidified with 0.22-0.45 mol/L HNO3. Data obtained from these solutions were consistent with data from oxalate-precipitated calcium. The precision of 42Ca/43Ca ratio measurements was better than 0.5%. We have developed a simple, rapid sample preparation technique for ICP-MS analysis in which 20 µL of serum can be used for accurate measurement of the calcium isotope distribution in a sample with good precision and a rapid analysis time.