Inductively Coupled Plasma Mass Spectrometric Analysis of Calcium Isotopes in Human Serum: A Low-Sample-Volume Acid-Equilibration Method

Abstract

Background: 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 L 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. Methods: Serum was collected from humans who were administered 42 Ca, and 20 L of serum was mixed with 2 mL of 0.22-0.67 mol/L HNO 3 at room temperature for between 1 min and 16 h. The 42 Ca/ 43 Ca 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. Results: 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 HNO 3 . Data obtained from these solutions were consistent with data from oxalate-precipitated calcium. The precision of 42 Ca/ 43 Ca ratio measurements was better than 0.5%.

Differential Effects of Paricalcitol and Calcitriol on Intestinal Calcium Absorption in Hemodialysis Patients

“…The control standard was analyzed 2–3 times between every 4–8 sample runs. Analytical precision was <0.5% relative standard deviation [24]. …”

Direct determination of selenium in human serum by inductively coupled plasma-collision cell-mass spectrometry

“…After 2 h, precipitation was observed in all solutions. Precipitation in human sera due to the addition of nitric acid is also described by Chen et al (9).…”

Calcium isotope analysis by mass spectrometry

“…Enriched stable isotopes are non‐toxic, and can be used for experiments in living organisms without any toxicological concern (Stürup, Hansen, & Gammelgaard, 2008). Because in vivo experiments are based on the determination of the calcium fraction absorbed in the body by measuring tracer concentrations in urine or serum, the majority of publications have dealt with those two types of samples (e.g., Stürup, Hansen, & Molgaard, 1997; Chen et al, 2003; Field et al, 2003; Simpson et al, 2005; Stürup, Bendahl, & Gammelgaard, 2006). Clinical and nutritional studies that involved calcium‐isotope tracers included assessment of mineral metabolism in children with acute or chronic diseases (Abrams, 2008), investigation of the effect of vitamin D on calcium absorption by human organism (Lee et al, 2002), and comparative studies of internal absorption of Ca from selected foodstuffs and from pharmaceutical preparations (Werner et al, 1999).…”