Polyatomics in zinc isotope ratio analysis of plasma samples by inductively coupled plasma-mass spectrometry and applicability of nonextracted samples for zinc kinetics

Abstract

Inductively coupled plasma-mass spectrometry (ICP-MS) is a powerful tool for both quantitative multielement analyses of inorganic elements and measurement of isotope ratios (IRs). The main disadvantage of this technique is the existence of polyatomic isobaric interferences at some key masses. Zinc has been investigated for such potential interferences in serum or plasma. The Zn isotopes, 66Zn and 68Zn, have no apparent interferences, but 32S1602 and 32S2 are isobaric with 64Zn. The possible effects of S and other major components of blood plasma-Na, K, Cl, P, Ca-on Zn IRs were investigated using a series of mineral solutions which simulated human plasma with respect to these elements. The mixture of all mineral elements interfered only with 64Zn (6.66 ng/mL) and 70Zn (8.51 ng/mL). Interferences to 66Zn, 67Zn, and 68Zn were minimal containing 0.90, 0.94, and 0.39 ng/mL, respectively. The copresence of Na or S shifted 35Cl16O2 (atomic mass 67 coming from Cl solution) to 35Cl2 which reduced the contribution to 67Zn. The hypothesis that Zn IRs obtained from plasma at various intervals after the intravenous administration of enriched 67Zn to humans would reflect those obtained after extraction of Zn was therefore tested. To compare the two pretreatment methods, "extraction" versus "nonextraction," specimens were collected from 10 human subjects at intervals of 5 min to 24 h postinjection, and in 4 subjects from 5 min to 9 d postinjection. Two separate aliquots of plasma from each time-point were dried and digested with hydrogen peroxide, and the residue dissolved in nitric acid. One specimen was subjected to zinc extraction using ammonium diethyldithiocarbamate chelate followed by back extraction into nitric acid. The matching aliquot received no further pretreatment. The normalized IRs obtained from 67Zn/66Zn and 67Zn/68Zn in both the "extracted" and "nonextracted" samples agreed well (r2 = 0.976 and r2 = 0.985, respectively) compared to those from other ratios (r2 = 0.838 for 67Zn/64Zn and r2 = 0.747 for 67Zn/70Zn). Considering the minimum possibility of isobaric interferences in plasma samples, 67Zn/68Zn obtained from "nonextracted" samples is sufficient for routine Zn kinetic analysis by ICP-MS.

Zinc Binding in Pestivirus Npro Is Required for Interferon Regulatory Factor 3 Interaction and Degradation

“…Elemental, Cheshire, UK) using previously published protocols. 50,51 The nitric-acid-diluted samples were spiked with Yttrium ( 89 Y, 1 ng/mL) as an internal standard in order to correct the errors due to instrument drifts during data acquisitions. The amount of Zn was determined from the calibration curves for the normal zinc isotopes obtained by using the Zn standard at concentrations of 0, 5, 10, 25, and 50 ng/mL.…”

A stable‐isotope methodology for measurement of soil‐applied zinc‐fertilizer recovery in durum wheat (Triticum durum)

“…The determination of accurate 67/66 Zn ratios in samples can be complicated through the formation of isobaric and polyatomic interferences during ICP-MS analysis (Ramanujam et al, 1999). In this study, the most naturally abundant Zn isotope, 64 Zn, was not used to determine isotope ratios because of the potential interference of this isotope with nickel (e.g., 64 Ni), S (e.g., 32 S 16 O 2 ), and P (e.g., 31 P 16 O 2 H + ).…”

The use of ICPMS for stable isotope tracer studies in humans: a review

“…Spectral interferences are known to limit the applicability of quadrupole ICPMS for analysis of zinc isotopes [27,33] and elimination of these interferences either in the sample-preparation step or in the sample-introduction system is crucial. Nutritional studies designed to follow a zinc tracer in the body requires analysis of one or more of the sample matrices feces, urine, and blood/plasma samples [36,37,38,39].…”

“…The most commonly measured nutritional element using quadrupole ICPMS is zinc [22,23,24,25,26,27,28,29,30,31,32,33,34,35]. Spectral interferences are known to limit the applicability of quadrupole ICPMS for analysis of zinc isotopes [27,33] and elimination of these interferences either in the sample-preparation step or in the sample-introduction system is crucial.…”