Abstract

Inductively Coupled Plasma Dynamic Reaction Cell Quadrupole Mass Spectrometry (ICP-DRC-QMS) was characterized for the detection of the six naturally occurring calcium isotopes. The effect of the operating conditions of the DRC system was studied to get the best signal-to-noise ratio. This experiment shows that the potentially interfering ions such as <TEX>$Ar^+$</TEX>, <TEX>${CO_2}^+$</TEX>, <TEX>${NO_2}^+$</TEX>, <TEX>$CNO^+$</TEX> at the calcium masses m/z 40, 42, 43, 44 and 48 were removed by flowing <TEX>$NH_3$</TEX> gas at the rate of 0.7 mL/min <TEX>$NH_3$</TEX> as reactive cell gas in the DRC with a RPq value (rejection parameter) of 0.6. The limits of detection for <TEX>$^{40}Ca$</TEX>, <TEX>$^{42}Ca$</TEX>, <TEX>$^{43}Ca$</TEX>, <TEX>$^{44}Ca$</TEX>, and <TEX>$^{48}Ca$</TEX> were 1, 29, 169, 34, and 15 pg/mL, respectively. This method was applied to the determination of calcium in synthetic food digest samples (CCQM-P13) provided by LGC for international comparison. The isotope dilution method was used for the determination of calcium in the samples. The uncertainty evaluation was performed according to the ISO/GUM and EURACHEM guidelines. The determined mean concentration and its expanded uncertainty of calcium was (<TEX>$66.4{\pm}1.2$</TEX>) mg/kg. In order to assess our method, two reference samples, Riverine Water reference sample (NRCC SLRS-3) and Trace Elements in Water reference sample (NIST SRM 1643d), were analyzed.