Abstract
A method has been described for the determination of iron from fish otoliths containing high levels of calcium by collision cell technology (CCT) ICP‐MS. Iron (Fe) in otolith solutions was quantitatively coprecipitated with small amounts of calcium hydroxide by adding 1.0 M sodium hydroxide solution. The performance of CCT‐ICP‐MS pressurized with He/H~2~ cell gas was investigated on the elimination of Ca‐based spectral interferences at m/z 54, 56 and 57. Molecular ion interferences at m/z 54 and 56 were reduced by 2 orders of magnitude. However, the interferences at m/z 57 increased by the same amount in the presence of Ca in solutions owing to the formation of ^40^Ca^16^ OH^+^ through reactions with H~2~ in collision cell, indicating that ^57^Fe was not suitable for the determination of Fe from otoliths. Results for ^56^Fe suffered significantly from interferences of Ca‐based molecular ions when the Ca concentration in solution exceeded 100 µg ml^−1^, for which matrix‐matched calibration was required for accurate determination. CCT with the aid of He/H~2~ cell gas proved to be very effective in eliminating the interferences (^40^Ar^14^N^+^ and ^40^Ca^14^N^+^) at m/z 54. Presence of Ca up to 300 µg ml^−1^ had virtually no effect on the ion signals of ^54^Fe, which with low background signals, afforded accurate determination of Fe from otoliths by using aqueous external standards. Copyright © 2007 John Wiley & Sons, Ltd.