Secondary ion mass spectrometry analysis of iron oxides with known ¹⁸ O/ ¹⁶ O contents

Iron oxide films with known 18 O and 16 O content were prepared by thermal oxidation of iron metal in H 2 18 O/H 2 16 O gas mixtures at 400°C. The oxide films were analysed in four laboratories with SIMS within a month after they were produced. One oxide sample (with 91% 18 O) was also analysed after storage in air for 15 months. It turns out that the oxides are stable over that time period. The yield ratios of the detected ionic species based on negative 18 O and 16 O ions and metal–oxygen‐containing ions were compared with the nominal, known values. The effect of interference of residual 16 O and 16 OH on the results is discussed and appropriate measures for reducing this effect are proposed. Reasonably good agreement is found between the four laboratories.