Determination of arsenic in samples with high chloride content by inductively coupled plasma mass spectrometry

Abstract

The arsenic content of samples with a high chloride content has been determined using inductively coupled plasma mass spectrometry (ICP-MS) with the addition of nitrogen to the carrier gas. With as little as 0.032 l min^–1 nitrogen in the argon carrier gas the level of the polyatomic ion, ⁷⁵ArCl⁺, which interferes in the determination of monoisotopic arsenic, is reduced to negligible levels. This modification is shown to be effective for the analysis of real samples, even for solutions which contain greater than 1% chloride. The presence of peaks at masses 49 and 51, when nitrogen is added, is attributed to ¹⁴N³⁵Cl⁺ and ¹⁴N³⁷Cl⁺, respectively. The arsenic content of reference materials, determined by nitrogen addition ICP-MS are in agreement with certificate values. Conventional argon-only ICP-MS values show an apparent 30% increase in arsenic owing to chloride interference. The nitrogen addition study has been extended to include a comparison of the total arsenic content of urine samples obtained from diet-controlled volunteers with the cumulative contribution from arsenic species determined by alternative coupled techniques.