Ultrasonic nebulization and arsenic valence state considerations prior to determination via inductively coupled plasma mass spectrometry

Abstract

An ultrasonic nebulizer (USN) was utilized as a sample introduction device for an inductively coupled plasma mass spectrometer in an attempt to increase the sensitivity for As. The USN produced a valence state response difference for As. The As^III response was suppressed approximately 20% relative to an As^V standard. This valence state response difference produced by the USN was investigated by collecting aerosol fractions and analysing these fractions by ion chromatography–ICP-MS. The analysis of these fractions indicated that As^III could be oxidized to As^V as the aerosol traverses the USN. The fraction collected from the condenser drain of the USN was found to contain a disproportionate amount of As. The pre-nebulization oxidation of As^III to As^Vvia digestion, treatment with H₂O₂, and treatment with sodium hypochlorite were all investigated in terms of removing the valence state response difference of As. The treatment with 1 mg l^–1 sodium hypochlorite was found to eliminate the valence state response difference for As without the need for digestion.