Study On The Formation Process Of Oxide Ion And The Influence Of Carbon Matrix In Inductively Coupled Plasma Mass Spectrometry Using O-18-Labeled Arsenous Acid

To obtain further insight into the mechanism of carbon-induced signal enhancement of arsenic (As) at m/z = 75 in inductively coupled plasma mass spectrometry (ICP-MS), the formation process of arsenic oxide ion (AsO+) and the influence of carbon matrix on the process were investigated. The formation process of AsO+ was investigated using arsenous acid isotopically labeled with a highly enriched stable oxygen isotope O-18 ((H3AsO3)-O-18). (H3AsO3)-O-18 sample solutions with or without carbon matrix [i.e., 5% (v/v) isopropanol] were analyzed via ICP-MS, and axial intensity profiles of (AsO+)-As-75-O-18 and (AsO+)-As-75-O-16 in the ICP were obtained by measuring the signals at axial sampling positions from 3 to 28mm away from the load coil. Results suggested that AsO+ was formed via two different processes in the ICP: process 1, which involved the decomposition of As-containing molecules (i.e., H3AsO3) to AsO+, and process 2, which involved the recombination between As+ and oxygen originating from liquids introduced into the ICP (e.g., solvents) or gases (e.g., entrained atmospheric gases). In addition, results suggested that carbon matrix has the potential to enhance process 1.