Effect of methanol addition on generation of isobaric polyatomic ions in the analysis of arsenic with ICP-MS

Abstract

In the analysis of arsenic (As) with ICP-MS, it was observed that methanol addition to the sample decreases the amount of (ArCl+)-Ar-40-Cl-35 formed in the previous study. To investigate the effect of methanol addition on generation of isobaric polyatomic ions and its mechanism, a diluted HG solution and As solutions with varying concentrations of methanol (0, 1, 2, 3, and 4 v/v%) were analyzed using ICP-MS at a variety of mass spectra (m/z = 35, 47, 75, 82, 117, and 152). With addition of methanol to the sample, the signal intensity of (CCl+)-C-12-Cl-35 increased 11.1-fold while that of (ArCl+)-Ar-40-Cl-35 only increased 1.17-fold. In this regard, carbon atoms that are not ionized in the plasma (C-12) originated from methanol seemed to convert (ArCl+)-Ar-40-Cl-35 to (CCl+)-C-12-Cl-35 through the substitution reaction. Furthermore, carbon atoms ionized in the plasma (C-12(+)) converted As-75 into As-75(+) via the charge transfer reaction and thus increased signal intensity for As. At the same time, the amount of (ArCl+)-Ar-40-Cl-35 formed in the plasma decreased since the C-12 regenerated from C-12(+) during the charge transfer process can act as a reactant in the substitution reaction aforementioned. (C) 2016 Elsevier B.V. All rights reserved.