Evaluation of internal standards for inductively coupled plasma–mass spectrometric analysis of arsenic in soils

Abstract

Arsenic (As) is a common contaminant in soils, and analysis of soils by inductively coupled plasma–mass spectrometry (ICP‐MS) is often used to detect As in soil extracts. Internal standards (ISs) are part of ICP‐MS analyses to enhance precision and accuracy by compensating for instrument variability; however, an improper choice of IS can result in negative analytical bias. The goal of this study was to develop a protocol for evaluating ISs commonly used in ICP‐MS. Three soils of varying clay content and total As were extracted with a dilute electrolyte [0.005 mol L–1 Mg(NO3)2] and an acid digest. Arsenic concentrations were quantified by ICP‐MS using typical ISs: 6Li, 45Sc, 69Ga, 89Y, 103Rh, 115In, 159 Tb, and 209Bi. Standard addition was used as a benchmark for As quantification. The most consistent IS was 115In. Elevated, naturally occurring concentrations were detected for several of the ISs, particularly in the total digests, emphasizing the necessity for screening soils prior to analysis.

Atomic spectrometry update – a review of advances in environmental analysis

“…A reminder of the need to choose the correct IS for ICP-MS analysis was provided by Alvarado et al 196 who compared 6 Li, 45 Sc, 69 Ga, 89 Y, 103 Rh, 115 In, 159 Tb and 209 Bi for the determination of As in soil. Signicant analytical bias occurred when the 'native' concentration of the nuclide selected as IS in the soil digest approached or exceeded the concentration added.…”