Development of LC-HGAFS method for direct measurement of monothioarsenate and application for its adsorption characteristics. (November 2020)

• Record Type: Journal Article
• Authors: Shan, Huimei; Liao, Danxue; Zhan, Hongbin; Peng, Sanxi; Zhang, Jinxian; Pan, Aoran
• Is Part Of: Applied geochemistry. Volume 122(2020)
• Publication Date: 2020-11
• Subjects: Monothioarsenate -- LC-HGAFS -- Measurement method -- Adsorption; Environmental geochemistry -- Periodicals; Water chemistry -- Periodicals; Geochemistry -- Social aspects -- Periodicals; Geochemistry -- Periodicals; 551.9
• DOI: 10.1016/j.apgeochem.2020.104708
• Languages: English
• ISSNs: 0883-2927

Abstract

Abstract: Thioarsenic is one of the major arsenic species recently detected in high-arsenic groundwater, and precise detection of thioarsenic is very important for understanding arsenic transport in the environment. However, the existing methods usually involve complicated operation procedures at a high cost. In this work, a cost-effective new method was developed for direct measurement of monothioarsenate (MTA) using Liquid Chromatography Hydride-Generation Atomic Fluorescence (LC-HGAFS), and it was applied to study MTA adsorption on the sand, soil, and goethite. The standard MTA sample was prepared using As2 O3, NaOH, and sulfur, and its purity was determined at different reaction temperatures to identify the thermal effect. Results showed that the major component of the prepared MTA sample was Na3 AsSO3 7H2 O and its purity was higher than 98% with only one impurity of arsenite. With the decrease of reaction temperature, the purity of the MTA sample decreased and both arsenite and arsenate impurities were present in samples. When MTA concentrations were at the range of 18–360 μg/L, it had an excellent linear relationship with the peak area with a coefficient determination ( R 2 ) greater than 0.9998 and an analytical detection limit of 33 μg/L. For three water samples containing different concentrations of arsenite, arsenate, and MTA, the relative errors between the detected and actual values were ranged from −0.11% to 8.21%. The adsorption of MTA on the sand, soil, and goethite reached equilibrium at 4 h, 8 h, and 8 h, respectively, and their maximum adsorption capacities were 122.47, 226.73 and 1979.75 μg/g, respectively. MTA adsorptions on sand and soil fitted well with Langmuir as well as Freundlich models, with R 2 values greater than 0.98 and 0.96, respectively. MTA adsorption on goethite fitted better into the Freundlich model with an R 2 value of 0.9863. Besides, the increasing pH values can suppress MTA adsorption on these three media because iron oxide is the major factor controlling the MTA adsorption on them. Highlights: A new method is firstly developed for direct measurement of MTA using LC-HGAFS. Analytical detection limit is 33 μg/L and the relative error is −0.11%~8.21%. MTA adsorption reaches equilibrium before its transformation in ambient conditions.