A simplified analysis of dimethylarsinic acid by wavelength dispersive X-ray fluorescence spectrometry combined with a strong cation exchange disk

Abstract

Dimethylarsinic acid (DMA(V)) was pre-concentrated from water samples using a strong cation exchange (SCX) disk functionalized with sulfonic groups, before being analyzed by wavelength dispersive X-ray fluorescence spectrometry (WDXRF). The adsorption of DMA(V) occurred preferentially on the surface of the SCX disk, regardless of pH levels, probably due to interactions with the sulfonic functional groups. However, no other arsenic species, such as arsenate (iAs(V)), arsenite (iAs(III)), and monomethylarsonic acid (MMA(V)), were retained. The SCX-WDXRF method produced a strongly linear calibration curve (R-2 = 0.9996) with its limit of detection at 0.218 mu g L-1 when a one-liter water sample was used for pre-concentration. The As intensity of the system was sensitive to the Pb content retained on the SCX disk owing to the proximity of the As-K alpha and Pb-L alpha lines. To compensate for this interference, a correction factor was developed by considering the calibration slope ratio between the X-ray intensity measured at a Bragg angle of 48.781 degrees and the Pb content of the SCX disks. The results of spike tests for iAs(V), iAs(III), MMA(V), and DMA(V) with and without the addition of Pb in synthetic landfill leachate exhibited reasonable recoveries (i.e., 98-105%) after the spectral adjustment for the Pb interference. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.