An evaluation of sample dispersion media used with accelerated solvent extraction for the extraction and recovery of arsenicals from LFB and DORM-2

Abstract

An accelerated solvent extraction (ASE) device was evaluated as a semi-automated means for extracting arsenicals from quality control (QC) samples and DORM-2 [a standard reference material (SRM)]. Unlike conventional extraction procedures, the ASE requires that the sample be dispersed in an inert dispersion media prior to the extraction. The need to disperse the sample in a support matrix prior to extraction is demonstrated by a 58% reduction in the extraction efficiency of arsenic (AsExtraction Efficiency) from DORM-2 if the sample is not homogeneously suspended in the dispersion media. Three dispersion media (Filter Aid, Q-Beads, Teflon) were evaluated in terms of the arsenic extraction recoveries (AsExtraction Recovery) from laboratory fortified blanks (LFB) and matrices (LFM). The arsenicals investigated were arsenobetaine (AsB), arsenite [As(III)], dimethylarsinic acid (DMA), disodium methylarsenate (MMA) and arsenate [As(V)]. The first dispersion medium, Filter Aid (a high density glass bead, ∼0.04 mm particle size) produced near-quantitative removal of As(III) and As(V), while ∼90% of the MMA and ∼10% of the DMA was removed by the Filter Aid. This is contrary to the 99.6% ± 0.8 (±2σ) AsExtraction Recovery obtained for an AsB in a LFB. The lack of retention of AsB on the Filter Aid is consistent with the 94.8% ± 11.8 (±2σ) AsExtraction Efficiency for DORM-2 which contains predominately AsB. Fortifying DORM-2 with an AsB, As(III), As(V), MMA and DMA mixture produces a LFM AsExtraction Recovery of 70.0% ± 9.8 (±2σ). The low AsExtraction Recoveries are a result of the Filter Aid binding and retaining certain anionic arsenicals. The second dispersion media, Q-beads (a soda lime glass bead, 0.8 mm spherical), did not exhibit these binding interactions. The AsExtraction Recovery in a LFB for Q-Beads was 98.7% ± 5.6 (±2σ). The AsExtraction Efficiency and the LFM AsExtraction Recovery from DORM-2 using Q-beads were 88.2% ± 14.6 and 83.2% ± 11.8 (±2σ), respectively. Finally, two Teflon particle sizes were evaluated (250 µm and 1000 µm diameter) as dispersion media. The Teflon dispersion media produced LFB AsExtraction Recoveries of 98.7% ± 3.4 (±2σ) (for the 250 µm particle) and 95.2% ± 3.6 (±2σ) (for the 1000 µm particle). The AsExtraction Efficiencies for DORM-2 were 88.6% ± 2.2 and 84.8% ± 2.2 (±2σ) for the 250 µm and 1000 µm Teflon dispersion media, respectively. AsExtraction Recoveries of the LFMs for DORM-2 using the 250 µm and 1000 µm Teflon were 101.9% ± 2.6 and 101.5% ± 1.8 (±2σ), respectively. ASE cell components and the ASE solvent reduction vials were evaluated for potential analyte losses. The stainless steel frit located at the exit of the ASE cell was found to bind up to 13% of the arsenicals present in a LFB. The resolubilization of As(III) from the Pyrex ASE vials using 18 MΩ water required greater than 8 h. The slow resolubilization after the solvent reduction was not observed for the other analytes.