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

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 (As-Extraction (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 (As-Extraction 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, similar to0.04 mm particle size) produced near-quantitative removal of As(III) and As(V), while similar to90% of the MMA and similar to10% of the DMA was removed by the Filter Aid. This is contrary to the 99.6% +/- 0.8 (+/-2s) As-Extraction Recovery obtained for an AsB in a LFB. The ack of retention of AsB on the Filter Aid is consistent with the 94.8% +/- 11.8 (+/-2s) As-Extraction 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 As-Extraction Recovery of 70.0% +/- 9.8 (+/-2s). The low As-Extraction 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 As-Extraction Recovery in a LFB for Q-Beads was 98.7% +/- 5.6 (+/-2s). The As-Extraction Efficiency and the LFM As-Extraction Recovery from DORM-2 using Q-beads were 88.2% +/- 14.6 and 83.2% +/- 11.8 (+/-2s), respectively. Finally, two Teflon particle sizes were evaluated (250 mum and 1000 mum diameter) as dispersion media. The Teflon dispersion media produced LFB As-Extraction Recoveries of 98.7% +/- 3.4 (+/--2s) (for the 250 mum particle) and 95.2% +/- 3.6 (+/-2s) (for the 1000 mum particle). The As-Extraction (Efficiencies) for DORM-2 were 88.6% +/- 2.2 and 84.8% +/-- 2.2 (+/-2s) for the 250 mum and 1000 mm Teflon dispersion media, respectively. As-Extraction Recoveries of the LFMs for DORM-2 using the 250 mum and 1000 mum Teflon were 101.9% +/- 2.6 and 101.5% +/- 1.8 (+/-2s), 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 MOmega water required greater than 8 h. The slow resolubilization after the solvent reduction was not observed for the other analytes.