Trace determination of arsenic species by capillary electrophoresis with direct UV detection using sensitivity enhancement by counter‐ or co‐electroosmotic flow stacking and a high‐sensitivity cell

Abstract

Stacking techniques used independently and also with a high-sensitivity cell (HSC) were employed to optimise sensitivity and detection limits in the direct photometric detection of the following eight arsenic species by capillary zone electrophoresis (CZE): arsenite, arsenate, monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), 4-hydroxy-3-nitrophenylarsonic acid (Roxarsone), p-aminophenylarsonic acid (p-ASA), 4-nitrophenylarsonic acid (4-NPAA), and phenylarsonic acid (PAA) (target analytes). The stacking mechanisms, optimised stacking and separation conditions, and concentration sensitivity enhancement factors were discussed and compared for (i) normal stacking mode (NSM, sometimes also referred to as field-amplified stacking) in an uncoated fused-silica capillary in the counter-electroosmotic flow (EOF) mode, (ii) large-volume sample stacking (LVSS) with polarity switching, and (iii) the less often applied stacking method of co-EOF NSM stacking with EOF reversal using a poly(diallydimethylammonium chloride) (PDDAC)-coated capillary. The optimal injection volumes were 7.4, 60 and 17.2% of the total capillary volume, for the above three methods, respectively. LVSS with polarity switching gave the lowest limit of detection (LOD). The use of the HSC further reduced the LOD of each target analytes by a factor of 5-8 times. By combining LVSS and HSC, LODs of the target analytes could be reduced by a factor of 218-311, to 5.61, 9.15, 11.1, and 17.1 microg/L for As(III), DMA, MMA, and As(V), respectively. The method was demonstrated to be applicable to the determination of the target analytes in tap water and lake water, with recoveries in the range of 89.4-103.3%.

CZE for the speciation of arsenic in aqueous soil extracts

“…Because the detection limits achieved with CZE-UV are in the low milligram per liter range and hence mostly not sufficient for the determination of the analytes in real environmental samples, many authors used spiked samples for the investigation of arsenic speciation [10,[11][12][13]. Stacking of the analytes in the capillary can improve the detection limits.…”

“…The method was applied to the determination of four phenylarsenic compounds in spiked chicken-feed samples. Another work of Sun et al [11] describes the application of various stacking methods for the determination of phenylarsenic compounds in spiked tap water and lake water samples. Besides the implementation of stacking techniques, another method to enhance detection limits is the use of a more powerful detector.…”

On-line Sample Preconcentration by Large-volume Sample Stacking with an Electroosmotic Flow Pump (LVSEP) in Microscale Electrophoresis

“…This was originally developed by Burgi, who used diethylenetriamine (DETA) as an additive to reduce the EOF. 16 In previous LVSS reports, cationic-surfactants system [16][17][18][19][20][21][22][23][24][25][26][27] or a non-aqueous CE (NACE) mode [28][29][30][31][32] were mainly employed to obtain a slower anodic EOF. Despite that the first LVSS study 16 tried to inject a low-conductivity sample into the whole capillary to obtain a higher concentration efficiency, most LVSS studies have involved optimization of the injection length to be compatible with both the sensitivity and the resolution.…”

Arsenic Speciation Analysis by Ion Chromatography - A Critical Review of Principles and Applications

“…However, its low amount of analyte mass applied in combination with low sensitivity detectors provides insufficient DL. For the most common As-species, DL of 5-17 μg/L were reached [117], detecting with a high sensitivity UV-cell and high sample volume stacking. In situ heteropolyacid formation with molybdate and UV-detection gave similar DL [118].…”