Carol A. Brockhoff

A comparison of automated and traditional methods for the extraction of arsenicals from fish

An automated extractor employing accelerated solvent extraction (ASE) has been compared with a traditional sonication method of extraction for the extraction of arsenicals from fish tissue. Four different species of fish and a standard reference material, DORM-2, were subjected to both extraction methods. Arsenicals that were extracted with 50% (m/m) methanol-18 MΩ water were speciated with chromatographic separation and inductively coupled plasma mass spectrometric (ICP-MS) detection. Both extraction methods produced extraction efficiencies of greater than 71% with RSDs on replicates of less than 5.5%. The chromatographic separation employed a PRP-X100 anion exchange column. An ammonium nitrate and ammonium carbonate buffer at pH 9.0 was used to resolve five arsenicals. The speciation data indicates that the predominant species were arsenobetaine and arsenocholine. Two unknown arsenic species were present in most of the samples. The two extraction techniques produce similar relative distribution of arsenobetaine-arsenocholine (AsB-AsC) and dimethylarsinic acid (DMA) with relative area distributions of >95% and <2%, respectively.

Speciation of Arsenic Compounds in Drinking Water by Capillary Electrophoresis with Hydrodynamically Modified Electroosmotic Flow Detected Through Hydride Generation Inductively Coupled Plasma Mass Spectrometry With a Membrane Gas–Liquid Separator

Capillary electrophoresis (CE) was used to speciate four environmentally significant, toxic forms of arsenic: arsenite, arsenate, monomethylarsonic acid and dimethylarsinic acid. Hydride generation (HG) was used to convert the species into their respective hydrides. The hydride species were detected with inductively coupled plasma mass spectrometry. The HG unit utilized a microporous PTFE tube as a gas–liquid separator. The injection mode for CE was electrokinetic in conjunction with the novel use of hydrodynamically modified electroosmotic flow (HMEOF). In HMEOF, the electroosmotic flow is modified by applying hydrodynamic pressure opposite to the direction of the electroosmotic flow. HMEOF provides the capability of injecting increased quantities of analyte by offsetting the electroosmotic flow, which limits conventional electrokinetic injection. In order to correct for imprecisions in the electrokinetic injection in matrices of different ionic strength, the use of a surrogate for the injection of arsenic species was investigated. Germanium was investigated because it forms a hydride and has a low natural occurrence. The separation also utilized HMEOF, which allowed for greater freedom in buffer choice. The detection limits in distilled, de-ionized water were 25, 6, 9 and 58 ppt for the four species listed above, respectively. The detection limit was calculated from 3.14 σ n-1 of seven replicate injections and represents the precision of measuring the ratio of the area of the arsenic peaks to the area of a germanium surrogate peak. Standard addition was used to determine arsenate in drinking water samples. Recoveries of arsenite and arsenate from drinking water samples are reported using germanium as a surrogate to correct for sampling bias of the electrokinetic injection.

Determination of bromate in drinking waters by ion chromatography with inductively coupled plasma mass spectrometric detection

Abstract Bromate is a disinfection by-product in drinking water, formed during the ozonation of source water containing bromide. An inductively coupled plasma mass spectrometer is combined with an ion chromatograph for the analysis of bromate in drinking waters. Three chromatographic columns are evaluated in terms of detection limits, analysis time and tolerance to potentially interfering inorganic anions. The detection limits for all columns are in the 1–2 μg/l range for the direct analysis of bromate. A 5-min analysis time was achieved using a Dionex AG10 column and 100 mM NaOH as the eluent. Recoveries for bromate in fortified samples containing chloride (1000 ppm) or nitrate (50 ppm) were 96–107%. Recoveries for bromate in fortified samples containing sulfate (1000 ppm) were 91–124%. The R.S.D. values for drinking water analyses are in the 2–6% range. A 1.8-ml sample was preconcentrated on a Dionex AG10 column. This system produced bromate detection limits in the 0.1–0.2 μg/l range. Coupling the AG10 preconcentrator column with an ultrasonic nebulizer produced a detection limit of 50 ppt for bromate. The precision for samples which are preconcentrated is degraded due to an adjacent peak interfering with integration of the bromate peak.

Speciation of Selenium and Arsenic Compounds by Capillary Electrophoresis With Hydrodynamically Modified Electroosmotic Flow and On-line Reduction of Selenium(VI) to Selenium(IV) With Hydride Generation Inductively Coupled Plasma Mass Spectrometric Detection

Capillary electrophoresis (CE) with hydride generation inductively coupled plasma mass spectrometry was used to determine four arsenicals and two selenium species. Selenate (SeVI) was reduced on-line to selenite (SeIV) by mixing the CE effluent with concentrated HCl. A microporous PTFE tube was used as a gas-liquid separator to eliminate the 40Ar37Cl and 40Ar35Cl interference from 77Se and 75As, respectively. The direction of the electroosmotic flow during CE was reversed with hydrodynamic pressure, which allowed increased freedom of buffer choice. For conventional pressure injection, method detection limits for SeIV and SeVI based on seven replicate injections were 10 and 24 pg, respectively. Recoveries of SeIV and SeVI in drinking water were measured.

Speciation of arsenic compounds by ion chromatography with inductively coupled plasma mass spectrometry detection utilizing hydride generation with a membrane separator

Ion chromatography (IC) was used to speciate four of the environmentally significant, toxic forms of arsenic: arsenite, arsenate, monomethylarsonic acid, and dimethylarsinic acid. Hydride generation (HG) was used to convert the species to their respective hydrides. These hydride species were detected with ICP-MS. The gas–liquid separator for the HG unit was based on microporous PTFE tubing. Two novel features which reduce noise are incorporated into the membrane-based HG unit: firstly, gas is added to the liquid stream prior to entering the membrane, and secondly, the flow of carrier gas through the gas–liquid separator forms a ‘feedback’ loop. Absolute detection limits based on 3.14σ from 7 replicates for the four arsenic species listed above were 0.6, 3.1, 1.1, and 0.7 pg, respectively. The overall IC–HG–ICP-MS system produced RSD values of 1–6% over 30 min and 2–6% over a week for the four compounds. Two saline reference materials, NASS-4 and SLEW-2 (National Research Council of Canada), were analysed to determine concentrations of the four arsenic species, and the sum of the arsenic concentration was compared with the certified total arsenic value for each of the reference materials.

Arsenic determination in saline waters utilizing a tubular membrane as a gas–liquid separator for hydride generation inductively coupled plasma mass spectrometry

A tubular silicone rubber membrane is evaluated as a gas-liquid separator for the determination of arsenic in saline waters via HG-ICP-MS. The system was optimized in terms of NaBH4 and HCl concentrations. The intermediate gas and carrier gas were optimized in terms of sensitivity and stability. The pre-reduction of AsV in standard solutions and reference materials was investigated using KI and KI plus ascorbic acid sample treatments. The KI plus ascorbic acid treatment produced a similar response for AsIII and AsV independent of the matrix. The KI plus ascorbic acid treated samples could be held for 21 days without significant response changes. The detection limit was 92 pg based on 7 replicate injections of a 400 pg standard. The overall system was evaluated by analysing two reference materials, NASS-4 and SLEW-2. Precision and recovery data were collected on three estuarine samples.

Ultrasonic nebulization and arsenic valence state considerations prior to determination via inductively coupled plasma mass spectrometry

An ultrasonic nebulizer (USN) was utilized as a sample introduction device for an inductively coupled plasma mass spectrometer in an attempt to increase the sensitivity for As. The USN produced a valence state response difference for As. The AsIII response was suppressed approximately 20% relative to an AsV standard. This valence state response difference produced by the USN was investigated by collecting aerosol fractions and analysing these fractions by ion chromatography–ICP-MS. The analysis of these fractions indicated that AsIII could be oxidized to AsV as the aerosol traverses the USN. The fraction collected from the condenser drain of the USN was found to contain a disproportionate amount of As. The pre-nebulization oxidation of AsIII to AsVvia digestion, treatment with H2O2, and treatment with sodium hypochlorite were all investigated in terms of removing the valence state response difference of As. The treatment with 1 mg l–1 sodium hypochlorite was found to eliminate the valence state response difference for As without the need for digestion.