Determination of arsenic at a gold-plated carbon paste electrode using constant current stripping analysis

A new stripping method for the determination of arsenic in water samples with a gold film-plated carbon paste electrode has been developed for the use in constant current stripping analysis (CCSA). In the novelized procedure, differentiation between As(III) and chemically pre-reduced As(V), the effect of Cu(II) on the response of arsenic, and the stability of sample solutions were studied in detail. Compared to the voltammetric approach, the method utilizing CCSA offers a more rapid procedure with improved analytical characteristics such as reproducibility, selectivity over the Cu(II) ions, or lower detection limit (3 ppb for As(III) and 0.5 ppb for As(V), respectively). The possibilities of the optimized method are demonstrated by determinations of As(III), As(V), and total arsenic in samples of polluted river water.     

A rapid method of sample preparation for determining arsenic in water by stripping voltammetry

A procedure was developed for sample preparation for the further determination of arsenic in potable and natural water and process solutions by stripping voltammetry (SV). To minimize the losses and simplify the procedure, arsenic(III) was oxidized by the ozonation or UV irradiation of the solution in the presence of sulfite, chloride, or hydroxide ions, which increased the oxidation efficiency. The time required for 100% oxidation does not exceed 60 s for an arsenic concentration of no more than 1 mg/L. The reduction to arsenic(III) was performed photochemically in the presence of sodium sulfite for 5 min. Further stripping voltammetric determination was performed in the same solution using a gold-plated carbon electrode. The developed procedure is rapid, simple, and easy-to-automate.     

Anodic-stripping voltammetric determination of arsenic at a copper-coated glassy-carbon electrode

The anodic-stripping voltammetric behaviour of arsenic(III) at a glassy-carbon electrode copper-coated in situ has been investigated. The effects of copper concentration, acidity, deposition potential and sweep rate on the stripping peak have been examined and criteria are given for the choice of experimental conditions. The procedure is applicable to the determination of 7.5-750 ng/ml of arsenic levels and is useful for the analysis of various types of water sample.     

Simple and Highly Selective Catalytic Adsorptive Voltammetric Method for Cr(VI) Determination

A simple and highly selective and sensitive catalytic adsorptive stripping voltammetric procedure for determination of traces of Cr(VI) in the presence of a large excess of Cr(III) in environmental water samples is reported. To obtain a low detection limit the voltammetric procedure of chromium determination in the presence of DTPA and nitrate was exploited. For elimination of interference of Cr(III) ethylenediaminedisuccinic acid was used as a masking agent. At optimized conditions the calibration graph is linear from 2×10^?10 to 2×10^?8 mol L^?1 for accumulation time of 30 s. The validation of the procedure was performed by comparison of the results of analysis of river water samples with those obtained using other accepted voltammetric procedure.     

Water Quality in Watercourses of the Transboundary Narva River Basin

A procedure has been developed for the assessment of transboundary river water quality. The procedure is based on the calculation of the chemical index and classification of water quality. The quality of river waters is assessed by measuring a set of chemical parameters in water samples, followed by data representation in the form of the chemical index CJ which characterizes generalized water quality. A classification system has been proposed for the estimation of contamination of transboundary water bodies on the basis of a “broken bar” model. Using the developed procedure, year-to-year, within-year, and seasonal dynamics of water quality in watercourses of the transboundary Narva River basin have been determined.     

Redox Speciation of Inorganic Arsenic in Water and Saline Samples by Adsorptive Cathodic Stripping Voltammetry in the Presence of Sodium Diethyl Dithiocarbamate

This paper describes a new voltammetric procedure for the inorganic speciation of As(III) and As(V) in water samples. The procedure is based on the chemical reduction of arsenate [As(V)] to arsenite [As(III)] followed by the voltammetric determination of total arsenic as As(III) at the hanging mercury drop electrode (HMDE) by adsorptive cathodic stripping voltammetry (AdCSV) in the presence of sodium diethyl dithiocarbamate (SDDC). The reduction step involved the reaction with a mixture of Na₂S₂O₅ and Na₂S₂O₃ in the concentrations 2.5 and 0.5 mg mL^?1, respectively, and the sample heating at 80 °C for 45 min. The linear range for the determination of total arsenic as As(III) in the presence of SDDC was between 5 and 150 μg L^?1 for a deposition time of 60 s (r=0.992). A detection limit of 1.05 μg L^?1 for total As was calculated for the method in water samples using a deposition time of 60 s. The detection limits of 4.2 μg L^?1 and 15.0 μg L^?1 for total As in seawater and dialysis concentrates, respectively, were calculated using a deposition time of 60 s. The relative standard deviations calculated were 2.5 and 4.0% for five measurements of 20 μg L^?1 As(V) as As(III) in water and dialysis concentrates, respectively, after chemical reduction under optimized conditions. The method was applied for the determination of As(III) and total As in samples of dialysis water, mineral water, seawater and dialysis concentrates. Recovery values between 86.0 and 104.0% for As(III) and As(V) added to the samples prove the satisfactory accuracy and applicability of the procedure for the arsenic monitoring.     

Speciation of arsenic(V) and arsenic(III) by cathodic stripping voltammetry in fresh water samples

A voltammetric stripping procedure is described for the determination of arsenic(V) in a mannitol-sulphuric acid medium. The arsenic is coprecipitated with copper and selenium and reduced to arsine at the hanging mercury drop electrode. Using an accumulation time of 240 s, the detection limit is 0.52 μg L^–1, the determination limit is 0.9 μg L^–1. The method has been applied to the determination of arsenic in water samples. By varying the composition of the supporting electrolyte it is possible to differentiate between arsenic(III) and arsenic(V). As both oxidation states have different toxicological characteristics, the ability to discriminate between both is an distinct advantage of the proposed method. Received: 25 October 1996 / Revised: 7 February 1997 / Accepted: 12 February 1997     

Voltammetric determination of copper in water samples digested by ozone

The applicability of ozone as a digestion agent in voltammetric trace metal analysis of water samples was investigated. It was shown that ozone efficiently destroys dissolved organic matter, causing a significant decrease of the concentration of surface active substances in the sample, thus enabling voltammetric measurements. Ozonolysis times of 30 and 60 min were sufficient for the treatment of river water and biologically treated wastewater samples, depending on their organic load, prior to voltammetric determination of copper using a solid gold electrode.     

Biomethylation of Arsenic in an Arsenic-rich Freshwater Environment

Arsenic circulation in an arsenic-rich freshwater ecosystem was elucidated to detect arsenic species in the river water and in biological samples living in the freshwater environment. Water-soluble arsenic compounds in biological samples were extracted with 70% methanol. Samples containing arsenic compounds in the extracts were treated with 2 mol dm³ of sodium hydroxide and reduced with sodium borohydride. The detection of arsenic species was accomplished using a hydride generation/cold trap/cryofocus/gas chromatography-mass spectrometry (HG/CT/CF/GC-MS) system. The major arsenic species in the river water, freshwater algae and fish are inorganic arsenic, dimethylarsenic and trimethylarsenic compounds, respectively. Trimethylarsenic compounds are also detected in aquatic macro-invertebrates. The freshwater unicellular alga Chlorella vulgaris, in a growth medium containing arsenate, accumulated arsenic and converted it to a dimethylarsenic compound. The water flea Daphnia magna, which was fed on arsenic-containing algae, converted it to a trimethylarsenic species. © 1997 by John Wiley & Sons, Ltd.     

Simultaneous Determination of Chromium(VI) and Aluminum(III) by Adsorptive Stripping Voltammetry with Pyrocatechol Violet

A new methodology is presented for the simultaneous determination of chromium(VI) and aluminum(III) by differential‐pulse adsorptive stripping voltammetry (DPAdSV) with Pyrocatechol Violet (PCV) as a complexing agent. In this procedure, a partial least‐squares regression (PLS) is used for the resolution of the strongly overlapping voltammetric signals from mixtures of Cr^VI and Al^III in the presence of PCV. The procedure was successfully applied to the determination of these metals in river water.     

Use of Multiple Square Wave Voltammetry for the Detection of Diquat Herbicide in Environmental Water,Foods and River Sediments

This paper reports the use of multiple square wave voltammetry (MSWV) in the development of a simple, sensitive, fast and low-cost electroanalytical procedure for the diquat herbicide detection in different samples employing a custom-made gold microelectrode (Au-ME). The experimental and voltammetric parameters were optimized, and the use of eight pulses superimposed in each step in the MSWV yielded the detection limits two orders of magnitude greater than those obtained by SWV or previously published chromatographic procedures. Also, the Au-ME allied to MSWV was used to determine diquat in beetroot, onion, peach, environmental water and river sediments. All samples were spiked, and the obtained recovery percentage values were satisfactory for the analytical procedure, showing that Au-ME and MSWV is a suitable tool for diquat residues detection in complex samples.     

Preconcentration by coprecipitation of arsenic and tin in natural waters with a Ni-pyrrolidine dithiocarbamate complex and their direct determination by solid-sampling atomic-absorption spectrometry

A method for the determination of trace amounts of arsenic and tin in natural waters is described. Trace amounts of arsenic and tin were preconcentrated by coprecipitation with a Ni-ammonium pyrrolidine dithiocarbamate (APDC) complex. The coprecipitates obtained were directly analyzed by graphite-furnace atomic-absorption spectrometry (GFAAS) using the Ni-APDC complex solid-sampling technique. The coprecipitation conditions used for the trace amounts of arsenic and tin in natural water were investigated in detail. It was found that arsenic and tin at sub-ng mL(-1) levels were both coprecipitated quantitatively by Ni(PDC)2 in the pH range 2-3. The concentration factors by coprecipitation reached approximately 40,000 when 2 mg nickel was added as a carrier element to 500 mL of the water sample. The proposed method has been applied to the determination of trace amounts of arsenic and tin in river water and seawater reference materials, and the detection limits for arsenic and tin, which were calculated from three times of the standard deviation of the procedural blanks, are 0.02 ng mL(-1) and 0.04 ng mL(-1), respectively, for 500-mL volumes of water sample.     

Voltammetric measurement of arsenic in natural waters

There are several U.S. EPA approved methodologies for the determination of arsenic in ground water. Such technologies are lab-based, time intensive and can lead to a large capital cost for multi-sample analysis. In light of the number of sites found to contain arsenic at levels higher than the maximum contaminant level (MCL), on-site screening and monitoring systems are an attractive alternative. This review article summarizes several examples in the recent literature to illustrate the breadth of work in voltammetric analysis of arsenic in environmental samples. Also, included are recent voltammetric results, obtained with a microfabricated gold array and a field portable potentiostat, at an arsenic contaminated site in southern New Jersey.     

Arsenic Speciation in Sargassum fusiforme by Microwave-Assisted Extraction and LC-ICP-MS

Sargassum fusiforme, the common Chinese edible seaweeds, was investigated for total arsenic concentration by ICP-MS and for individual arsenic species by LC-ICP-MS. For this purpose, a microwave-assisted procedure was used for the extraction of arsenic species in freeze-dried seaweed and an analytical procedure for the sensitive and efficient speciation of the arsenic species As(III), dimethylarsinic acid, monomethyl arsonic acid, As(V), arsenobetaine and arsenocholine was optimized. Arsenic compounds were extracted from the seaweed with a methanol/water mixture; the extracts were evaporated to dryness, redissolved in water, and chromatographed on an anion exchange column. The arsenic species in Sargassum fusiforme are abundant. In some sample, the majority of arsenic compounds detected in the extracts were inorganic species, with a predominance of As (V). In addition, some significant amounts of unidentified arsenic compounds were also observed in the extracts.

     

Effective UV photolytic decomposition of organic compounds with a low-pressure mercury lamp as pretreatment for voltammetric analysis of trace metals

The effectivity of UV irradiation with low and high pressure mercury (L-Hg and H-Hg) lamps on the decomposition of organic compounds in aqueous solutions, as pretreatment for the voltammetric determination of trace metals, is compared. The photolytic decomposition with the L-Hg lamp was much faster than with the H-Hg lamp. The higher efficiency of the L-Hg lamp is caused by its greater light intensity at short wavelengths. Interferences of organic compounds on the voltammetric determination of nickel and indium were eliminated successfully by 90 min irradiation with the L-Hg lamp. Humic acid and organic interference with the voltammetric determination of nickel in natural river water were successfully eliminated. The decomposition using the L-Hg lamp can be carried out without added oxidizing reagents and at room temperature, thus eliminating loss of water samples by evaporation at higher temperature.     

Preconcentration by coprecipitation of arsenic and tin in natural waters with a Ni–pyrrolidine dithiocarbamate complex and their direct determination by solid-sampling atomic-absorption spectrometry

A method for the determination of trace amounts of arsenic and tin in natural waters is described. Trace amounts of arsenic and tin were preconcentrated by coprecipitation with a Ni–ammonium pyrrolidine dithiocarbamate (APDC) complex. The coprecipitates obtained were directly analyzed by graphite-furnace atomic-absorption spectrometry (GFAAS) using the Ni–APDC complex solid-sampling technique. The coprecipitation conditions used for the trace amounts of arsenic and tin in natural water were investigated in detail. It was found that arsenic and tin at sub-ng mL^–1 levels were both coprecipitated quantitatively by Ni(PDC)₂ in the pH range 2–3. The concentration factors by coprecipitation reached approximately 40,000 when 2 mg nickel was added as a carrier element to 500 mL of the water sample. The proposed method has been applied to the determination of trace amounts of arsenic and tin in river water and seawater reference materials, and the detection limits for arsenic and tin, which were calculated from three times of the standard deviation of the procedural blanks, are 0.02 ng mL^–1 and 0.04 ng mL^–1, respectively, for 500-mL volumes of water sample.     

Utilization of Carbon Paste Electrodes for the Voltammetric Determination of Chlortoluron

Conventional (CPE) and miniaturized (m‐CPE) carbon paste electrodes consisting of a carbon paste filled capillary were used for differential pulse voltammetric determination of chlortoluron in samples of river water and soil, in the latter case after the extraction by methanol. Britton‐Robinson buffer pH 3 with low content of methanol was found to be optimal for the determination. The achieved determination limits were 2.8 µmol L^?1 and 0.34 µmol L^?1 in river water, and 3.1 and 4.3 µg g^?1 in soil, using CPE and m‐CPE, respectively.     

Speciation of arsenic in water,sediment, and plants of the Moira watershed,Canada, using HPLC coupled to high resolution ICP-MS

High-performance liquid chromatography (HPLC) coupled with high-resolution sector field ICP-MS was applied to the speciation of arsenic in environmental samples collected from the Moira watershed, Ontario, Canada. Arsenic contamination in Moira River and Moira Lake from historic gold mine operations is of increasing environmental concern to the local community. In this study, the current arsenic contamination status in water, sediment, and plants was investigated. Elevated levels of arsenic in the surface water of up to 75 ng mL(-1) in Moira River and 50 ng mL(-1) in Moira Lake were detected, 98% of which was present as arsenate. High concentrations of arsenic (>300 ng mL(-1)), mainly present as arsenite, were detected in sediment porewaters. A sediment profile of As from the West basin of Moira Lake showed lower As concentrations compared with data from the 1990s. An optimized extraction procedure using a phosphoric acid-ascorbic acid mixture demonstrated that an unknown "As-complex" which may consist of As, sulfide and organic matter is potentially responsible for the release of arsenite from the sediment to the overlying water column. Arsenic concentrations in plant samples ranged from 2.6 to 117 mg kg(-1), dry weight. Accumulation of arsenic was observed in submerged plants collected from Moira River and Moira Lake. Only a small part of the arsenic (6.3-16.1%) in the plants was extractable with methanol-water (9:1), and most of this arsenic (70-93%) was inorganic arsenic. A variety of organic arsenic compounds, including simple methylated compounds (methylarsonic acid and dimethylarsinic acid), trimethylarsine oxide, and tetramethylarsonium cation were detected at trace levels. No arsenobetaine and arsenocholine was found in any plant sample. An unknown compound, most probably an arsenosugar was detected in the two submerged plants, coontail ( Ceratophyllum demersum) and long-stemmed waterwort ( Elatine triandra). These submerged plants are constantly exposed to high arsenic concentrations in the surrounding water. Apparently, they are able to grow in this environment without invoking the same biochemical defence known from marine algae to detoxify inorganic arsenic. The detoxification mechanism of these plants remains unknown.     

Modification of catalytic adsorptive stripping voltammetric method of hexavalent chromium determination in the presence of DTPA and nitrate

The voltammetric procedure for determination of traces of Cr(VI) [Anal. Chim. Acta (1992) 262:103] was modified by changing the temperature of the measurements. It was found that at the temperature of 40 °C the time of decrease of the Cr(III) signal was shortened from 30 to 5 min. As a result the total analysis time was drastically shortened. The modified procedure does not show any disadvantage as compared to the original method. The results of Cr(VI) determination by the modified procedure are less affected by Cr(III) as compared to the original method. The detection limit of the method was 2.5 × 10^-11 mol L^-1 (1.2 ng L^-1). The validation of the modified procedure was performed by comparison of the results of analyses of tap and river water samples with those obtained using original procedure.     

Adsorptive voltammetric determination of copper as its nioximate complex

A sensitive and selective stripping voltammetric ultratrace determination of copper is described, based on adsorptive accumulation of the cu(II)-nioxime complex on the surface of a hanging mercury drop electrode, followed by the reduction of the adsorbed complex during the cathodic scan. The analytical conditions for the determination of copper by differential-pulse and linear-scan absorption voltammetry have been optimized. The method is compared to the routine anodic stripping voltammetric method for copper. Its applicability to river and potable water analysis is illustrated. The detection limit, restricted by the blank, is about 0.5 microg/l.; the relative standard deviation (at microg/l. level) for a standard solution is below 5% and for water samples is 5-9%.