Gold Nanoparticle Modified Electrodes Show a Reduced Interference by Cu(II) in the Detection of As(III) Using Anodic Stripping Voltammetry

Interference by Cu(II) causes serious problems in the detection of As(III) using anodic stripping voltammetry at gold electrodes. The behavior of Cu(II) and As(III) were examined at both a gold macro electrode and two kinds of gold nanoparticle modified electrodes, one where gold particles are deposited on glassy carbon (GC) and the other where basal plane pyrolytic graphite (BPPG) is the substrate. The sensitivity of As(III) detection was higher on gold nanoparticle modified electrodes than those on a macro gold electrode by up to an order of magnitude. In addition, the stripping peak of As(III) was narrower and more symmetric on a gold nanoparticle‐modified GC electrode, leading to analytical data with a lower limit of detection. At a macro gold electrode, the peak currents of Cu(II) were higher than those on gold nanoparticle modified electrodes. Accordingly, through the use of gold nanoparticle modified electrodes, the effect of copper interference to the arsenic detection can be reduced.     

Photometric measurement of trace As(III) and As(V) in drinking water

A simple, fast and sensitive light-emitting diode (LED)-based photometric method for the differential determination of ppb-ppm levels of As(III) and As(V) in potable water in the presence of ppm levels of phosphate was developed. The detection chemistry is based on the well-known formation of arsenomolybdate, followed by reduction to heteropoly blue. The front-end of the measurement system is configured to selectively retain P(V) and As(V), based on the considerable difference of the pK(a) of the corresponding acids relative to As(III). Thus, it is As(III) that is injected into the medium, oxidized in-line with KBrO(3) to As(V) and forms Mo-blue that is detected by an LED-based detector. Only As(III) is measured if the sample is injected as such; if all As in the sample is prereduced to As(III) (by the addition of cysteine, in a provided in-line arrangement), the system measures As(V)+As(III). In the present form, limit of detection (LOD) (S/N=3) is less than 8 mug l(-1) As, and the linear range extends to 2.4 mg l(-1). Potential interference from dissolved silica and Fe(III) is eliminated by the addition of NaF to the sample.     

Electrochemical determination of arsenite in neutral media on reusable gold nanostructured films

We report a simple and novel method of stirring-only-driven accumulation and electrochemical determination of arsenite (As(III)) with both of the oxidation and reduction peaks associated with As(0)/As(III) using a gold nanofilm electrode in neutral solution. Under stirring, a large amount of As(III) was deposited on the modified electrode and the electrochemical response was greatly amplified. The accumulated As(III) on the electrode showed well-defined redox couple in 0.1 M blank phosphate buffer solution (pH 7.0), which could be used for the measurement of As(III). Under optimal conditions, As(III) could be detected in the range from 0.20 to 375 ppb with a detection limit of 0.04 ppb. In particular, with the use of the reduction peak of As(III) the modified electrode exhibits excellent performance for As(III) determination even in the presence of abundant Cu(II). The regeneration of the electrodes is facile with good reproducibility. The electrochemical system was applied to analyze As(III) in lake water, As(III) spiked tap water and drinking water.     

Screen Printed Carbon Electrode Modified with Poly(L‐Lactide) Stabilized Gold Nanoparticles for Sensitive As(III) Detection

Poly(L ‐lactide) stabilized gold nanoparticles (designated as PLA–Au^NP) with an average particle size of ca. 10 nm were used to modify a disposable screen‐printed carbon electrode (SPE) for the detection of As(III) by differential pulse anodic stripping voltammetry. Gold modification was evaluated by cyclic voltammetry, whereas scanning electron microscopy and transmission electron microscopy revealed the size and distribution of gold nanoparticles. The PLA–Au^NP/SPE was applied effectively to detect toxic As(III) in HCl medium. Under the optimal experimental conditions, a linear calibration curve up to 4 ppm with a detection limit (S/N=3) of 0.09 ppb was obtained. The sensitivity was good enough to detect As(III) at levels lower than the current EPA standard (10 ppb). Most importantly, the PLA–Au^NP/SPE can be tolerable from the interference of Cu, Cd, Fe, Zn, Mn, and Ni and hence provides a direct and selective detection method for As(III) in natural waters. Practical utility of the PLA–Au^NP/SPE was demonstrated to detect As(III) in “Blackfoot” disease endemic village groundwater from southwestern coast area of Taiwan (Pei‐Men).     

Atomic fluorescence spectrometric determination of trace amounts of arsenic and antimony in drinking water by continuous hydride generation

A highly sensitive and simple method has been developed for the determination of As(III), total As, Sb(III) and total Sb in drinking water samples by continuous hydride generation and atomic fluorescence spectrometry (HGAFS). For As determination, water samples aspirated in a carrier of 2 mol l(-1) HCl were merged with a reducing NaBH(4) 3%(m/v) solution, with sample and NaBH(4) flow rates of 12.5 and 1.5 ml min(-1) respectively. The hydride generated in a 170 cm reaction coil was transported to the detector with an Ar flow of 400 ml min(-1), and a limit of detection between 5 and 20 ng l(-1) was obtained. For Sb determination, 2.5 mol l(-1) HCl and 2%(m/v) NaBH(4) were employed, with respective flow rates of 9.7 and 2 ml min(-1). The hydride generated in a 50 cm reaction coil was transported to the detector with an Ar flow rate of 300 ml min(-1), and a limit of detection between 6 and 14 ng l(-1) was obtained. Determination of the total concentration of these elements was obtained after a previous reduction with KI. Recovery studies of different added concentrations of these species in natural water samples were between 93 and 104% for As(III), 96-103% for As(V), 93-101% for Sb(III) and 90-119% for Sb(V).     

An ion imprinted electrochemical sensor based on flower-like gold nanoparticles for the detection of trace arsenic(III) ions in water and food samples

A selective and sensitive electrode based on Au−S bonds between As(III) ion-imprinted polymer (IIP) and the flower-like gold nanoparticles (FL-AuNPs) had been rationally developed for detecting As(III) by using the square wave voltammetry (SWV) method. Under optimized measurement conditions, the prepared electrochemical sensor exhibited obvious detection performance of As(III) in the range of 0.009 μg/L–0.50 μg/L with a relatively low detection limit of 0.015 μg/L. Furthermore, the imprinted electrochemical sensor displayed good reusability, excellent specificity, and demonstrated high potential for environmental control with a recovery rate between 80.7 % and 113.3 %.     

Detection of As(III) via oxidation to As(V) using platinum nanoparticle modified glassy carbon electrodes: arsenic detection without interference from copper

The electrochemical detection of As(III) was investigated on a platinum nanoparticle modified glassy carbon electrode in 1 M aqueous HClO4. Platinum nanoparticle modified glassy carbon electrodes were prepared by potential cycling in 0.1 M aqueous KCl containing 1 mM K2PtCl6. In each potential cycle, the potential was held at + 0.5 V for 0.01 s and at -0.7 V for 10 s. 25 cycles were optimally used to prepare the electrodes. The resulting electrode surfaces were characterized with AFM. The response to arsenic(III) on the modified electrode was examined using cyclic voltammetry and linear sweep voltammetry. By using the As(III) oxidation peak for the analytical determination, there is no interference from Cu(II) if present in contrast to the other metal surfaces (especially gold) typically used for the detection of arsenic; Cu(II) precludes the use of the As(0) to As(III) peak for quantitative anodic stripping voltammetry measurements due to the formation of Cu3As2 and an overlapping interference peak from the stripping of Cu(0). After optimization, a LOD of 2.1 +/- 0.05 ppb was obtained using the direct oxidation of As(III) to As(V), while the World Health Organization's guideline value of arsenic for drinking water is 10 ppb, suggesting the method may have practical utility.     

Potentiometric Stripping of Arsenic(III) Using a Wall‐Jet Flow Cell and Gold(III) Solution as Chemical Reoxidant

In the proposed method As(III) is determined with a wall‐jet flow cell by means of potentiostatic co‐deposition of Au(III) and As(III) at a glassy‐carbon electrode and subsequent chemical stripping with Au(III). Factors affecting sensitivity and precision including acidity, Au(III) concentration, electrodeposition potential and flow rate were optimized. Optimum determination of As(III) in solutions containing 160 mg L^?1 and 1.2 M hydrochloric acid was accomplished with an electrolysis potential of ?0.1 V (vs. Ag/AgCl) and a flow rate of 0.59 mL min^?1. Different linear concentration ranges were achieved under these conditions with good precision and relative standard deviations between 6–9%. The detection limit obtained after 120 s of electrolysis was 0.55 μg L^?1.     

Synthesis hexagonal ß-Ni(OH)2 nanosheets for use in electrochemistry sensors

A new method for the determination of inorganic arsenic species (As(III) and As(V)) was developed by dispersive liquid-liquid microextraction (DLLME) separation and graphite furnace atomic absorption spectrometry (GFAAS) detection. In the pH range of 3–5, As(III) complexes with ammonium pyrrolidinedithiocarbamate (APDC) and then can be extracted into carbon tetrachloride droplets formed by injecting the binary solution of carbon tetrachloride (extraction solvent) and methanol (dispersive solvent) into the sample solution. As(V) is not extracted at the same pH conditions and remained in the aqueous phase. After extraction and phase separation by centrifugation, the enriched As(III) in the sedimented phase was determined by GFAAS. Total inorganic arsenic was determined after reduction of As(V) to As(III) with sodium thiosulfate and potassium iodide, and As(V) was calculated by difference. Under optimized conditions, the detection limits of this method for As(III) were 36 ng L^?1 with an enrichment factor of 45, and the relative standard deviation (R.S.D.%) was 3.1% (n?=?11, c?=?1.0 ng mL^?1). The method has been applied to the speciation of As(III) and As(V) in natural water samples with satisfactory results.     

Low pressure chromatographic separation of inorganic arsenic species using solid phase extraction cartridges

Routine water analysis of arsenic species requires simple, inexpensive, rapid and sensitive methods. To this end, we have developed two methods, which are based on the use of inexpensive solid phase extraction (SPE) cartridges as low pressure chromatographic columns for separation and hydride generation atomic absorption spectrometry (HGAAS) and hydride generation atomic fluorescence spectrometry (HGAFS) for detection of arsenic. Both anion exchange and reverse phase cartridges were successfully used to separate arsenite [As(III)] and arsenate [As(V)]. The composition, concentration, and pH of eluting buffers and the effect of flow rate were systematically investigated. Speciation of inorganic As(III) and As(V) were achieved within 1.5 min, with detection limits of 0.2 and 0.4 ng/ml, respectively. Both isocratic and step gradient elution techniques were suitable for the baseline resolution of As(III) and As(V) using anion exchange cartridges. Application of the methods to the speciation of As(III) and As(V) in untreated water, tap water, and bottled water samples were demonstrated. Results from the speciation of arsenic in a standard reference material water sample using these methods were in good agreement with the certified value and with inter-laboratory comparison results obtained using HPLC separation and inductively coupled plasma mass spectrometric detection (HPLC-ICPMS).     

Elimination of the chloride interference on the determination of arsenic using hydride generation inductively coupled plasma mass spectrometry.

In the determination of arsenic, attention has recently focused on the speciation of As(III) and As(V). Reversed-phase HPLC can be used to efficiently separate these two arsenic species. When inductively coupled plasma mass spectrometry is used for arsenic detection, an isobaric interference at m/z 75 is caused by the presence of chloride in the sample. These experiments describe the use of hydride generation in conjunction with a polypropylene-membrane gas-liquid separator to completely eliminate the transport of chloride to the plasma. A detection limit of 0.46 ppb for As(III) was achieved with this system. The chromatographic resolution of the system was not compromised by the addition of the gas-liquid separator. A determination of the arsenic content of a NIST urine sample was performed to demonstrate the effectiveness of the chloride elimination.     

Modified Activated Carbon as Solid Phase Extraction Adsorbent for the Preconcentration and Determination of Trace As(III) in Environmental Samples by Graphite Furnace Atomic Absorption Spectrometry

A simple and selective method was developed for the preconcentration, separation, and determination of trace amounts of As(III) in an aqueous solution by solid phase extraction combined with graphite furnace atomic absorption spectrometry. Activated carbon (AC) was modified by sodium diethyldithiocarbamate (NaDDTC) and then used as a new, stable and easily prepared solid sorbent in a mini column for the extraction of As(III) in aqueous solution. Factors influencing the sorption and desorption of As(III), such as volume and concentration of eluent, sample pH, flow rate and effect of interfering ions on the recovery of As(III) have been systemically investigated. At pH 2.0 As(III) could be adsorbed quantitatively by NaDDTC‐AC, and then eluted completely with 2 mL of 3.0 mol·L^?1 HNO₃. The amount of eluted As(III) was measured using graphite furnace atomic absorption spectrometry. The detection limit of As(III) was 0.04 ng·mL^?1 with enrichment factor of 100 and the relative standard deviation (RSD, n=8) was 1.58% at 10 ng·mL^?1 level.     

Simultaneous speciation of inorganic arsenic and antimony in water samples by hydride generation-double channel atomic fluorescence spectrometry with on-line solid-phase extraction using single-walled carbon nanotubes micro-column

A new method was developed for the simultaneous speciation of inorganic arsenic and antimony in water by on-line solid-phase extraction coupled with hydride generation-double channel atomic fluorescence spectrometry (HG-DC-AFS). The speciation scheme involved the on-line formation and retention of the ammonium pyrrolidine dithiocarbamate complexes of As(III) and Sb(III) on a single-walled carbon nanotubes packed micro-column, followed by on-line elution and simultaneous detection of As(III) and Sb(III) by HG-DC-AFS; the total As and total Sb were determined by the same protocol after As(V) and Sb(V) were reduced by thiourea, with As(V) and Sb(V) concentrations obtained by subtraction. Various experimental parameters affecting the on-line solid-phase extraction and determination of the analytes species have been investigated in detail. With 180 s preconcentration time, the enrichment factors were found to be 25.4 for As(III) and 24.6 for Sb(III), with the limits of detection (LODs) of 3.8 ng L^− 1 for As(III) and 2.1 ng L^− 1 for Sb(III). The precisions (RSD) for five replicate measurements of 0.5 μg L⁻¹ of As(III) and 0.2 μg L⁻¹ of Sb(III) were 4.2 and 4.8%, respectively. The developed method was validated by the analysis of standard reference materials (NIST SRM 1640a), and was applied to the speciation of inorganic As and Sb in natural water samples.     

Stability study of As(III), As(V), MMA and DMA by anion exchange chromatography and HG-AFS in wastewater samples

The stability of arsenic species (arsenate [As(V)], monomethylarsonate [MMA], dimethylarsinate [DMA] and arsenite [As(III)]) in two types of urban wastewater samples (raw and treated) was evaluated. Water samples containing a mixture of the different arsenic species were stored in the absence of light at three different temperatures: +4 degrees C, +20 degrees C and +40 degrees C. At regular time intervals, arsenic species were determined by high performance liquid chromatography (HPLC)-hydride generation (HG)-atomic fluorescence spectrometry (AFS). The experimental conditions for the separation of arsenic species by HPLC and their determination by AFS were directly optimised from wastewater samples. As(III), As(V), MMA and DMA were separated on an anion exchange column using phosphate buffer (pH 6.0) as the mobile phase. Under these conditions the four arsenic species were separated in less than 10 min. The detection limits were 0.6, 0.9, 0.9 and 1.8 micro g L(-1) for As(III), DMA, MMA and As(V), respectively. As(V), MMA and DMA were found stable in the two types of urban wastewater samples over the 4-month period at the three different temperatures tested, while the concentration of As(III) in raw wastewater sample decreased after 2 weeks of storage. A greater stability of As(III) was found in the treated urban wastewater sample. As(III) remained unaltered in this matrix at pH 7.27 over the period studied, while at lower pH (1.6) losses of As(III) were detected after 1 month of storage. The results show that the decrease in As(III) concentration with time was accompanied by an increase in As(V) concentration.     

Comparison of inorganic films and poly(4-vinylpyridine) coatings as electrode modifiers for flow-injection systems

A glassy-carbon electrode modified with a ruthenium-containing inorganic film was used for the flow-injection determination of As(III). The linear working range was 5-100 muM, and the detection limit was 300 pg. The response was reproducible for periods of several days. A glassy-carbon electrode modified by adsorption of a quaternized poly(4-vinylpyridine) film impregnated with hexachloroiridate(II and III) was used for the oxidation of nitrite. The calibration graphs were non-linear and varied from day to day, and the peak widths were broad. Nitrite determination at a platinum electrode modified by adsorption of iodine gave results analogous to the As(III) study; however, an overlayer of quaternized poly(4-vinylpyridine) decreased the sensitivity.     

The Use of Voltammetry for Sorption Studies of Arsenic (III) Ions by Magnetic Beads Functionalized with Nucleobase Hydrazide Derivatives

In this work the interaction characteristics of nucleobases with As(III) are studied. Novel materials consisting of magnetic nanoparticles (MNPs) functionalized with adenine hydrazide (AH), guanine hydrazide (GH) and uracil hydrazide (UH) were elaborated. The adsorption isotherms were investigated electrochemically and it was shown that the adsorption capacity of the nanoparticles towards arsenic (III) increased in the following order: AH<UH<GH. The electrochemical detection of As(III) using the GH functionalized MNPs offered better results compared with the other functionalizations, with a sensitivity of 1.92 μA μg⁻¹ L and a limit of detection of 1.6 μg/L (21 nM).     

Simultaneous determination of arsenic(III) and arsenic(V) by flow injection–inductively coupled plasma–atomic emission spectrometry (ICP-AES) with ultrasonic nebulization

A dual-column protocol for the sequential determination of As(III) and As(V) is described using inductively coupled plasma-atomic emission spectrometry (ICP-AES) with ultrasonic nebulization (USN). This procedure employed a 16-way valve containing two different homemade mini columns for selective preconcentration of As(III) and As(V). One column was filled with Muromac A-1, which selectively preconcentrated As(III) at pH 3 after complexation with ammonium pyrrolidine dithiocarbamate (APDC, 0.05%). The effluent of the first column was then passed through the second column, which was filled with an anion-exchange resin to collect As(V). By using 0.6 M sodium hydroxide, both species were eluted sequentially and measured by ICP-AES. Enrichment factors of 136 (17 for micro column x8 for USN) for As(V) and 160 (20 for micro column x8 for USN) for As(III) were achieved with 4 min preconcentration. With the proposed procedure, the detection limits were calculated to be 0.7 micro g L(-1) for As(V) and 0.8 micro g L(-1) for As(III) based on (3 sigma) blank determination ( N=10). The relative standard deviations for 20 micro g L(-1) of As(V) and As(III) were 5.8% and 6.5%, respectively. The recovery for spiked water samples was in the range of 85-112%.     

Voltammetric Determination of Arsenic with Modified Glassy Carbon Electrode

In this study, glassy carbon electrode modified with nano gold‐crystal violet film has been used to detect arsenite (As (III)) in a model system and in groundwater samples. The modified electrode was characterized by scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS). Using voltammetric measuring technique, linear response was obtained in a concentration range of 2.0–22.0 μM. The arsenite concentrations in groundwater samples varied between 2.4 μM to 4.8 μM. The sensitivity of the modified electrode for As (III) detection was 5.6 μA/μM cm² and 0.8 μM concentration was found as lower limit of detection (LOD). The accuracy of the method was checked with standard method anodic stripping voltammetry (ASV). Groundwater samples were characterized with dynamic (DLS) and electrophoretic (ELS) light scattering measurements which have shown that particles present in different samples differ in size distribution and zeta potential which did not interfere with As (III) detection.     

An Exfoliated Graphite Based Electrochemical Sensor for As(III) in Water

In this work, we present the application of an exfoliated graphite electrode modified with gold nanoparticles (AuNPs) for the detection of As(III) in acidic media. Gold nanoparticles were deposited on the surface of an exfoliated graphite electrode by electrodeposition at a potential window of ?0.2 V to 1.2 V. This was followed by activation in 0.5 M H₂SO₄ with 10 cycles from 0.6 V to 1.4 V. The modification of exfoliated graphite (EG) showed an increased electroactive surface area of the electrode and improved peak current output in a Fe(CN)₆^3?/4? redox probe. EG‐AuNPs electrode was used to detect As(III) in 1.0 M HNO₃ using square wave anodic stripping voltammetry (SWASV) technique at optimum conditions of pH 3, deposition potential of ?0.8 V, deposition time of 180 s, frequency of 5 Hz and pulse amplitude of 50 mV. The EG‐AuNPs electrode detected As(III) in solution to a limit of 0.58 ppb with regression of 0.9993. The method reported is simple, cheap and possesses good reproducibility. The developed electrochemical sensor was applied in the detection of As (III) in an industrial real water sample. The results of the real water sample analysis from the developed method are comparable with the inductively coupled plasma – optical emission spectroscopy (ICP‐OES) results.     

Speciation of very low amounts of arsenic and antimony in waters using dispersive liquid–liquid microextraction and electrothermal atomic absorption spectrometry

A new procedure for the determination of inorganic arsenic (III,V) and antimony (III,V) in water samples by dispersive liquid–liquid micro extraction separation and electrothermal atomic absorption spectrometry (ETAAS) is presented. At pH 1, As(III) and Sb(III) are complexed with ammonium pyrrolidine dithiocarbamate and extracted into the fine droplets formed when mixing carbon tetrachloride (extraction solvent), methanol (disperser solvent) and the sample solution. After extraction, the phases are separated by centrifugation, and As(III) and Sb(III) are determined in the organic phase. As(V) and Sb(V) remain in the aqueous layer. Total inorganic As and Sb are determined after the reduction of the pentavalent forms with sodium thiosulphate. As(V) and Sb(V) are calculated by difference. The detection limits are 0.01 and 0.05 µg L^− 1 for As(III) and Sb(III), respectively, with an enrichment factor of 115. The relative standard deviation is in the 2.9–4.5% range. The procedure has been applied to the speciation of inorganic As and Sb in bottled, tap and sea water samples with satisfactory results.