Overcoming matrix interferences in ion-exchange solid phase extraction of As, Cr, Mo, Sb, Se and V species from leachates of cement-based materials using multiple extractions

Solid phase extraction (SPE) methods based on multiple extractions have been developed to overcome matrix interferences in the charge-based fractionation analysis of As, Cr, Mo, Sb, Se and V leached from cement-based materials. Disposable SPE tubes packed with 500 mg strong anion-exchange (SAX) or strong cation-exchange (SCX) sorbents were used to extract the anionic and cationic species of the elements, respectively. The multiple extractions were based on the percolation of a small sample volume (5.0 mL) through a series of identical ion-exchange tubes. For most of the elements, more than 90% of the anionic species were extracted from a sample containing up to 16 g L⁻¹ NO₃⁻ by passing the aliquot through five identical SAX tubes. Percolating a sample aliquot through three identical SCX cartridges gave more than 99% retention for Cr(III) from leachates containing a high concentration of interfering metal cations. The anionic and cationic analytes showed only slight non-specific adsorption on the SCX and SAX sorbents, respectively, except for V(V) on the SCX sorbent. A condition was established for the quantitative elution of the retained analytes from the ion-exchange sorbents with 1.0 mol L⁻¹ HNO₃. The multiple ion-exchange SPE procedures were validated using spike recovery tests. The methods were used to determine the anionic and cationic fractions of the target elements in concrete leachates covering a broad range of pH (3.8-13.4). The elements were found to exist predominantly as anions in the alkaline and neutral leachates. A high fraction (85%) of cationic Cr was detected in the most acidic leachate (pH 3.8).     

Optimization of an anion-exchange high performance liquid chromatography-inductively coupled plasma-mass spectrometric method for the speciation analysis of oxyanion-forming metals and metalloids in leachates from cement-based materials

A method was developed for the speciation analysis of the oxyanions of As(III), As(V), Cr(VI), Mo(VI), Sb(III), Sb(V), Se(IV), Se(VI) and V(V) in leachates from cement-based materials, based on anion-exchange HPLC coupled with ICP-MS. The method was optimized in a two-step multivariate approach: the effect of sample pH and mobile phase composition on resolution, peak symmetry and analysis time was studied. Optimum conditions were then identified for the significant experimental factors by studying their interdependence. A mobile phase composition of 20 mM ammonium nitrate, 50 mM ammonium tartrate and pH 9.5 was found to be a compromise optimum for the separation of the target analytes using isocratic elution. The optimum condition provided separation of the analytes in less than 6 min, at a mobile phase flow rate of 1.0 mL/min. The signal intensities of the analytes were improved by adding 1% methanol to the mobile phase. The limit of detection of the method was in the range 0.2–2.2 μg/L for the various species. The effect of sample constituents was studied using spiked concrete leachates. The method was used to determine the target oxyanionic species in leachates generated from a concrete material in the pH range 3.5–12.4; CrO₄²⁻, MoO₄²⁻ and VO₄³⁻ were detected in most of the leachates.     

Multivariate optimization and simultaneous determination of hydride and non-hydride-forming elements in samples of a wide pH range using dual-mode sample introduction with plasma techniques: application on leachates from cement mortar material

Analytical methods have been developed for the simultaneous determination of hydride-forming (As, Sb) and non-hydride-forming (Cr, Mo, V) elements in aqueous samples of a wide pH range (pH 3–13). The methods used dual-mode (DM) sample introduction with ICP-AES and ICP-MS instruments. The effect of selected experimental variables, i.e., sample pH and concentrations of HNO₃, thiourea, and NaBH₄, were studied in a multivariate way using face-centered central composite design (FC-CCD). Compromised optimum values of the experimental parameters were identified using a response optimizer. The statistically found optimum values were verified experimentally. The methods provided improved sensitivities for the hydride-forming elements compared with the respective conventional nebulization (Neb) systems by factors of 67 (As) and 64 (Sb) for ICP-AES and 36 (As) and 54 (Sb) for ICP-MS. Slight sensitivity improvements were also observed for the non-hydride-forming elements. The limits of detection (LOD) of As and Sb were lowered, respectively, to 0.8 and 0.9 μg L⁻¹ with the DM-ICP-AES system and to 0.01 and 0.02 μg L⁻¹ with the DM-ICP-MS system. The short-term stabilities of both methods were between 2.1 and 5.4%. The methods were applied for the analysis of leachates of a cement mortar material prepared in the pH range 3–13. The elemental concentration of the leachates determined by the two DM methods were statistically compared with the values obtained from Neb-ICP-MS analysis; the values showed good agreement at the 95% confidence level. Quantitative spike recoveries were obtained for the analytes from most of the leachates using both DM methods. Figure Schematic of the dual-mode sample introduction system used in combination with ICP-AES and ICP-MS for the simultaneous determination of hydride and non-hydride-forming elements     

Simultaneous quantification of 17 trace elements in blood by dynamic reaction cell inductively coupled plasma mass spectrometry (DRC-ICP-MS) equipped with a high-efficiency sample introduction system

A quadrupole inductively coupled plasma mass spectrometer (Q-ICP-MS) equipped with a dynamic reaction cell (DRC) and coupled with a desolvating nebulization system (APEX-IR) was employed to determine 17 elements (Al, As, Ba, Cd, Co, Cr, Li, Mn, Mo, Ni, Pb, Sb, Se, Sn, Sr, V, and Zr) in blood samples. Ammonia (for Al, Cr, Mn, and V) and O₂ (for As and Se) were used as reacting gases. Selection of the best flow rate of the gases and optimization of the quadrupole dynamic bandpass tuning parameter (RPq) were carried out, using digested blood diluted 1 + 9 with deionized water and spiked with 1 μg L⁻¹ of Al, Cr, Mn, V and 5 μg L⁻¹ of As and Se. Detection limits were determined in digested blood using the 3σ criterion. The desolvating system allowed a sufficient sensitivity to be achieved to determine elements at levels of ng L⁻¹ without detriment of signal stability. The accuracy of the method was tested with the whole blood certified reference material (CRM), certified for Al, As, Cd, Co, Cr, Mn, Mo, Ni, Pb, Sb, Se, and V, and with indicative values for Ba, Li, Sn, Sr, and Zr. The addition calibration approach was chosen for analysis. In order to confirm the DRC data, samples were also analyzed by means of sector field inductively coupled plasma mass spectrometry (SF-ICP-MS), operating in medium (m/Δm = 4000) and high (m/Δm = 10,000) resolution mode and achieving a good agreement between the two techniques.     

Inorganic speciation of As(III, V), Se(IV, VI) and Sb(III, V) in natural water with GF-AAS using solid phase extraction technology

The paper presents a procedure for the multi-element inorganic speciation of As(III, V), Se(IV, VI) and Sb(III, V) in natural water with GF-AAS using solid phase extraction technology. Total As(III, V), Se(IV, VI) and Sb(III, V) were determined according to the following procedure: titanium dioxide (TiO₂) was used to adsorb inorganic species of As, Se and Sb in sample solution; after filtration, the solid phase was prepared to be slurry for determination. For As(III), Se(IV) and Sb(III), their inorganic species were coprecipitated with Pb-PDC, dissolved in dilute nitric acid, and then determined. The concentrations of As(V), Se(VI) and Sb(V) can be calculated by the difference of the concentrations obtained by the above determinations. For the determination of As(III), Se(IV) and Sb(III), palladium was chosen as a modifier and pyrolysis temperature was 800 °C. Optimum conditions for the coprecipitation were listed for 100 ml of sample solution: pH 3.0, 15 min of stirring time, 40.0 μg l⁻¹ Pb(NO₃)₂ and 150.0 μg l⁻¹ APDC. The proposed method was applied to the determination of trace amounts of As(III, V), Se(IV, VI) and Sb(III, V) in river water and seawater.     

A new and direct method for the trace element determination in cauliflower by differential pulse polarography

Using the DPP polarograms of wet digested cauliflower sample in acetate buffer at pH values of 2, 4 and 6, Fe, Zn, Mo, Se, Cr, Cd, Pb, Ti and Cu quantities were determined. The best separation and determination conditions for Zn, Se and Mo was pH 2; for Cr, Zn, Mo and As was pH 4; for Pb pH 6, for Ti, Cu and Fe was pH 6-7 EDTA, for Cd pH 2 EDTA and for lead pH 6, all in acetate buffer. The trace element ranges for cauliflowers from two different seasons were (first figure for winter, the second for summer) for Se 120-250 μg g⁻¹, Fe 70-85 μg g⁻¹, Cu 320-150 μg g⁻¹, Ti 90-120 μg g⁻¹, Cr 130-630 μg g⁻¹, Zn 90-550 μg g⁻¹, Mo 170-230 μg g⁻¹, Cd 20 μg g⁻¹ (in winter) and Pb 130-300 μg g⁻¹ in dry sample. Cd was under the detection limit in summer. The length of digestion time had no effect on the recovery of copper, iron, molybdenum and zinc between 15 and 3 h of digestion.     

Determination of metals and metalloids in light and heavy crude oil by ICP-MS after digestion by microwave-induced combustion

A method for light and heavy crude oil digestion using microwave-induced combustion (MIC) in closed vessels is described for further determination of Ag, As, Ba, Bi, Ca, Cd, Cr, Fe, K, Mg, Li, Mn, Mo, Ni, Pb, Rb, Se, Sr, Tl, V, and Zn by inductively coupled plasma mass spectrometry (ICP-MS). Conventional microwave-assisted acid digestion (MW-AD) in pressurized vessels and analyte determination by inductively coupled plasma optical emission spectrometry (ICP OES) were also used for results comparison. For MIC procedure, samples were wrapped in polyethylene films and combusted using 20 bar of oxygen and 50 µl of 6 mol l^− 1 ammonium nitrate as aid for ignition. The concentration of nitric acid used as absorbing solution was evaluated (1, 2, 4, 7, 10 and 14 mol l^− 1) using an additional reflux step after combustion. Accuracy was evaluated for As, Ba, Ni, Se V, and Zn using certified reference material (CRM) with similar matrix composition and for Cr, Fe, K, Mg, Mn, and Mo by neutron activation analysis (NAA). Recovery tests were also performed for all the analytes by MIC and they were better than 97% using 2 mol l^− 1 nitric acid as absorbing solution (with reflux step). Agreement with certified values and NAA results was better than 95%. Using MIC it was possible to obtain lower limits of detection (LODs) by ICP-MS and also by ICP OES in comparison with those obtained by MW-AD. In spite of both sample preparation techniques were apparently suitable for crude oil digestion, MIC was preferable in view of the possibility of using diluted nitric acid as absorbing solution that is an important aspect to minimize interferences by ICP-MS and ICP OES. In order to avoid polyatomic interferences on ⁵²Cr and ⁵⁶Fe determinations by ICP-MS, a dynamic reaction cell with ammonia gas was used. Residual carbon content in digests obtained by MW-AD and MIC was 15% and < 1%, respectively. Using MIC the simultaneous digestion of 8 samples was possible in less than 30 min.     

Determination of Mn,Co, Cu,Zn, Ag,Bi, Cd,Se, Cr and Te in anatolian iron artifacts by instrumental neutron activation analysis and atomic absorption spectrophotometry

Two methods of concentration of Ag, As, Cd, Co, Cr, Cu, Fe, Hg, In, Mo, Mn, Sb, Sc, Se, W and Zn from water have been elaborated. The trace elements are preconcentrated by coprecipitation with thionalide at pH 9, 1 and 0 or by sorption on ion exchange resin Dowex 1×2 loaded with 8-hydroxyquinoline-5-sulfonic acid at pH 7.     

Simultaneous multi-element analysis of total As, Se and Sb on titanium dioxide by slurry sampling-graphite furnace atomic absorption spectrometry

A simple and rapid method for simultaneous determination of As, Se and Sb was studied by graphite furnace atomic absorption spectrometry (GFAAS). Titanium dioxide adsorbing As, Se and Sb was separated from sample solution (100 ml) with a membrane filtration (0.45 μm), and then prepared to be slurry (5.0 ml) by adding ultrapure water. The behavior and influence of titanium dioxide on determination of As, Se and Sb were investigated in this experiment. The optimal conditions of a furnace for these elements were chosen as follows: pyrolysis temperature was 150 °C, and atomization temperature was 2300 °C. The optimal conditions of adsorption for As, Se and Sb on titanium dioxide were listed: pH 2.0 in sample solution; 10 min of stirring time; and 20.0 mg titanium dioxide. The difference of the chemical valence of each element had no effect on the recovery of each element at the same optimal conditions. Limits of detection (3σ) for As, Se and Sb were found to be 0.21 μg l⁻¹, 0.15 μg l⁻¹ and 0.15 μg l⁻¹, respectively, with enrichment rate of 20, when 20 μl of slurry was injected into a Zr-coating tube. The proposed method was applied to tap water and river water.     

An evaluation of ferrihydrite- and Metsorb™-DGT techniques for measuring oxyanion species (As,Se, V,P): Effective capacity,competition and diffusion coefficients

This study investigated several knowledge gaps with respect to the diffusive gradients in thin films (DGT) technique for measurement of oxyanions (As(III), As(V), Se(IV), Se(VI), PO₄³⁻, and V(V)) using the ferrihydrite and Metsorb™ binding layers. Elution efficiencies for each binding layer were higher with 1:20 dilutions, as analytical interferences for ICP-MS were minimised. Diffusion coefficients measured by diffusion cell and by DGT time-series experiments were found to agree well and generally agreed with previously reported values, although a range of diffusion coefficients have been reported for inorganic As and Se species. The relative binding affinity for both ferrihydrite and Metsorb™ was PO₄³⁻ ≈ As(V) > V(V) ≈ As(III) > Se(IV) ? Se(VI) and effective binding capacities were measured in single ion solutions, and spiked synthetic freshwater and seawater, advising practical decisions about DGT monitoring. Under the conditions tested the performance of both ferrihydrite and Metsorb™ binding layers was directly comparable for As(V), As(III) Se(IV), V(V) and PO₄³⁻ over a deployment spanning ≤2 days for both freshwater and seawater. In order to return quantitative data for several analytes we recommend that the DGT method using either ferrihydrite or Metsorb™ be deployed for a maximum of 2 days in marine waters likely to contain high levels of the most strongly adsorbing oxyanions contaminants. The high pH, the competitive ions present in seawater and the identity of co-adsorbing ions affect the capacity of each binding layer for the analytes of interest. In freshwaters, longer deployment times can be considered but the concentration and identity of co-adsorbing ions may impact on quantitative uptake of Se(IV). This study found ferrihydrite-DGT outperformed Metsorb-DGT while previous studies have found the opposite, with variation in binding materials masses used being a likely reason. Clearly, preparation of both binding layers should always be optimised to produce the highest capacity possible, especially for seawater deployments.     

Evaluation of a tungsten coil atomization-laser-induced fluorescence detection approach for trace elemental analysis

The analytical utility of a tungsten (W)-coil atomization-laser-induced fluorescence (LIF) approach has been evaluated for trace level measurements of elemental chromium (Cr), arsenic (As), selenium (Se), antimony (Sb), lead (Pb), tin (Sn), copper (Cu), thallium (Tl), indium (In), cadmium (Cd), zinc (Zn) and mercury (Hg). Measurements of As, Cr, In, Se, Sb, Pb, Tl, and Sn were performed by laser-induced fluorescence using a single dye laser operating near 460 nm whose output was converted by frequency doubling and stimulated Raman scattering to wavelengths ranging from 196 to 286 nm for atomic excitation. Absolute limits of detection (LODs) of 1, 0.3, 0.3, 0.2, 1, 6, 1, 0.2 and 0.8 pg and concentration LODs of 100, 30, 30, 20, 100, 600, 100, 20, and 80 pg/mL were achieved for As, Se, Sb, Sn, In, Cu, Cr, Pb and Tl, respectively. Determinations of Hg, Pb, Zn and Cd were performed using two-color excitation approaches and resulted in absolute LODs of 2, 30, 5 and 0.6 pg, respectively, and concentration LODs of 200, 3000, 500 and 60 pg/mL, respectively. The sensitivities achieved by the W-coil LIF approaches compare well with those reported by W-coil atomic absorption spectrometry, graphite furnace atomic absorption spectrometry, and graphite furnace electrothermal atomization-LIF approaches. The accuracy of the approach was verified through the analysis of a multielement reference solution containing Sb, Pb and Tl which each had certified performance acceptance limits of 19.6-20.4 μg/mL. The determined concentrations were 20.05 ± 2.60, 20.70 ± 2.27 and 20.60 ± 2.46 μg/mL, for Sb, Pb and Tl, respectively. The results demonstrate that W-coil LIF provides good analytical performance for trace analyses due to its high sensitivity, linearity, and capability to measure multiple elements using a single tunable laser and suggest that the development of portable W-coil LIF instrumentation using compact, solid-state lasers is feasible.     

Characterization of estuarine sediments by near infrared diffuse reflectance spectroscopy

It has been developed a partial least squares near infrared (PLS-NIR) method for the determination of estuarine sediment physicochemical parameters. The method was based on the chemometric treatment of first order derivative reflectance spectra obtained from samples previously lyophilized and sieved through a lower than 63 μm grid. Spectra were scanned from 833 to 2976 nm, averaging 36 scans per spectrum at a resolution of 8 cm⁻¹, using chromatographic glass vials of 9.5 mm internal diameter as measurement cells. Models were built using reference data of 31 samples selected through the use of a hierarchical cluster analysis of NIR spectra of sediments obtained from the Ria de Arousa estuary and prediction parameters were established from a validation set of 50 samples of the same area. pH, redox potential (Eh), carbon (C), nitrogen (N) and hydrogen (H) content together with Sn, Pb, Cd, As, Sb and total Cr and also acid soluble, reducible and oxidable Cr fractions were employed as characteristic parameters of the studied sediments. Standard error of prediction values for C and N content were of the order of 4 and 1.3 mg g⁻¹ for H. Prediction errors for pH and Eh were 0.15 units and 37 mV, respectively, thus indicating the good prediction capabilities of the method. Regarding trace metal concentrations PLS-NIR provided prediction error levels for unknown samples around 20% for Sn, Pb, As and Sb and root mean square errors of prediction around 40% for concentration levels of 400 ng g⁻¹ Cd and 100 μg g⁻¹ Cr. For the different extractable fractions of Cr the residual prediction deviation varied from 1.3 to 1.7 but relative errors found for samples of the validation set were only useful for screening purposes.     

Detoxification of antimony by selenium and their interaction in paddy rice under hydroponic conditions

Antimony (Sb) contamination has become a growing concern in recent years. Strategies for reducing Sb contamination and its related health risks are urgently desired. This study was conducted to explore the possibility of selenium (Se) detoxification on Sb toxicity in paddy rice in order to find a feasible method to reduce the health risk of Sb pollution. Seedlings of paddy rice were exposed to 5 mg L⁻¹ Sb (KSbC₄H₄ O₇·1/2H₂O), in the presence of Se (Na₂SeO₃) at 0.1, 1, 5 mg L⁻¹ in culture solution, with no Sb and Se addition as the control. Paddy rice took up Sb greatly and the highest Sb contents measured among all treatments in this experiment in the leaves, stems and roots were 65.5, 298.5 and 195.7 mg kg⁻¹, respectively. Without Sb addition in the solution, single exposure to 0.1 mg L⁻¹ Se remarkably reduced the malondialdehyde (MDA) formation in paddy rice,demonstrating the beneficial effect of Se at low dosages. The addition of 5 mg L⁻¹ Sb was found to generate toxicity to paddy rice, showing as decreased biomass and increased leaf MDA content in paddy rice, while addition of 1 mg L⁻¹ Se mitigated the toxicity of Sb, as seen with the decreased leaf MDA content and increased biomass, indicating antidotal role of Se to Sb. In addition, the presence of 0.1, 1, 5 mg L⁻¹ Se generally decreased the accumulation of Sb in the leaves, stems and roots in paddy rice. Toxicity was also seen when paddy rice was exposed to single Se at 1 and 5 mg L⁻¹ levels, however, 5 mg L⁻¹ Sb addition was found to decrease the contents of Se in the leaves/stems whereas increased them in roots, accompanied with decreased MDA contents and increased biomass in paddy rice, indicating a possible detoxification role of Sb to Se too. Therefore, Sb, although toxic, could also be an antitoxin to Se in paddy rice at certain condition. Our results showed that Se could alleviate Sb toxicity efficiently in paddy rice through two effects as antagonism and antioxidation.     

Analysis of interferents by means a D-optimal screening design and calibration using partial least squares regression in the spectrophotometric determination of Cr(VI)

Using a central composite design, the signal of the process for the spectrophotometric determination of hexavalent chromium (λ = 543 nm) is maximised and its variability minimised using as complexing agent 1,5-diphenylcarbazide in sufficiently acid medium. To analyse the interference of various analytes (Mo(VI), V(V), Fe(III) and Mn(VII)) on the Cr(VI) as a function of concentration of interferent, a factorial design was prepared at three levels of each (zero, medium and high concentration), which implies performing 81 determinations. However, a D-optimal design with just nine experiments is sufficiently good to estimate the model proposed.The interference of these metals makes it impossible to determine Cr(VI) when they are present in the sample. To avoid prior separation steps, a multivariate regression by partial least squares, PLS, is proposed to calibrate the Cr(VI) in the presence of these analytes varying the concentration of the Cr(VI) between 0.1 and 0.9 μg ml⁻¹ and that of the interferents between 3 and 5 μg ml⁻¹. The average errors obtained were 4.5% and 3.29% fitted and in prediction, respectively, with a standard error in prediction (RMSEP) of 0.016% presenting absence of both constant and proportional bias.The detection limit with the PLS regression in the presence of interferents is 0.1 μg ml⁻¹ with a probability of false positive equal to 5% and less than 5% for false negative. The capability of detection is similar to that obtained with the univariate calibration (absorbance at 543 nm) in absence of interferents.With the PLS regression it is possible to discriminate 0.085 μg ml⁻¹ of Cr(VI) in a sample with 0.5 μg ml⁻¹ of Cr(VI) with probabilities of false compliance and false non-compliance equal to 0.05. For the univariate calibration without interferents, it was established at 0.0971 μg ml⁻¹ of Cr(VI) for the same nominal concentration.In relation to interference of V(V), Fe(III) and Mn(VII), the PLS calibration could be an efficient alternative to the separation step for Cr(VI) spectrophotometric determination using 1,5-diphenylcarbazide.     

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.     

Liquid chromatography-hydride generation-atomic fluorescence spectrometry hybridation for antimony speciation in environmental samples

Atomic fluorescence spectrometry was used as an element-specific detector in hybridation with liquid chromatography (LC) and hydride generation for the speciation of Sb(III), Sb(V) and trimethylantimony dichloride (TMSbCl₂). The three species were poorly resolved in a single chromatogram but good results were obtained by anion-exchange chromatography, using a mobile phase with 20 mM EDTA and 8 mM hydrogenphthalate to separate Sb(III) and Sb(V) and 1 mM carbonate at pH 10 to separate Sb(V) and TMSbCl₂. Calibration graphs were linear between 2 and 100 μg l⁻¹. Detection limits were 0.9, 0.5 and 0.7 μg l⁻¹ for Sb(III), Sb(V) and TMSbCl₂, respectively. The method was applied to the speciation of antimony in environmental samples.     

Determination of arsenic and antimony in seawater by voltammetric and chronopotentiometric stripping using a vibrated gold microwire electrode

The oxidation potentials of As⁰/As^III and Sb⁰/Sb^III on the gold electrode are very close to each other due to their similar chemistry. Arsenic concentration in seawater is low (10–20 nM), Sb occurring at ∼0.1 time that of As. Methods are shown here for the electroanalytical speciation of inorganic arsenic and inorganic antimony in seawater using a solid gold microwire electrode. Anodic stripping voltammetry (ASV) and chronopotentiometry (ASC) are used at pH ≤ 2 and pH 8, using a vibrating gold microwire electrode. Under vibrations, the diffusion layer size at a 5 μm diameter wire is 0.7 μm. The detection limits for the As^III and Sb^III are below 0.1 nM using 2 min and 10 min deposition times respectively. As^III and Sb^III can be determined in acidic conditions (after addition of hydrazine) or at neutral pH. In the latter case, oxidation of As⁰ to As^III was found to proceed through a transient As^III species. Adsorption of this species on the gold electrode at potentials where Sb^III diffused away is used for selective deposition of As^III. Addition of EDTA removes the interfering effect of manganese when analysing As^III. Imposition of a desorption step for Sb^III analysis is required. Total inorganic arsenic (iAs = As^V + As^III) can be determined without interference from Sb nor mono-methyl arsenious acid (MMA) at 1.6 < pH < 2 using E_dep = −1 V. Total inorganic antimony (iSb = Sb^V + Sb^III) is determined at pH 1 using E_dep = −1.8 V without interference by As.     

Synthesis of chitosan resin possessing 3,4-diamino benzoic acid moiety for the collection/concentration of arsenic and selenium in water samples and their measurement by inductively coupled plasma-mass spectrometry

A chitosan resin functionalized with 3,4-diamino benzoic acid (CCTS-DBA resin) was newly synthesized by using a cross-linked chitosan (CCTS) as base material. The adsorption behavior of trace amounts of elements on the CCTS-DBA resin was examined by the pretreatment with a mini-column and measurement of the elements by inductively coupled plasma-Mass spectrometry (ICP-MS). Arsenic(V) could be retained on the CCTS-DBA resin at pH 3 as an oxoanion of H₂AsO₄⁻. Selenium(VI) is strongly adsorbed at pH 2 and pH 3 as an oxoanion of SeO₄²⁻, while selenium(IV) as HSeO₃⁻ is adsorbed on the resin at pH 3. The sorption capacities are 82, 64, and 88 mg g⁻¹resin for As(V), Se(IV), and Se(VI), respectively. The effect of common anions and cations on the adsorption of As(V), Se(IV), and Se(VI) were studied; there was no interference from such anionic matrices as chloride, sulfate, phosphate, and nitrate up to 20 ppm, as well as from such artificial river water matrices as Na, K, Mg, and Ca after passing samples through the mini-column containing the resin. The CCTS-DBA resin was applied to the collection of arsenic and selenium species in bottled drinking water, tap water, and river water.     

Speciation of selenium(IV) and selenium(VI) in environmental samples by the combination of graphite furnace atomic absorption spectrometric determination and solid phase extraction on Diaion HP-2MG

A simple solid phase extraction procedure for speciation of selenium(IV) and selenium(VI) in environmental samples has been proposed prior to graphite furnace atomic absorption spectrometry. The method is based on the solid phase extraction of the selenium(IV)-ammonium pyrrolidine dithiocarbamate (APDC) chelate on the Diaion HP-2MG. After reduction of Se(VI) by heating the samples in the microwave oven with 4 mol l⁻¹ HCl, the system was applied to the total selenium. Se(VI) was calculated as the difference between the total selenium content and Se(IV) content. The experimental parameters, pH, amounts of reagents, eluent type and sample volume were optimized. The recoveries of analytes were found greater than 95%. No appreciable matrix effects were observed. The adsorption capacity of sorbent was 5.20 mg g⁻¹ Se (IV). The detection limit of Se (IV) (3sigma, n = 11) is 0.010 μg l⁻¹. The preconcentration factor for the presented system was 100. The proposed method was applied to the speciation of selenium(IV), selenium(VI) and determination of total selenium in natural waters and microwave digested soil, garlic, onion, rice, wheat and hazelnut samples harvested various locations in Turkey with satisfactory results. In order to verify the accuracy of the method, certified reference materials (NIST SRM 2711 Montana Soil, NIST SRM 1568a Rice Flour and NIST SRM 8418 Wheat Gluten) were analyzed and the results obtained were in good agreement with the certified values. The relative errors and relative standard deviations were below 6 and 10%, respectively.