Sorption behavior of selenide on montmorillonite

Batch sorption experiments were performed to investigate the sorption mechanism of Se on montmorillonite under reducing conditions in deep geological environments. Based on E_h–pH diagrams and ultraviolet–visible spectra, Se was dissolved as selenide (Se(–II)) anions under the experimental conditions. The distribution coefficients (K_d; m³ kg^?1) of Se(–II) indicated ionic strength independence and slight pH dependence. The K_d values of Se(–II) were higher than those of Se(IV), which also exists as an anionic species. X-ray absorption near edge spectroscopy showed that the oxidation state of Se-sorbed on montmorillonite was zero even though selenide remained in the solution. These results suggest that Se(–II) was oxidized and precipitated on the montmorillonite surface. Therefore, it is implied that a redox reaction on the montmorillonite surface contributed to high K_d values for Se(–II).

     

Study of the lipophilicity of selenium species

In this work the lipophilicity of different selenium species occurring in environmental matrices and food, Se(IV), Se(VI), selenomethionine (Se-Met), selenocystamine (Se-CM), selenocystine (Se-Cyst), and dimethyl diselenide (CH₃)₂Se₂, was investigated in the octanol–water system, using the shaking flask method and detection with inductively coupled plasma–atomic emission spectrometry (ICP–AES), in order to assess their environmental fate and tendency to bioaccumulate. Polarography was also used for the electrochemically active Se species, Se(IV), Se-Cyst, Se-CM and (CH₃)₂Se₂, and the results were compared with those measured by ICP–AES. Furthermore, the influence of pH was studied by determining the logarithm of the distribution coefficient, log D, at three pH values, 5, 7, and 9, as was the impact of the marine environment on the lipophilicity profile of the six investigated Se species. The results were compared with those estimated approximately by use of PrologD software, based on the Ghose-Crippen log P (P: partition coefficient) calculation system, the only system which incorporates values—even though approximate—for the atom type of Se. Finally, from our experimental data an indicative value of the Se–Se fragment for log P prediction, for use in drug design, was estimated.     

Stability of selenium and its speciation analysis in water using automatic system separation and HR-ICP-MS measurement

A simple and convenient method has been developed for the pre-concentration and separation of inorganic selenium species from environmental water samples using anion exchange chromatographic column combined with high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) measurement. ⁷⁵Se(IV) and ⁷⁵Se(VI) were prepared and used as tracers during the experiments. The volatility of selenium during solution evaporation was investigated to establish a reliable water samples pretreatment procedure. The parameters which affect the uptake of Se(IV) and Se(VI) on Dowex1 × 8 resin was optimized and the procedure for Se(IV) and Se(VI) separation was proposed. Both Se(IV) and Se(VI) are retained on the column in natural or alkaline solution with high distribution coefficient. The successive gradient elution of pre-concentrated species of selenium with HNO₃ solution allows to differentiate between them. Se(IV) and Se(VI) finally were eluted with 0.05 mol/L HNO₃ and 5.0 mol/L HNO₃, respectively. The proposed method has been successfully verified using the certified reference materials (CRMs) of real water samples, and spiked recoveries for real samples were 98%-104% with 5% relative standard deviations (RSDs). The developed procedure is proved to be reliable and can be used for the rapid determination of selenium species in environmental water samples.     

Simultaneous speciation of arsenic (As(III), MMA, DMA, and As(V)) and selenium (Se(IV), Se(VI), and SeCN−) in petroleum refinery aqueous streams

High-performance liquid chromatography (HPLC) coupled to an ICP-MS with an octapole reaction system (ORS) has been used to carry out quantitative speciation of selenium (Se) and arsenic (As) in the stream waters of a refining process. The argon dimers interfering with the ⁷⁸Se and ⁸⁰Se isotopes were suppressed by pressurizing the octapole chamber with 3.1 mL min⁻¹ H₂ and 0.5 mL min⁻¹ He. Four arsenic species arsenite—As(III), arsenate (As(V)), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA)—and three inorganic Se species—selenite Se(IV), selenate Se(VI), and selenocyanate (SeCN⁻)—were separated in a single run by ion chromatography (IC) using gradient elution with 100 mmol L⁻¹ NH₄NO₃, pH 8.5, adjusted by addition of NH₃, as eluent. Repeatabilities of peak position and of peak area evaluation were better than 1% and about 3%, respectively. Detection limits (as 3σ of the baseline noise) were 81, 56, and 75 ng L⁻¹ for Se(IV), Se(VI), and SeCN⁻, respectively, and 22, 19, 25, and 16 ng L⁻¹ for As(III), As(V), MMA, and DMA, respectively. Calibration curve R ² values ranged between 0.996 and 0.999 for the arsenic and selenium species. Column recovery for ion chromatography was calculated to be 97 ± 6% for combined arsenic species and 98 ± 3% for combined selenium species. Because certified reference materials for As and Se speciation studies are still not commercially available, in order to check accuracy and precision the method was applied to certified reference materials, BCR 714, BCR 1714, and BCR 715 and to two different refinery samples—inlet and outlet wastewater. The method was successfully used to study the quantitative speciation of selenium and arsenic in petroleum refinery wastewaters.     

Polarographic Studies on Se(IV) in Absence and Presence of Pb(II), Zn(II) and Sb(III) Ions in Aqueous N-(2-ACETAMIDO) Imino Diacetate Buffer Solutions

Abstract

The polarographic reduction and determination of selenite ions in absence and presence of a mixture of some cationic species such as, Pb(II), Zn(II) and Sb(III) in N-(2-acetamido) imino diacetate solutions, at constants of ionic strength 0.1 mol dm^?3 (KNO₃) and temperature 25°C was studied using direct current and differential pulse polarographic (DPP) techniques. It was shown that reduction of Se(IV) takes place along one, two or three waves depending on the pH value of the solution using the direct current polarographic measurements. The reduction of Se(IV) in N-(2-acetamido) imino diacetate buffer solutions was found to be reversible and involving six electron transfer process. Microcoulometric experiments was performed at the limiting current region of the different waves and at various pH values. Kinetic parameters and wave characteristics for the reduction of selenite ions have been calculated. A method for the analytical determination of selenite ions in either simple or quadruple mixture of ADA buffer solutions using DPP techniques are reported and discussed.     

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.     

On line speciation of Se(VI), Se(IV), and trimethylselenium by HPLC-microwave oven-hydride generation-atomic absorption spectrometry

An on-line system is proposed consisting of an anion-exchange chromatographic column, microwave-induced thermooxidation of trimethylselenium in the presence of persulphate, and microwave-induced thermoreduction of Se(VI) to Se(IV) in HCl medium, followed by hydride generation and atomic absorption for the determination of trimethylselenium (TMeSe), Se(IV) and Se(VI). Trimethylselenium is eluted in the dead volume of an anion-exchange column (Hamilton PRP-X-100), before elution of Se(IV) and Se(VI). Optimum chromatographic conditions have been obtained using 100 mmol L^–1 phosphate buffer (pH=6.8) H₂PO ₄ ^– /HPO ₄ ^2– as the mobile phase. Recoveries were around 100%, absolute detection limits were 1.1, 1.4 and 2.2 ng for TMeSe, Se(IV) and Se(VI), respectively. Precision was lower than 10% in all cases. The method has been applied to tap 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.     

Sorption of selenite onto chlorite considering mineral dissolution

In this study we investigated the sorption of selenite (SeO₃ ^2?) onto chlorite as a function of Se(IV) concentration, pH, and ionic strength. The sorption isotherm of Se(IV) onto chlorite was successfully presented by both the Langmuir isotherm and Tempkin equation although the Langmuir isotherm is somewhat better than the Tempkin equation. The sorption of Se(IV) onto chlorite was maintained to be constant at an acidic pH region, while the sorption decreased with an increasing pH at neutral and alkaline pH regions. However, the Se(IV) sorption onto chlorite was independent of the ionic strength of NaClO₄ solution. The amount of Se(IV) sorbed onto chlorite was significantly low compared to those of iron oxides such as apatite, goethite, hematite, and magnetite because of the lower content of Fe. We also investigated the effect of Fe(II) ions dissolved from chlorite on the Se(IV) sorption as a function of contact time. The chemical oxidation states of selenium sorbed onto chlorite surface were identified using X-ray absorption near edge structure (XANES) at the Pohang synchrotron light source. The amount of Fe(II) dissolved was increased by the contact time of 28 days but decreased after 28–56 days although the amount of dissolved Fe(II) ions was significantly small. This decrease of the dissolved Fe(II) may be due to the formation of Fe-oxyhydroxides such as ferrihydrite. The results of XANES measurements also showed that the Se(IV) sorbed onto chlorite was not reduced into Se(0) or Se(-II) even in the presence of Fe(II) ions in the solution because of the low Fe content of the chlorite although the mechanism was not clearly understood.     

Role of solution chemistry on the trapping of radionuclide Th(IV) using titanate nanotubes as an efficient adsorbent

Titanate nanotubes (TNTs) have attracted great interest in multidisciplinary study since their discovery. The adsorption of thorium [Th(IV)] onto TNTs in the absence and presence of humic acid (HA)/fulvic acid (FA) was studied by batch technique. The influence of pH from 2.0 to 10.0, ionic strength from 0.001 to 0.1 mol L^?1 NaClO₄, and coexisting electrolyte cations (Li⁺, Na⁺, K⁺) and antions (ClO₄ ^?, NO₃ ^?, Cl^?) on the adsorption of Th(IV) onto TNTs was tested. The adsorption isotherms of Th(IV) was determined at pH 3.0 and analyzed with Langmuir and Freundlich adsorption models, respectively. The results demonstrated that the adsorption of Th(IV) onto TNTs increases steeply with increasing pH from 2.0 to 4.0. Generally, HA/FA was showed to enhance Th(IV) adsorption onto TNTs at low pH values, but to reduce Th(IV) adsorption onto TNTs at high pH values. The adsorption of Th(IV) onto TNTs was also dependent on coexisting electrolyte ions in aqueous solution under our experimental conditions. The adsorption of Th(IV) onto TNTs is exothermic and spontaneous. The findings indicating that TNTs can be used as a promising candidate for the enrichment and solidification of Th(IV) or its analogue actinides from large volume solution in real work.     

Separation and preconcentration of Se(IV)/Se(VI) speciation on algae and determination by graphite furnace atomic absorption spectrometry in sediment and water

A novel method for the separation and preconcentration of Se(IV)/ Se(VI) with algae and determination by graphite furnace atomic absorption spectrometry (GFAAS) has been developed. The Se(VI) is extracted with algae from the solution containing Se(IV)/Se(VI) at pH 5.0, and the remaining Se(IV) is then preconcentrated pH 1.0. The detection limits (3σ, n = 11) of 0.16 μg L^–1 for Se(IV) and 0.14 μg L^–1 for Se(VI) are obtained using 40 mL of solution. At the 2.0 μg L^–1 level the relative standard deviation is 2.6% for Se(IV) and 2.3% for Se(VI). The method has been applied to the determination of Se(IV)/Se(VI) in sediment and water samples. Analytical recoveries of Se(IV) and Se(VI) added to samples are ?97 ± 5% and 102 ± 6% (95% confidence), respectively. Received: 10 February 1999 / Revised: 21 June 1999 / /Accepted: 22 June 1999     

Determination and speciation of selenium in water samples collected from Muğla (Turkey) province by hydride generation atomic absorption spectrometry

In this work, determination of selenium in various water samples was done by using hydride generation atomic absorption spectrometry. The most appropriate values of HCl concentration, NaBH₄ concentration, NaOH concentration, flow rate of argon and flow rate of waste solution were determined. The optimum concentration of the HCl, NaBH₄ and NaOH solutions were found to be 7.0 mol L^?1, 1.0% and 0.75%, respectively. The optimum flow rate of Ar gas and waste solution were also found to be 100.9 mL min^?1 and 4.0 mL min^?1, respectively. Values of LOD and LOQ were calculated separately for total Se and Se(IV). LOD and LOQ values were calculated 0.56 μg L^?1, 1.87 μg L^?1 for total Se and 0.72 μg L^?1, 2.40 μg L^?1 for Se(IV), respectively. The precision was evaluated by relative standard deviation (RSD%) was found to be 3.5% for total Se and 3.1% for Se(IV) (n = 11). A standard reference material (NIST 1643e) was used in order to check the accuracy of the proposed method. There was a good agreement between certified and found values for standard reference material. The method was applied to the analysis of total Se and Se(IV) concentrations in tap water samples collected from the various regions of Mu?la. Proposed method showed spike recovery ranges from 92% to 116% in water samples.     

DNA Binding Studies and Evaluation of Electrochemical Parameters of New Tri-and Di-Organotin(IV) Complexes of 4-(1H-Indol-3-yl)butanoic Acid

New triorganotin(IV) [R₃SnL where R = Me (1), Bu (2), Ph (3)] and diorganotin(IV) [R₂SnL₂, where R = Me (4), Bu (5), Ph (6)] derivatives of 4-(1H-indol-3-yl)butanoic acid (HL) were prepared and characterized by FT-IR and ¹H and ¹³C NMR spectroscopy. Interaction between DNA and selected compounds was studied by UV-Vis spectroscopy and viscometry. The binding constants calculated on the basis of the accumulated data reveal the following order of binding strength: compound 2 > 1 > 5 > 4. Electrochemical parameters such as diffusion coefficient and charge transfer coefficient are evaluated with cyclic voltammetry. The results demonstrate that diorganotin(IV) complexes are characterized by higher diffusion coefficient than triorganotin(IV) analogues. In case of triorganotin(IV) complexes, the lower coordination number allows a solvent to interact with Sn(IV) center and hence decreases the rate of diffusion.

     

Improving the efficiency in the detection of gamma activities in environmental soil samples: influence of the granulometry and soil density

Ti(OH)₄ and TiCl₄ modified bentonite (Ti–Na-bent) were applied in the removal of Th(IV) from aqueous solution. Effect of different factors such as pH, contact time, temperature, initial concentration of Th(IV) and efficiency of them for thorium adsorption are investigated. Ti–Na-bent showed high adsorption capacity (q_m?=?231.37 mg/g) and quick adsorption kinetics at lower pH. The adsorption mechanisms involved are: (1) Th⁴⁺, [Th(OH)_4?n]ⁿ⁺ complexed on the outer-sphere of Na-bent and Ti–Na-bent. (2) Ion exchange between Th⁴⁺, [Th(OH)_4?n]ⁿ⁺ and exchangeable cations of Na-bent and the H on the hydroxyl group of Ti(OH)₄. Ti–Na-bent manifested high adsorption capacity for Th(IV), good acid resistance and long-term adsorption stability.

     

Solubility of Eu<Subscript>2</Subscript>(SeO<Subscript>3</Subscript>)<Subscript>3</Subscript> and sorption of Eu(III) onto TiO<Subscript>2</Subscript> in the presence of Se(IV)

Metal ions sorption can be significantly affected by the presence of other sorbates, especially of complexing ligands. In this study, the effect of Se(IV) on Eu(III) sorption onto TiO₂ at different pH and Eu(III) concentration was investigated. Se(IV) was found to enhance Eu(III) sorption as a function of Se(IV) concentration. Constant capacitance model was successfully used to interpret the sorption experimental data. The solubility product of Eu₂(SeO₃)₃ at ambient temperature was investigated to highlight the sorption mechanism of ternary sorption system. The pK _sp value of Eu₂(SeO₃)₃ was found to be 31.51 ± 0.95.     

Comparison of ultrasound-assisted emulsification and dispersive liquid–liquid microextraction methods for the speciation of inorganic selenium in environmental water samples using low density extraction solvents

Herein, ultrasound-assisted emulsification microextraction (USAEME) and dispersive liquid–liquid microextraction (DLLME) methods based on applying low-density organic solvents have been critically compared for the speciation of inorganic selenium, Se(IV) (selenite) and Se(VI) (selenate) in environmental water samples by gas chromatography-flame ionization detection (GC-FID). At pH 2 and T = 75 °C for 7 min, only Se(IV) was able to form the piazselenol complex with 4-nitro-o-phenylenediamine. Piazselenol was extracted using an extraction solvent and was injected into a GC-FID instrument for the determination of Se(IV). Conveniently, Se(VI) remained in the aqueous phase. Total inorganic selenium was determined after the reduction of Se(VI) to Se(IV) and prior to the above procedures. The Se(VI) concentration was calculated as the difference between the measured total inorganic selenium and Se(IV) content. The effect of various experimental parameters on the efficiencies of the two methods and their optimum values were studied with the aid of response surface methodology and experimental design. Under the optimal conditions, the limit of detections (LODs) for Se(IV) obtained by USAEME-GC-FID and DLLME-GC-FID were 0.05 and 0.11 ng mL⁻¹, respectively. The relative standard deviations (RSDs, n = 6) for the measurement 10 ng mL⁻¹ of Se(IV) were 5.32% and 4.57% with the enrichment factors of 2491 and 1129 for USAEME-GC-FID and DLLME-GC-FID, respectively. Both methods were successfully applied to the analysis of inorganic selenium in different environmental water samples and certified reference material (NIST SRM 1643e).     

Speciation of inorganic selenium in environmental water samples by inductively coupled plasma optical emission spectrometry after preconcentration by using a mesoporous zirconia coating on coal cinder

A simple, novel, and selective flow‐injection solid‐phase extraction with inductively coupled plasma optical emission spectrometry method was developed for the speciation of inorganic selenium in environmental water samples. A mesoporous zirconia film was simply introduced to coat coal cinder by means of the sol–gel technique, and the adsorptive performance of the coated material for Se(IV)/Se(VI) was investigated in different media. Both Se(IV) and Se(VI) can be retained quantitatively by the material in HCl/NaOH (pH 1.0–9.0) media, while only Se(IV) was adsorbed quantitatively in sodium acetate buffer (pH 3.5–6.0). Thus, the assay of Se(VI) is based on subtracting Se(IV) from total selenium by controlling different adsorptive media without employing any redox procedure. Under the optimum conditions, the detection limit of Se(IV) is 9.0 ng/L with an enrichment factor of 100, and the relative standard deviation is 3.6% (n = 9, C = 5.0 ng/mL). The developed method was successfully applied to the speciation of inorganic selenium in environmental water samples with satisfactory results. In order to further verify the accuracy of the developed method, it was applied to analysis of total selenium in GSBZ 50031–94 certified reference environmental water, and the determined values coincided with the certified values very well.     

Exploring the elution mechanism of selenium species on liquid chromatography

In the present work, the chromatographic behavior of eight selenium species, namely selenites (Se(IV)), selenates (Se(VI)), seleno‐DL ‐methionine (Se‐Met), selenocystine (Se‐Cyst), selenocystamine (Se‐CM), selenourea (Se‐U), dimethylselenide ((CH₃)₂Se) and dimethyldiselenide ((CH₃)₂Se₂), was investigated under different stationary and mobile phase conditions, in an effort to unravel secondary interferences in their underlying elution mechanism. For this purpose, two end‐capped and a polar‐embedded reversed‐phase stationary phases were employed using different mobile phase conditions. Retention factors (log k_w) were compared with octanol–water distribution coefficients (log D) as well as with log k_w values on two immobilized artificial membrane (IAM) columns and two immobilized artificial plasma proteins stationary phases, obtained in our previous work. The role of electrostatic interactions was confirmed by introducing the net charge of the investigated Se species as an additional term in the log k_w/log D interrelation, which in most cases proved to be statistically significant. Principal component analysis of retention factors on all stationary phases and octanol–water log D values, however, showed that the elution of the investigated selenium species is mainly governed by partitioning mechanism under all different chromatographic conditions, while the pH of the mobile phase and the special column characteristics have only a minor effect.     

Voltammetric determination of Se(IV) and Se(VI) in saline samples—Studies with seawater, hydrothermal and hemodialysis fluids

Determination of Se(IV) and Se(VI) in high saline media was investigated by cathodic stripping voltammetry (CSV). The voltammetric method was applied to assay selenium in seawater, hydrothermal and hemodialysis fluids. The influence of ionic strength on selenium determination is discussed. The CSV method was based on the co-electrodeposition of Se(IV) with Cu(II) ions and Se(VI) determined by difference after sample UV-irradiation for photolytic selenium reduction. UV-irradiation was also used as sample pre-treatment for organic matter decomposition. Detection limit of 0.030 μg L⁻¹ (240 s deposition time) and relative standard deviation (RSD) of 6.19% (n = 5) for 5.0 μg L⁻¹ of Se(IV) were calculated. Linear calibration range for selenium was observed from 1.0 to 100.0 μg L⁻¹. Concerning the pre-treatment step, best results were obtained by using 60 min UV-irradiation interval in H₂O₂/HCl medium. Se(VI) was reduced to the Se(IV) electroactive species with recoveries between 91.7% and 112.9%. Interferents were also investigated.     

On-line separation and preconcentration of inorganic arsenic and selenium species in natural water samples with CTAB-modified alkyl silica microcolumn and determination by inductively coupled plasma-optical emission spectrometry

A new, simple, and selective method has been presented for the separation and preconcentration of inorganic arsenic (As(III)/As(V)) and selenium (Se(IV)/Se(VI)) species by a microcolumn on-line coupled with inductively coupled plasma-optical emission spectrometry (ICP-OES). Trace amounts of As(V) and Se(VI) species were separated and preconcentrated from total As and Se at desired pH values by a conical microcolumn packed with cetyltrimethylammonium bromide (CTAB)-modified alkyl silica sorbent in the absence of chelating reagent. The species adsorbed by CTAB-modified alkyl silica sorbent were quantitatively desorbed with 0.10 ml of 1.0 mol l⁻¹ HNO₃. Total inorganic arsenic and selenium were similarly extracted after oxidation of As(III) and Se(IV) to As(V) and Se(VI) with KMnO₄ (50.0 μmol l⁻¹). The assay of As(III) and Se(IV) were based on subtracting As(V) and Se(VI) from total As and total Se, respectively. All parameters affecting the separation/preconcentration of As(V) and Se(VI) including pH, sample flow rate and volume, eluent solution and volume have been studied. With a sample volume of 3.0 ml, the sample throughput was 24 h⁻¹ and the enrichment factors for As(V) and Se(VI) were 26.7 and 27.6, respectively. The limits of detection (LODs) were 0.15 μg l⁻¹ for As(V) and 0.10 μg l⁻¹ for Se(VI). The relative standard deviations (RSDs) for nine replicate determinations at 5.0 μg l⁻¹ level of As(V) and Se(VI) were 4.0% and 3.6%, respectively. The calibration graphs of the method for As(V) and Se(VI) were linear in the range of 0.5–1000.0 μg l⁻¹ with a correlation coefficient of 0.9936 and 0.9992, respectively. The developed method was successfully applied to the speciation analysis of inorganic arsenic and selenium in natural water samples with satisfactory results.