Application of surfactant modified zeolite membrane electrode towards potentiometric determination of perchlorate

Potentiometric electrodes based on the incorporation of surfactant-modified zeolite Y (SMZ) particles into poly vinyl chloride (PVC) membranes were described. The electrode characteristics were evaluated regarding the response towards perchlorate ions. PVC membranes plasticized with dioctyl phthalate and without lipophilic additives (co-exchanger) are used throughout this study. The influence of membrane composition on the electrode response was studied. The electrode exhibited a Nernstian response towards perchlorate in the concentration range of 7.9 × 10⁻⁶–8.0 × 10⁻² M with a slope of 59.7 ± 0.9 mV per decade of perchlorate concentration with a working pH range of 1.7–9.5 with a fast response time of ≤10 s. The lower and upper detection limits were 4.07 × 10⁻⁷ and 0.13 M, respectively. The electrode response to perchlorate remains constant in the temperature range of 20–40 °C and in the presence of 2.5 × 10⁻⁶–1 × 10⁻² M NaNO₃. The selectivity coefficients for perchlorate anion as test species with respect to other anions were determined. The proposed modified zeolite-PVC electrode can be used for at least 30 days without any considerable divergence in potential. It was applied as indicator electrode in water samples with satisfactory results. The results of this study and our previous work show HDTMA plays different roles according to the zeolite type and matrix, as HDTMA-zeolite Y in a carbon paste matrix showed a good Nernstian behavior towards phosphate anion.     

Fabrication of functionalized carbon nanotube modified glassy carbon electrode and its application for selective oxidation and voltammetric determination of cysteamine

The functionalized carbon nanotube electrode was fabricated by electrodeposition of 1,2-naphthoquinone-4-sulfonic acid sodium (Nq) on single-wall carbon nanotube (SWNT) modified glassy carbon electrode (GCE). This electrode was characterized by scanning electron microscopy (SEM) and the results showed that Nq can rapidly and effectively be deposited on the surface of SWNT film with high stability. The electrochemical properties of functionalized SWNT/GCE with Nq (SWNT–Nq/GCE) were studied using cyclic voltammetry, double step potential chronoamperometry and differential pulse voltammetry methods. The results indicated that SWNT could improve the electrochemical behavior of Nq and greatly enhances its redox peak currents. The SWNT–Nq/GCE exhibited a pair of well-defined redox peaks. The experimental results also demonstrated that the Nq deposited species on SWNT could catalyze cysteamine oxidation and SWNT–Nq exhibited a high performance with lowering the overpotential by more than 710 mV. The effect of pH value, number of scans and Nq concentration were investigated on the electrochemical behavior of cysteamine. The selectivity of the reaction has been assessed with no interference from tyrosine, lysine, methionine, tryptophan, alanine and glutathione. The presented method has highly selectivity for voltammetric detection of cysteamine in the dynamic range from 5.0 × 10⁻⁶ M to 2.7 × 10⁻⁴ M and with a detection of limit (3σ) 3.0 × 10⁻⁶ M.     

Silver nanoparticles modified carbon nanotube paste electrode for simultaneous determination of dopamine and ascorbic acid

A novel modified carbon-paste electrode was employed for the simultaneous determination of dopamine (DA) and ascorbic acid (AA) with good selectivity and high sensitivity. Silver nanoparticle and carbon nanotube modified carbon-paste electrode (Ag/CNT–CPE) displayed excellent electrochemical catalytic activities towards dopamine (DA) and ascorbic acid (AA). The oxidation overpotentials of DA and AA were decreased significantly compared with those obtained at the bare CPE. Differential pulse voltammetry was used for the simultaneous determination of DA and AA. The peak separation between DA and AA was 67 mV. The calibration curves for DA and AA were obtained in the range of 8.0 × 10⁻⁷–6.4 × 10⁻⁵ M and 3.0 × 10⁻⁵–2.0 × 10⁻³ M, respectively. The lowest detection limits (S/N = 3) were 3.0 × 10⁻⁷ M and 1.2 × 10⁻⁵ M for DA and AA, respectively. Method was applied to the determination of DA and AA in real samples.     

A differential pulse voltammetric method for simultaneous determination of ascorbic acid,dopamine, and uric acid using poly (3-(5-chloro-2-hydroxyphenylazo)-4,5-dihydroxynaphthalene-2,7-disulfonic acid) film modified glassy carbon electrode

A stable modified glassy carbon electrode based on the poly 3-(5-chloro-2-hydroxyphenylazo)-4,5-dihydroxynaphthalene-2,7-disulfonic acid (CDDA) film was prepared by electrochemical polymerization technique to investigate its electrochemical behavior by cyclic voltammetry. The properties of the electrodeposited films, during preparation under different conditions, and their stability were examined. The homogeneous rate constant, k_s, for the electron transfer between CDDA and glassy carbon electrode was calculated as 5.25(±0.20) × 10² cm s⁻¹. The modified electrode showed electrocatalytic activity toward ascorbic acid (AA), dopamine (DA), and uric acid (UA) oxidation in a buffer solution (pH 4.0) with a diminution of their overpotential of about 0.12, 0.35, and 0.50 V for AA, DA, and UA, respectively. An increase could also be observed in their peak currents. The modified glassy carbon electrode was applied to the electrocatalytic oxidation of DA, AA, and UA, which resolved the overlapping of the anodic peaks of DA, AA, and UA into three well-defined voltammetric peaks in differential pulse voltammetry (DPV). This modified electrode was quite effective not only for detecting DA, AA, and UA, but also for simultaneous determination of these species in a mixture. The separation of the oxidation peak potentials for ascorbic acid–dopamine and dopamine–uric acid were about 0.16 V and 0.17 V, respectively. The final DPV peaks potential of AA, DA and UA were 0.28, 0.44, and 0.61 V, respectively. The calibration curves for DA, AA, and UA were linear for a wide range of concentrations of each species including 5.0–240 μmol L⁻¹ AA, 5.0–280 μmol L⁻¹ DA, and 0.1–18.0 μmol L⁻¹ UA. Detection limits of 1.43 μmol L⁻¹ AA, 0.29 μmol L⁻¹ DA and 0.016 μmol L⁻¹ UA were observed at pH 4. Interference studies showed that the modified electrode exhibits excellent selectivity toward AA, DA, and UA.     

Electroanalytical determination of sildenafil in Viagra tablets using screen-printed and conventional carbon paste electrodes

This work compares the electroactivity of a conventional carbon-paste electrodes and screen-printed carbon electrodes. Potentiometric sensors responsive to sildenafil citrate (SILC) drug (the active component of Viagra) are described, characterized, compared and used for drug assessment. The proposed carbon paste electrode is fully characterized in terms of plasticizer type, response time, life span, soaking time, titrant, pH and temperature. The electrodes exhibited linear response with a Nernstian slope of 58.20 ± 1 and 58.82 ± 0.5 mV decade⁻¹ for SILC in the concentration range from 1.0 × 10⁻⁷ to 1.0 × 10⁻² and 5.30 × 10⁻⁷ to 1.0 × 10⁻² mol L⁻¹ with good reproducibility for CPE and SPE, respectively. Both CPE and SPE could be used in the pH range 3.0–5.0 and the isothermal coefficient is found to be 0.98 and 0.85 mV/°C, respectively. The limit of detection was found to be 9.0 × 10⁻⁸ and 3.5 × 10⁻⁷ mol L⁻¹ for CPE and SPE, respectively. They were applied to potentiometric determination of SILC in pure state and pharmaceutical preparation under batch conditions. The CPE and SPE sensors display good selectivity for SILC drug over large number of inorganic cations, sugars and amino acids commonly used in drug formulations. The CPE and SPE show high selectivity for the drug under investigation. The results obtained using the fabricated CPE is compared with those obtained by SPE for spiked pharmaceutical samples.     

Preparation of poly N,N-dimethylaniline/ferrocyanide film modified carbon paste electrode: Application to electrocatalytic oxidation of l-cysteine

Functionalized poly N,N-dimethylaniline film was prepared by adsorption of ferrocyanide onto the polymer forming at the surface of carbon paste electrode (CPE) in aqueous solution. The electrocatalytic ability of poly N,N-dimethylaniline/ferrocyanide film modified carbon paste electrode (PDMA/FMCPE) was demonstrated by oxidation of l-cysteine. Cyclic voltammetry and chronoamperometry techniques were used to investigate this ability. In the optimum pH (6.00), the electrocatalytic ability about 480 mV and the catalytic reaction rate constant, (k_h), can be seen 3.08 × 10³ M⁻¹ s⁻¹. The catalytic oxidation peak current determined by cyclic voltammetry method was linearly dependent on the l-cysteine concentration and the linearity range obtained was 8.00 × 10⁻⁵ –2.25 × 10⁻³ M. Detection limit of this method was determined as 6.17 × 10⁻⁵ M (2σ). At a fixed potential under hydrodynamic conditions (stirred solution), the calibration plot was linear over the l-cysteine concentration range 7.40 × 10⁻⁶ M–1.38 × 10⁻⁴ M. The detection limit of the method was 6.38 × 10⁻⁶ M (2σ).     

Selective electrochemical sensing of calcium dobesilate based on an ordered mesoporous carbon-modified pyrolytic graphite electrode

Cyclic voltammetric investigation of calcium dobesilate (CD) in aqueous acid media was carried out by using an ordered mesoporous carbon-modified pyrolytic graphite electrode (OMC/PGE). A pair of well-defined redox peaks of CD was observed at the OMC/PGE, showing its good elelctrochemial response towards CD. The anodic current is linear with CD concentration in the range of 1.0 × 10⁻⁷–1.3 × 10⁻³ mol L⁻¹, with a detection limit of 4.0 × 10⁻⁸ mol L⁻¹. Meanwhile, the proposed electrode can avoid some interference coexisting with CD, such as uric acid, serotonin, and ascorbic acid. The proposed method can be potentially applied for selective electrochemical sensing of CD in physiological condition.     

MWNT/Nafion composite modified glassy carbon electrode as the voltammetric sensor for sensitive determination of 8-hydroxyquinoline in cosmetic

In this paper, a multiwall carbon nanotube/Nafion composite modified glassy carbon electrode (MWNT/Nafion/GCE) was used as a voltammetric sensor to determine 8-hydroxyquinoline (8-HQ) in cosmetic. This voltammetric sensor exhibited strong catalytic effect toward the oxidation of 8-HQ and caused an anodic peak at 0.97 V in HAc-NaAc buffer solution (0.2 M, pH 3.6). Under the optimized condition, the anodic peak current was linear with the concentration of 8-HQ in the range of 2 × 10⁻⁸ M–1.0 × 10⁻⁵ M. The detection limit was 9 × 10⁻⁹ M. The practical application of MWNT/Nafion/GCE was carried out for determining 8-HQ in cosmetic sample with satisfactory results. The electrode reaction mechanism was studied by cyclic voltammetry and UV–vis spectra.     

Determination of trace vanadium(V) by adsorptive anodic stripping voltammetry on an acetylene black paste electrode in the presence of alizarin violet

A sensitive and simplified voltammetric method is developed for the determination of trace amounts of vanadium(V) by adsorptive anodic stripping voltammetry using an acetylene black (AB) paste electrode. The method is based on the preconcentration of the V(V)–alizarin violet (AV) complex at open circuit while stirring the solution for 90 s in 0.15 mol dm⁻³ hexamethylenetetraamine–hydrochloric acid buffer (pH 4.4), the adsorbed complex is then oxidized, producing a response with a peak potential of 564 mV when scanning linearly from 0 to 1000 mV. For voltammetric determination of V(V), the parameters influencing the peak current have been optimized. Under the selected conditions, the peak current and concentration of V(V) accorded with linear relationship in the range of 8.0 × 10⁻¹⁰ mol dm⁻³–1.0 × 10⁻⁷ mol dm⁻³ (c_AV = 2.0 × 10⁻⁶ mol dm⁻³) and 1.0 × 10⁻⁷ mol dm⁻³–8.0 × 10⁻⁶ mol dm⁻³ (c_AV = 2.0 × 10⁻⁵ mol dm⁻³), the detection limit (three times signal to noise) was estimated to be 6.0 × 10⁻¹⁰ mol dm⁻³ for 90 s accumulation. The relative standard deviation (RSD) is 1.9% and 2.3% for V(V) concentrations of 1.0 × 10⁻⁷ mol dm⁻³ and 1.0 × 10⁻⁸ mol dm⁻³ respectively. Finally, this proposed method was successfully applied to the determination of V(V) in natural water samples.     

Selective determination of dopamine in the presence of ascorbic acid at a multi-wall carbon nanotube-poly(3,5-dihydroxy benzoic acid) film modified electrode

A sensitive and selective method for determination of dopamine (DA) using multi-wall carbon nanotube (MWCNT)-poly(3,5-dihydroxy benzoic acid) [poly(DBA)] modified electrode is developed. The modified electrode shows excellent electrocatalytic activity toward the oxidation of dopamine in phosphate buffer solutions at pH 7.4. Using cyclic voltammetry, the linear range of 1 × 10⁻⁷–7.0 × 10⁻⁵ M in the interference of 500 μM ascorbic acid (AA) and the detection limit of 1.0 × 10⁻⁸ M were estimated for the measurement of DA in pH 7.4 phosphate buffer solutions. The value of DA current retained 98.36% of the initial response current after the modified electrode exposed to the air for one week. The interference studies showed that the modified electrode excludes effectively large excess of AA. The kinetic characteristics of the transfer of DA demonstrated that the electron propagation between DA and electrode was accelerated at MWCNT-poly(DBA) modified electrode. The work provided a valid and simple approach to selectively detect dopamine in the presence of AA in physiological environment.     

The role of bromine adlayer at palladium electrode in the electrochemical oxidation of dopamine in alkaline solution

A palladium electrode modified with bromine monolayer was fabricated throughout a spontaneous oxidative chemisorption of bromide ions contained in an alkaline solution. The surface coverage and the apparent double layer capacitance induced by the adsorption of bromide ions under the present applied potential indicates the formation of incomplete monolayer due to a prominent co-adsorption of hydroxyl ions (OH⁻). The film modified electrode exhibited a substantial reactivity and high sensitivity in the electrochemical oxidation of dopamine (DA) in the presence of ascorbic acid (AA) and uric acid (UA). This trend was attributed to the structure and the composition of the bromine adlayer which renders a partial negative charge capable of attracting selectively the cationic DA and repelling anionic AA and UA. The peak currents of DA in the binary and ternary mixtures were well-separated, well-defined and increased linearly with respect to its concentration. The interference property expected by the presence of both AA and UA has been advantageously eliminated at the bromine-adlayer modified electrode. The apparent diffusion coefficient value of DA was 1.37 × 10⁻⁸ m² s⁻¹, based on an amperometric current–time study. The present system provides a simple and fundamental approach for the simultaneous and selective determination of DA in the presence of AA and UA.     

Electrochemical layer-by-layer modified imprinted sensor based on multi-walled carbon nanotubes and sol–gel materials for sensitive determination of thymidine

A novel electrochemical sol–gel imprinted sensor for sensitive and convenient determination of thymidine was developed. Thin film of molecularly imprinted sol–gel polymers with specific binding sites for thymidine was cast on carbon electrode by electrochemical deposition. Multi-walled carbon nanotubes (MWCNTs) were introduced for the enhancement of electronic transmission and sensitivity. The morphology and performance of the imprinted film was characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV) and amperometric measurements (i–t) in detail. The results showed that the imprinted film exhibited high selectivity toward thymidine. The linear range is over the range from 2 to 22 μmol L⁻¹, and the linear regression equation for thymidine is I = 0.867C + 0.232 with the detection limit of 1.6 × 10⁻⁹ mol L⁻¹(S/N = 3). The imprinted sensor was successfully employed to detect thymidine in some zidovudine-tablet samples.     

Flow electroanalytical system based on cyclam-modified graphite felt electrodes for lead detection

A flow sensor for trace analysis of lead, using cyclam-modified graphite felt as working electrode is reported here. The detection is performed in two steps: the preconcentration of Pb²⁺ ions by complexation with immobilized cyclam and the analysis by linear sweep stripping voltammetry. Cyclam ligands are covalently immobilized onto the graphite felt by chemical reactions on amino acid linkers, previously attached to the electrode by an electrochemical process. A surface concentration of about 12% is estimated by cyclic voltammetry analyses, using redox probes. The factors, affecting the performances of the flow sensor are reported, such as the flow rate and the volume of the analyzed solution used during the preconcentration step. A calibration curve typical of an equilibrium process is obtained for lead ions with a limit of detection able to reach 2.5 × 10⁻⁸ mol L⁻¹, showing the ability of the cyclam-modified electrode to complex Pb²⁺ ions. The flow sensor shows a good selectivity toward lead in the presence of Cu²⁺ and Zn²⁺ ions.     

Electrochemistry of magnolol and interaction with DNA

The electrochemical behaviors of magnolol have been studied at glassy carbon electrode using cyclic voltammetry, linear sweep voltammetry and chronocoulometry. Moreover, its interaction with DNA was investigated in solution by electrochemical methods and ultraviolet–visible spectroscopy. The experiment results indicated that the electrochemical oxidation of magnolol was an irreversible process with one proton and one electron transfer. The electron transfer coefficient (α) was calculated to be 0.441 ± 0.001. At the scan rate from 100 mV/s to 450 mV/s, the electrode process was controlled by the adsorption step and at the range of 600–950 mV/s the electrochemical oxidation was diffusion controlled process. The corresponding electrochemical rate constant (k_s) was 0.0760 ± 0.0001 s⁻¹. Through chronocoulometry experiment, the diffusion coefficient (D) and the surface concentration (Γ) were obtained as (3.76 ± 0.01) × 10⁻⁷ cm²/s and (2.98 ± 0.01) × 10⁻¹⁰ mol/cm². In addition, the interaction of magnolol and DNA was ascribed to be electrostatic interaction and the calculated association constant (β) and Hill coefficient (m) were 1.14 × 10⁵ M⁻¹ and 0.973. At last a sensitive and convenient electrochemical method was proposed for the determination of magnolol.     

Electron transfer kinetics and morphology of cytochrome c at the biomimetic phospholipid layers

Electrochemistry of cytochrome c (cyt c) at biomimetic phospholipid layers was studied in a phosphate buffer solution, which were formed with dilauroyl phosphatidic acid (DLPA, C12:0), dipalmitoyl phosphatidic acid (DPPA, C16:0), distearoyl phosphatidic acid (DSPA, C18:0), and palmitoyl–oleoyl phosphatidic acid (POPA, C16:0–18:1). The lipid-layers formed firstly at the air/water interface were immediately transferred onto the electrode surface using the Langmuir–Blodgett (LB) technique. The electrochemical properties of cyt c at the lipid covered electrodes depended on the orientation, number of layers of phospholipids, tail (or head) group down, and vice versa. Atomic force microscopy (AFM) images of cyt c adsorbed on the POPA monolayer (showing the head group diameter of POPA to be ca. 0.7 nm) formed on highly oriented pyrolytic graphite (HOPG) displayed uniform surface morphology of lipid layer and clumps of aggregated cyt c molecules with a minimum size corresponding to four cyt c molecules. The heterogeneous electron transfer rate constants, k⁰ values, of cyt c were determined to be 1.02 × 10⁻³, 0.98 × 10⁻³, and 0.67 × 10⁻³ cm/s for the lipid monolayer in the tail down orientation (X-type) of POPA, DLPA, and DPPA, and 0.67 × 10⁻³ and 0.50 × 10⁻³ cm/s for the head down orientation (Z-type) of POPA and DLPA monolayers, respectively.     

Electrochemical impedimetry of electrodeposited poly(propylene imine) dendrimer monolayer

Voltammetric and electrochemical impedance spectroscopic (EIS) studies of generation one poly(propylene imine) (G1 PPI) dendrimer as an electroactive and catalytic nanomaterials both in solution and as an electrode modifier based on a simple one step electrodeposition method is presented. The G1 PPI exhibited a reversible one electron redox behaviour at E^0′ ca 210 mV in phosphate buffer pH 7.2 with diffusion coefficient and Warburg coefficient of 7.5 × 10⁻¹⁰ cm² s⁻¹ and 8.87 × 10⁻⁴ Ω s^−1/2 respectively. Cyclic voltammetric electrodeposition of a monolayer of G1 PPI on glassy carbon electrode was carried out between −100 mV and 1100 mV for 10 cycles. The nanoelectrode was electroactive in PBS at E^0′ ca 220 mV. Kinetic profiles such as time constant (4.64 × 10⁻⁵ s rad⁻¹), exchange current (1.55 × 10⁻⁴ A) and heterogeneous rate constant (4.52 × 10⁻³ cm s⁻¹) obtained from EIS showed that the dendrimer layer catalysed the redox reaction of Fe^2+/3+ in [Fe(CN)₆]^3−/4− redox probe.     

Simultaneous determination of adenine and guanine utilizing PbO2-carbon nanotubes-ionic liquid composite film modified glassy carbon electrode

A novel and reliable electrochemical sensor based on PbO₂-carbon nanotubes-room temperature ionic liquid (i.e., 1-butyl-3-methylimidazolium hexafluorophosphate, BMIMPF6) composite film modified glassy carbon electrode (GCE) (PbO₂–MWNT–RTIL/GCE) was proposed for simultaneous and individual determination of guanine and adenine. The guanine and adenine oxidation responses were monitored by differential pulse voltammetric (DPV) measurement. Compared with the bare electrode, the PbO₂–MWNT–RTIL/GCE not only significantly enhanced the oxidation peak currents of guanine and adenine, but also lowered their oxidation overpotentials, suggesting that the synergistic effect of PbO₂, MWNT and RTIL could dramatically improve the determining sensitivity of guanine and adenine. The PbO₂–MWNT–RTIL/GCE showed good stability, high accumulation efficiency and enhanced electrocatalytic ability for the detection of guanine and adenine. Besides, the modified electrode also exhibited good behaviors in the simultaneous detection of adenine and guanine with the peak separation of 0.29 V in 0.1 M pH 7.0 phosphate buffer solution (PBS). Under the optimal conditions, the detection limit for individual determination of guanine and adenine was 6.0 × 10⁻⁹ M and 3.0 × 10⁻⁸ M (S/N = 3), respectively. The proposed method for the measurements of guanine and adenine in herring sperm DNA was successfully applied with satisfactory results.     

Development of a carbon nanotubes paste electrode modified with crosslinked chitosan for cadmium(II) and mercury(II) determination

A functionalized carbon nanotubes paste electrode modified with cross-linked chitosan for the determination of trace amounts of cadmium(II) and mercury(II) by linear anodic stripping voltammetry is described. Under optimal experimental conditions, the peak current was linear in the Cd(II) concentration range from 5.9 × 10⁻⁸ to 1.5 × 10⁻⁶ mol L⁻¹ with a detection limit of 9.8 × 10⁻⁹ mol L⁻¹ and, for Hg(II) from 6.7 × 10⁻⁹ to 8.3 × 10⁻⁸ mol L⁻¹with a detection limit of 2.4 × 10⁻⁹ mol L⁻¹. The proposed method was successfully applied for the determination of Hg(II) in natural and industrial wastewater samples, and Cd(II) in sediments, human urine, natural, and industrial wastewater samples.     

Speciation of Fe in Fe-modified zeolite catalysts

Fe-modified zeolites (ferrierite and MFI) were prepared by four impregnation methods followed by calcination and tested as catalysts in oxidative dehydrogenation of ethane by nitrous oxide at 350 °C. The Fe cationic and Fe oxidic species were identified by combination of UV–Vis spectroscopy and voltammetry. Monomeric or dimeric Fe ions have only UV absorption bands and some of them evolve voltammetrically identifiable [Fe(OH)_x]^(3−x)+ ions in contact with acetic acid-sodium acetate buffer. Fe oxide nanoclusters characterised by UV band at about 28,000 cm⁻¹ are not detected by voltammetry under chosen conditions because they are situated inside the zeolite channels. Amorphous, nanocrystalline, and crystalline Fe(III) oxides were distinguished sensitively by their specific voltammetric reduction peaks at potentials −0.1 to −0.8 V/SCE in acetate buffer (pH 4.7) and by phase-specific electron pair transitions responsible for Vis absorption band centred at 17,500–21,000 cm⁻¹. The proposed method to differentiation between these ferric oxides is novel in materials analysis and solid state speciation. The monomeric and dimeric ferric ions are active in oxidative dehydrogenation of ethane to ethene with selectivity about 40–60% under used conditions, while Fe oxide nanoclusters are too active and over-oxidise ethane and/or ethene to C, CO and CO₂. Oppositely to general expectations, ferric oxides are indifferent in the catalytic reaction and do not decrease reaction selectivity.     

Investigation of polarographic interference between Se(IV) and Cr(VI), its elimination and application to Gerede river water

Trace chromium(VI) determination plays an important role since it is carcinogenic agent and toxic pollutant. For this purpose a direct method is developed using differential pulse polarography, DPP. When selenite was added into solutions of some ions such as copper(II), lead(II), cadmium(II), zinc(II), and chromium(VI) their DP polarographic peak decreased. This kind of interference will cause large errors in the determinations, its elimination is very important. The interference between selenite and Cr(VI) ions could be eliminated in B-R (Britton-Robbinson) buffer at pH 8.5. In this work the effect of components present in buffer has been investigated and it was found that phosphate and borate eliminated the formation of Cr–Se intermetallic compound formation. While it was possible to determine 1 × 10⁻⁵ M Cr(VI) in the presence of 100 times more selenite as (1.0 ± 0.1) × 10⁻⁵ M, in borate medium, it was possible to determine (1.0 ± 0.05) × 10⁻⁵ M in phosphate medium. In the presence of selenite detection limit (S/N = 3) was 9.0 × 10⁻⁸ M Cr(VI) by using either phosphate or borate This method was applied to Gerede river water, after oxidation all Cr(III) present into Cr(VI).