Electrochemical Determination of Boron in Natural Waters

Abstract

A sensitive voltammetric method for the determination of trace boron, based on the formation of the complex of boric acid with 4‐hydroxy‐5‐[salicylideneamino]‐2‐7‐naphthalenedisulfonic acid (azomethine H) is described. The reduction of the boric acid‐azomethine H complex at a hanging mercury drop electrode was exploited by square wave voltammetry (SWV) and cyclic voltammetry to determine boron in natural water samples, which were collected in the regions surrounding the boron mines of Central Anatolia. A reduction peak that belongs to the boric acid‐azomethine H complex at this electrode was observed at ?1.05 V vs. Ag/AgCl/KCl_(sat.). The effects of various parameters, such as ligand concentration, boric acid concentration, and formation time of the boric acid‐azomethine H complex, were investigated. Electrochemical experiments were conducted in 1.0 M HOAc/0.5 M NH₄OAc buffer at pH of 4.4±0.2. Linear working range was established by regression analysis between 5.0×10^?8 M and 1.0×10^?4 M. The probable metal cation interferences in water samples were eliminated by adding EDTA (ethylenediaminetetraacetic acid) to the samples. Data obtained using the square wave voltammetric (SWV) technique was compared statistically with inductively coupled plasma mass spectroscopy (ICP‐MS) data. Evaluation of the method based on statistical data was performed and the values of the limit of detection (LOD) and limit of quantitation (LOQ) were found to be 4.17×10^?6 M and 1.39×10^?5 M, respectively.     

Water Mediated Domino Knoevenagel‐Michael‐cyclocondensation Reaction of Malononitrile,Various Aldehydes and Barbituric Acid Derivatives Using Boric Acid Aqueous Solution System Compared with Nano‐titania Sulfuric Acid

Nano‐titania sulfuric acid (TSA) and boric acid [B(OH)₃] were efficiently utilized for domino Knoevenagel‐Michael‐cyclocondensation reaction of malononitrile, various aldehydes and barbituric acid derivatives to synthesis of pyrano[2,3‐d]pyrimidine diones. It is interesting that in boric acid aqueous solution system, H⁺ which abstracted from water by the interaction with B(OH)₃, efficiently catalyzed the reaction.     

Electrochemical Determination of Boric Acid Using the Boric Acid–Tiron Complexation System

For monitoring the boron concentration in reverse osmosis (RO) water produced by desalination plants, a voltammetric determination method for the amount of electrochemically inactive boron has been developed by using the complexation with 4,5‐dihydroxybenzene‐1,3‐disulfonic acid (Tiron). Cyclic voltammetric measurements showed the oxidation peak of boric acid–Tiron 1 : 1 complex at 920 mV. This peak was successfully applied to the determination of boron in RO water with the LOD of 0.1 mg B dm^?3 by using differential pulse voltammetry. The redox and acid–dissociation behaviors of Tiron and its boron complex are found to depend on the properties of pH buffer reagent.     

Determination of Uric Acid in Human Urine by Ion‐exclusion Chromatography with UV Detection Using Pure Water as Mobile Phase

A simple, rapid and accurate ion‐exclusion chromatographic method coupled with a UV detector for the determination of uric acid in human urine samples has been developed. The separation was carried out on an ion‐exclusion column using only pure water as mobile phase. The detection wavelength was 254 nm and urine sample was injected directly without any pretreatment. Furthermore, the retention behavior of uric acid on the ion‐exclusion column was researched when pure water and 1 mmol·L^?1 HCl were used as mobile phase, respectively. The stability of uric acid was also further investigated within 28 days. In this method, the linear range of the calibration curve for uric acid was 0.25–100 mg·L^?1, and the detection limit calculated at S/N=3 was 0.02 mg·L^?1. The proposed ion‐exclusion chromatographic method has been used for the determination of uric acid in human urine.     

Flow Injection Determination of Humic Acid with Chemiluminescence Detection

Abstract

A very sensitive and fast flow injection chemiluminescence method, based on the oxidation of humic acid (HA) by 1,3‐dibromine‐5,5‐dimethylhydantion in the presence of glycine in alkaline medium, was developed for the determination of trace humic acids in water. A wide calibration range from 0.001 to 1.0 µg mL^?1 was obtained at the optimized conditions and the detection limit was as low as 0.5 ng mL^?1 of humic acids. Most of the foreign substances tested showed relatively high tolerance levels and the proposed method was successfully applied to the determination of humic acid in river water and tap water.     

Activity of SiDbCl in the Electrooxidation of Ascorbic Acid,Dopamine, and Uric Acid

Selective electroanalytical responses for ascorbic acid, dopamine and uric acid at a carbon modified electrode based on 3‐n‐propyl‐1‐azonia‐4‐azabicyclo[2.2.2]octane silsesquioxane chloride (SiDbCl) is reported. The overlapped peaks observed at an unmodified electrode are resolved into three well defined voltammetric peaks allowing the simultaneous determination of the three species. Detection limits of 37, 0.3 and 0.1 μmo L⁻¹ of ascorbic acid, dopamine and uric acid, respectively, were calculated from calibration curves based on differential pulse voltammetric experiments performed in Britton ‐ Robinson buffer solution at pH 7.04.     

A Novel Voltammetric Method for the Determination of Maleic Acid Using Silver Amalgam Paste Electrode

An efficient voltammetric method was developed for the determination of maleic acid at a silver amalgam paste electrode (AgA‐PE) in Britton–Robinson buffer pH 2.0. The experimental parameters, such as pH of Britton–Robinson buffer, type of the supporting electrolyte and activation of the electrode surface were optimized. Under the optimal conditions, a linear response was observed over the 2×10^?6–1×10^?4 mol L^?1 maleic acid concentration range, determination limit being 5×10^?7 mol L^?1. A highly stable response, with a relative standard deviation (RSD) of 1.6% for 45 repetitive measurements of 1×10^?4 mol L^?1 maleic acid showed that there was no apparent surface passivation indicating the suitability of the method. The method was successfully applied for direct determination of maleic acid in drinking and river water.     

Selective Detection of Ascorbic Acid Using Octacyanomolybdate‐Doped‐Glutaraldehyde‐Cross‐Linked Poly‐L‐Lysine Film Modified Glassy Carbon Electrode

The present work describes oxidation of ascorbic acid (AA) at octacyanomolybdate‐doped‐glutaraldehyde‐cross‐linked poly‐L ‐lysine (PLL‐GA‐Mo(CN) film modified glassy carbon electrode in 0.1 M H₂SO₄. The modified electrode has been successfully prepared by means of electrostatically trapping Mo(CN) mediator in the cationic film of glutaraldehyde‐cross‐linked poly‐L ‐lysine. The dependence of peak current of modified electrode in pure supporting indicates that the charge transfer in the film was a mixed process at low scan rates (5 to 200 mV s^?1), and kinetically restrained at higher scan rates (200 to 1000 mV s^?1). Cyclic voltammetry and rotating disk electrode (RDE) techniques are used to investigate the electrocatalytic oxidation of ascorbic acid and compared with its oxidation at bare and undoped PLL‐GA film coated electrodes. The rate constant of catalytic reaction k obtained from RDE analysis was found to be 9.5×10⁵ cm³ mol^?1 s^?1. The analytical determination of ascorbic acid has been carried out using RDE technique over the physiological interest of ascorbic acid concentrations with a sensitivity of 75 μA mM^?1. Amperometric estimation of AA in stirred solution shows a sensitivity of 15 μA mM^?1 over the linear concentration range between 50 and 1200 μM. Interestingly, PLL‐GA‐Mo(CN) modified electrode facilitated the oxidation of ascorbic acid but not responded to other electroactive biomolecules such as dopamine, uric acid, NADH, glucose. This unique feature of PLL‐GA‐Mo(CN) modified electrode allowed for the development of a highly selective method for the determination of ascorbic acid in the presence of interferents.     

Electrochemical Behavior of Chloranil Chemically Modified Carbon Paste Electrode. Application to the Electrocatalytic Determination of Ascorbic Acid

A p‐chloranil modified carbon paste electrode was constructed and the electrochemical behavior of this electrode was studied in the aqueous solution with different pH. From the E_1/2–pH diagram for this compound the values of formal potential E^0' and pK_a of some different redox and acid‐base couples depending on the solution pH were estimated. The diffusion coefficient, D, value for p‐chloranil was estimated 1.5×10^?7 cm² s^?1. It has been shown by direct current cyclic voltammetry and double potential step chronoamperometry, that this p‐chloranil incorporated carbon paste electrode, can catalyze the oxidation of ascorbic acid in the aqueous buffered solution. Under the optimum condition (pH 7.00), the oxidation of ascorbic acid at the surface of such an electrode occurs at a potential about 325 mV less positive than that at an unmodified carbon past electrode. The catalytic oxidation peak currents was linearly dependent on the ascorbic acid concentration and a linear calibration curve was obtained in the range of 7×10^?5 M–4×10^?3 M of ascorbic acid with a correlation coefficient of 0.9998. The limit of detection (3σ) was determined as 3.5×10 ^?5 M. This method was used as simple, selective and precise voltammetric method for determination of ascorbic acid in pharmaceutical preparations.     

Selective Detection of Dopamine Using Glassy Carbon Electrode Modified by a Combined Electropolymerized Permselective Film of Polytyramine and Polypyrrole‐1‐propionic Acid

A sensitive and selective electrochemical method for the determination of dopamine using a combined electropolymerized permselective film of polytyramine and polypyrrole‐1‐propionic acid on a glassy carbon (GC) electrode was developed. The formation of a “layer‐by‐layer” film has allowed for selective detection of dopamine in the presence of 3,4‐dihydroxyphenylalanine (L‐DOPA), DOPAC, ascorbic acid, uric acid, epinephrine and norepinephrine. The modified electrodes exhibited a detection limit of 100 nM with linearity ranging from 5×10^?6 to 5×10^?5 M. No cleaning step was required during the course of repeated measurement.     

Study on the Electrochemical Behavior of Dopamine and Uric Acid at a 2‐Amino‐5‐mercapto‐[1,3,4] Triazole Self‐Assembled Monolayers Electrode

Selected from a series of structurally related heteroaromatic thiols, a newly synthesized reagent 2‐amino‐5‐mercapto‐[1,3,4] triazole (MATZ) was used to fabricate self‐assembled monolayers (SAMs) on gold electrode for the first time. The MATZ/Au SAMs was characterized by electrochemical methods and scanning electronic microscopy (SEM). In 0.04 mol/L Britton–Robinson buffer solution (pH 5), the electrochemical behavior of dopamine showed a quasireversible process at the MATZ/Au SAMs with an electrode kinetic constant 0.1049 cm/s. However, the electrochemical reaction of uric acid at the SAMs electrode showed an irreversible oxidation process, the charge‐transfer kinetics of uric acid was promoted by the SAMs. By Osteryoung square‐wave voltammetry (OSWV), the simultaneous determination of dopamine and uric acid can be accomplished with an oxidation peak separation of 0.24 V, the peak current of dopamine and uric acid were linearly to its concentration in the range of 2.5×10^?6–5.0×10^?4 mol/L for dopamine and 1×10^?6–1×10^?4 mol/L for uric acid with a detection limit of 8.0×10^?7 mol/L for dopamine and 7.0×10^?7 mol/L for uric acid. The MATZ/Au SAMs electrode was used to detect the content of uric acid in real urine and serum sample with satisfactory results.     

Highly Sensitive and Selective Measurement of Bismuth in Seawater and Drug with 1,2‐Phenylenedioxydiacetic Acid by Cathodic Adsorptive Stripping Voltammetry

A new method is presented for determination of bismuth based on cathodic adsorptive stripping of complex bismuth with 1,2‐phenylenedioxydiacetic acid (PDA) at a hanging mercury drop electrode (HMDE). The effect of various parameters such as pH, concentration of ligand, accumulation potential and accumulation time on the selectivity and sensitivity were studied. The optimum conditions for determination of bismuth include nitric acid concentration 0.01 M, 8.0×10^?4 M PDA and accumulation time 120 s, accumulation potential of ?200 mV. The limits of detection are 0.25 and 0.05 nM, and responses are linear 1–1000 and 0.1–400 nM at t_acc of 60 and 120 s, respectively. Many common anions and cations do not interfere in the determination of bismuth. The method was applied to the determination of bismuth in some real samples such as sea – and spring water and drug.     

Simultaneous Determination of 4‐Chlorophenol and Oxalic Acid Using an Expanded Graphite‐Epoxy Composite Electrode

An expanded graphite‐epoxy composite electrode (EG‐Epoxy) was employed for the simultaneous determination of 4‐chlorophenol (4‐CP) and oxalic acid (OA) by using cyclic voltammetry (CV), chronoamperometry (CA), and differential pulse voltammetry (DPV). The results indicated that OA could be determined in the presence of the same concentrations of 4‐CP within the concentration range of 0.1 mM to 0.5 mM with a relative standard deviation (RSD) smaller than 5%. Electrode fouling occurred during CA for 4‐CP concentrations larger than 0.5 mM. The DPV method was used for the simultaneous determination of 4‐CP and OA before and after electrochemical oxidation by chronopotentiometry under galvanostatic conditions (j=0.04 mA cm^?2, t=2 h) of a tap water sample spiked with 0.19 mM 4‐CP and 0.1 M Na₂SO₄.     

FIA Determination of Paracetamol in Pharmaceutical Drugs by Using Gold Electrodes Modified with a 3‐Mercaptopropionic Acid Monolayer

A flow injection analysis (FIA) method for the determination of paracetamol in pharmaceutical drugs using a gold electrode modified with a self‐assembled monolayer (SAM) of 3‐mercaptopropionic acid is described. At optimized experimental conditions the dynamic concentration range was 0.15 to 15.0 mg L^?1 with a detection limit of 0.2 μg mL^?1 (S/N=3). The repeatability of current responses for injections of 10 μmol L^?1 paracetamol was evaluated to be 3.2% (n=30) and the analytical frequency was 180 h^?1. The lifetime of the modified electrode was found to be 15 days. The results obtained by using the proposed amperometric method for paracetamol determination in four different drug samples compared well with those found by spectrophotometry.     

Simultaneous Determination of Ascorbic Acid and Uric Acid by Using a PVC/TTF‐TCNQ Composite Electrode as Detector in a FIA System

A PVC/TTF‐TCNQ composite electrode has been employed as detector in a flow injection system. The proposed method allows the simultaneous detection of ascorbic acid (AA) and uric acid (UA) in mixtures by using a FIA system in a simple manner, without pre‐treatment or modified electrode. This method is based on the amperometric determination of (a) ascorbic acid at 0.15 V and (b) both analytes at 0.35 V, being the response linear in the range 1×10^?2–4×10^?4 M for both analytes with detection limits (S/N=3) of 1.2×10^?4 M and 8.1×10^?5 M for AA and UA, respectively.     

Highly Sensitive Differential Pulse Voltammetric Determination of Cd,Zn and Pb Ions in Water Samples Using Stable Carbon‐Based Mercury Thin‐Film Electrode

A new carbon‐based mercury thin‐film electrode consisting of screen‐printed carbon on a low temperature co‐fired ceramic substrate was made. Ex‐situ mercury deposition in a potassium thiocyanate solution was used. This approach an electrode with high long‐term stability (>500 measurement cycles) and reproducibility (≤2 %) for sensitive determination of ultra trace heavy metals, using differential pulse anodic stripping voltammetry. The detection limits were 0.25, 0.08 and 5.5 ng mL^?1 for Cd(II), Pb(II), and Zn(II), respectively. The method was applied to the determination of the analytes in water, wastewater, lake water, and certified reference material samples with satisfactory results.     

Simultaneous Voltammetric Determination of Uric Acid and Ascorbic Acid Using a Carbon‐Paste Electrode Modified with Multi‐Walled Carbon Nanotubes/Nafion and Cobalt(II)nitrosalophen

A composition of multiwalled carbon nanotube (MWCNT), Nafion and cobalt(II)‐5‐nitrosalophen (CoNSal) is applied for the modification of carbon‐paste electrode (CPE). The pretreated MWCNT is well dispersed in the alcoholic solution of Nafion under the ultrasonic agitation, and the resulted suspension is used as modifier (with 10% w/w) in the matrix of the paste electrode. The prepared electrode further modified by addition of 3 wt% of CoNSal. The resulted modified electrode is used as a sensitive voltammetric sensor for simultaneous determination of uric acid (UA) and ascorbic acid (AA). The electrode showed efficient electrocatalytic activity in lowering the anodic overpotentials and enhancement of the anodic currents. This electrode is able to completely resolve the voltammetric response of UA and AA. The effects of potential sweep rate and pH of the buffer solution on the response of the electrode, toward UA and AA, and the peak resolution is thoroughly investigated by cyclic and differential pulse voltammetry (CV and DPV). The best peak resolution for these compounds using the modified electrode is obtained in solutions with pH 4. The ΔE_p for UA and AA in these methods is about 315 mV, which is considerably better than previous reports for these compounds. A linear dynamic range of 1×10^?7 to 1×10^?4 M with a detection limit of 6×10^?8 M is resulted for UA in buffered solutions with pH 4.0. The voltammetric response characteristics for AA are obtained as, the linear range of 5×10^?7 to 1×10^?4 M with the detection limit of 1×10^?7 M. The voltammetric detection system was very stable and the reproducibility of the electrode response, based on the six measurements during one month, was less than 3.5% for the slope of the calibration curves of UA and AA. The prepared modified electrode is successfully applied for the determination of AA and UA in mixture samples and reasonable accuracies are resulted.     

Fabrication and Application of a Novel Modified Electrode Based on Multiwalled Nanotubes/Cerium(III) 12‐Tungstophosphoric Acid Nanocomposite

A novel multiwalled nanotubes (MWNTs)/Cerium(III) 12 ‐ tungstophosphoric acid (CePW) nanocomposite film glassy carbon electrode was prepared in this paper. Electrochemical behaviors of the CePW/MWNTs modified electrode were investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). This modified electrode brought new capabilities for electrochemical devices by combining the advantages of carbon nanotubes, rare‐earth, and heteropoly‐acids. The results demonstrated that the CePW/MWNTs modified electrode exhibited enhanced electrocatalytic behavior and good stability for the detection of guanine and adenine in 0.1 M PBS (pH 7.0). The experimental parameters were optimized and a direct electrochemical method for the simultaneous determination of guanine and adenine was proposed. The detection limit (S/N=3) for guanine and adenine was 2.0×10^?8 M and 3.0×10^?8 M, respectively. Further, the acid‐denatured calf thymus DNA was also detected and the result was satisfied.     

Development of an Amperometric Biosensor for β‐N‐Oxalyl‐L‐α,β‐Diaminopropionic Acid (β‐ODAP)

An amperometric method for the determination of the neurotoxic amino acid β‐N‐oxalyl‐L ‐α,β‐diaminopropionic acid (β‐ODAP) using a screen printed carbon electrode (SPCE) is reported. The electrode material was bulk‐modified with manganese dioxide and used as a detector in flow injection analysis (FIA). The enzyme glutamate oxidase (GlOx) was immobilized in a Nafion‐film on the electrode surface. The performance of the biosensor was optimized using glutamate as an analyte. Optimum parameters were found as: operational potential 440 mV (vs. Ag/AgCl), flow rate 0.2 mL min^?1, and carrier composition 0.1 mol L^?1 phosphate buffer (pH 7.75). The same conditions were used for the determination of β‐ODAP. The signal was linear within the concentration range 53–855 μmol L^?1 glutamate and 195–1950 μmol L^?1 β‐ODAP. Detection limits (as 3σ value) for both analytes were 9.12 and 111.0 μmol L^?1, respectively, with corresponding relative standard deviations of 3.3 and 4.5%. The biosensor retained more than 73% of its activity after 40 days of on‐line use.     

Electrocatalytic Oxidation and Voltammetric Determination of L‐Cysteic Acid at the Surface of p‐Bromanil Modified Carbon Paste Electrode

The electrochemical properties of L ‐cysteic acid studied at the surface of p‐bromanil (tetrabromo‐p‐benzoquinone) modified carbon paste electrode (BMCPE) in aqueous media by cyclic voltammetry (CV) and double step potential chronoamperometry. It has been found that under optimum condition (pH 7.00) in cyclic voltammetry, the oxidation of L ‐cysteic acid at the surface of BMCPE occurs at a half‐wave potential of p‐bromanil redox system (e.g., 100 mV vs. Ag|AgCl|KCl_sat), whereas, L ‐cysteic acid was electroinactive in the testing potential ranges at the surface of bare carbon paste electrode. The apparent diffusion coefficient of spiked p‐bromanil in paraffin oil was also determined by using the Cottrell equation. The electrocatalytic oxidation peak current of L ‐cysteic acid exhibits a linear dependency to its concentration in the ranges of 8.00×10^?6 M–6.00×10^?3 M and 5.2×10^?7 M–1.0×10^?5 M using CV and differential pulse voltammetry (DPV) methods, respectively. The detection limits (2σ) were determined as 5.00×10^?6 M and 4.00×10^?7 M by CV and DPV methods. This method was used as a new, selective, rapid, simple, precise and suitable voltammetric method for determination of L ‐cysteic acid in serum of patient's blood with migraine disease.