Simultaneous voltammetric determination of paracetamol and caffeine in pharmaceutical formulations using a boron-doped diamond electrode

A simple and highly selective electrochemical method was developed for the single or simultaneous determination of paracetamol (N-acetyl-p-aminophenol, acetaminophen) and caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) in aqueous media (acetate buffer, pH 4.5) on a boron-doped diamond (BDD) electrode using square wave voltammetry (SWV) or differential pulse voltammetry (DPV). Using DPV with the cathodically pre-treated BDD electrode, a separation of about 550 mV between the peak oxidation potentials of paracetamol and caffeine present in binary mixtures was obtained. The calibration curves for the simultaneous determination of paracetamol and caffeine showed an excellent linear response, ranging from 5.0 × 10⁻⁷ mol L⁻¹ to 8.3 × 10⁻⁵ mol L⁻¹ for both compounds. The detection limits for the simultaneous determination of paracetamol and caffeine were 4.9 × 10⁻⁷ mol L⁻¹ and 3.5 × 10⁻⁸ mol L⁻¹, respectively. The proposed method was successfully applied in the simultaneous determination of paracetamol and caffeine in several pharmaceutical formulations (tablets), with results similar to those obtained using a high-performance liquid chromatography method (at 95% confidence level).     

Simultaneous determination of N-acetyl-p-aminophenol and p-aminophenol with poly(3,4-ethylenedioxythiophene) modified glassy carbon electrode

A sensitive and selective method was developed for the determination of N-acetyl-p-aminophenol (APAP) and p-aminophenol (PAP) using poly(3,4-ethylenedioxythiophene) (PEDOT)-modified glassy carbon electrode (GCE). Cyclic voltammetry and differential pulse voltammetry were used to investigate the electrochemical reaction of APAP and PAP at the modified electrode. Both APAP and PAP showed quasireversible redox reactions with formal potentials of 367 mV and 101 mV (vs. Ag/AgCl), respectively, in phosphate buffer solution of pH 7.0. The significant peak potential difference (266 mV) between APAP and PAP enabled the simultaneous determination both species based on differential pulse voltammetry. The voltammetric responses gave linear ranges of 1.0 × 10⁻⁶-1.0 × 10⁻⁴ mol L⁻¹ and 4.0 × 10⁻⁶-3.2 × 10⁻⁴ mol L⁻¹, with detection limits of 4.0 × 10⁻⁷ mol L⁻¹ and 1.2 × 10⁻⁶ mol L⁻¹ for APAP and PAP, respectively. The method was successfully applied for the determination of APAP and PAP in pharmaceutical formulations and biological samples.     

An electrochemiluminescent biosensor for glucose based on the electrochemiluminescence of luminol on the nafion/glucose oxidase/poly(nickel(II)tetrasulfophthalocyanine)/multi-walled carbon nanotubes modified electrode

A poly(nickel(II) tetrasulfophthalocyanine)/multi-walled carbon nanotubes composite modified electrode (polyNiTSPc/MWNTs) was fabricated by electropolymerization of NiTSPc on MWNTs-modified glassy carbon electrode (GCE). The modified electrode was found to be able to greatly improve the emission of luminol electrochemiluminescence (ECL) in a solution containing hydrogen peroxide. Glucose oxidase (GOD) was immobilized on the surface of polyNiTSPc/MWNTs modified GC electrode by Nafion to establish an ECL glucose sensor. Under the optimum conditions, the linear response range of glucose was 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 8.0 × 10⁻⁸ mol L⁻¹ (defined as the concentration that could be detected at the signal-to-noise ratio of 3). The ECL sensor showed an outstanding well reproducibility and long-term stability. The established method has been applied to determine the glucose concentrations in real serum samples with satisfactory results.     

The renewable bismuth bulk annular band working electrode: Fabrication and application in the adsorptive stripping voltammetric determination of nickel(II) and cobalt(II)

The paper presents the first report on fabrication and application of a user friendly and mercury free electrochemical sensor, with the renewable bismuth bulk annular band working electrode (RBiABE), in stripping voltammetry (SV). The sensor body is partly filled with the internal electrolyte solution, in which the RBiABE is cleaned and activated before each measurement. Time of the RBiABE contact with the sample solution is precisely controlled. The usefulness of this sensor was tested by Ni(II) and Co(II) traces determination by means of differential pulse adsorptive stripping voltammetry (DP AdSV), after complexation with dimethylglyoxime (DMG) in ammonia buffer (pH 8.2). The experimental variables (composition of the supporting electrolyte, pre-concentration potential and time, potential of the RBiABE activation, and DP parameters), as well as possible interferences, were investigated. The linear calibration graphs for Ni(II) and Co(II), determined individually and together, in the range from 1 × 10⁻⁸ to 70 × 10⁻⁸ mol L⁻¹ and from 1 × 10⁻⁹ to 70 × 10⁻⁹ mol L⁻¹ respectively, were obtained. The calculated limit of detection (LOD), for 30 s of the accumulation time, was 3 × 10⁻⁹ mol L⁻¹ for Ni(II) in case of a single element’s analysis, whereas the LOD was 5 × 10⁻⁹ mol L⁻¹ for Ni(II) and 3 × 10⁻¹⁰ mol L⁻¹ for Co(II), when both metal ions were measured together. The repeatability of the Ni(II) and Co(II) adsorptive stripping voltammetric signals obtained at the RBiABE were equal to 5.4% and 2.5%, respectively (n = 5). Finally, the proposed method was validated by determining Ni(II) and Co(II) in the certified reference waters (SPS-SW1 and SPS-SW2) with satisfactory results.     

A new method for electrocatalytic oxidation of ascorbic acid at the Cu(II) zeolite-modified electrode

A new method is developed for the catalytic oxidation of ascorbic acid at graphite zeolite-modified electrode, doped with copper(II) (Cu²⁺A/ZCME). Copper(II) exchanged in zeolite type A acts as catalyst to oxidize ascorbic acid. The modified electrode lowered the overpotential of the reaction by ∼400 mV. First, the electrochemical behavior of copper(II), incorporated in the zeolite type A modified electrode, was studied. The results illustrate that diffusion can control the copper(II)/copper(0) redox process at the Cu²⁺A/ZCME. Then, the behavior of electrocatalytic oxidation reaction for ascorbic acid was researched. The electrode was employed to study electrocatalytic oxidation of ascorbic acid, using cyclic voltammetry and chronoamperometry as diagnostic techniques. The diffusion coefficient of ascorbic acid was equal to 1.028 × 10⁻⁵ cm² s⁻¹. A linear calibration graph was obtained over the ascorbic acid with a concentration range of 0.003-6.00 mmol L⁻¹. The detection limit (DL) of ascorbic acid was estimated as 2.76 × 10⁻⁷ mol L⁻¹. The relative standard deviations of 10 replicate measurements (performed on a single electrode at several ascorbic acid concentrations between 3.0 and 200 μmol L⁻¹) were measured between 1.0 and 2.4%.     

Determination of chlorogenic acid in coffee using a biomimetic sensor based on a new tetranuclear copper(II) complex

A new tetranuclear copper(II) complex which mimics the active site of catechol oxidase was synthesized and characterized by IR, CHN, electronic spectroscopic and ¹H NMR methods. The title complex [Cu₂(μ-OH)(bpbpmp-NO₂)]₂[ClO₄]₂ was employed in the construction of a novel biomimetic sensor and used in the determination of chlorogenic acid by square wave voltammetry. The performance and optimization of the resulting biomimetic sensor were studied in detail. The best response of this sensor was obtained for 75:15:10% (w/w/w) ratio of the graphite powder:nujol:Cu(II) complex, 0.1 mol L⁻¹ phosphate buffer solution (pH 7.0), with frequency, pulse amplitude, and scan increment at 30 Hz, 100 mV, and 3.0 mV, respectively. The chlorogenic acid concentration was linear in the range of 5.0 × 10⁻⁶ to 1.45 × 10⁻⁴ mol L⁻¹ (r = 0.9985) with a detection limit of 8.0 × 10⁻⁷ mol L⁻¹. This biomimetic sensor demonstrated long-term stability (250 days; 640 determinations) and reproducibility, with a relative standard deviation of 10.0%. The recovery study of chlorogenic acid in coffee samples gave values from 93.2% to 106.1% and the concentrations determined showed good agreement when compared with those obtained using capillary electrophoresis at the 95% confidence level.     

Preliminary evaluation of monolithic column high-performance liquid chromatography with tris(2,2′-bipyridyl)ruthenium(II) chemiluminescence detection for the determination of quetiapine in human body fluids

High-performance liquid chromatography (HPLC) with tris(2,2′-bipyridyl)ruthenium(II) chemiluminescence detection methodology is reported for the determination of the atypical antipsychotic drug quetiapine and the observation of its major active and inactive metabolites in human urine and serum. The method uses a monolithic chromatographic column allowing high flow rates of 3 mL min⁻¹ enabling rapid quantification. Flow injection analysis (FIA) with tris(2,2′-bipyridyl)ruthenium(II) chemiluminescence detection and HPLC time of flight mass spectrometry (TOF-MS) were used for the determination of quetiapine in a pharmaceutical preparation to establish its suitability as a calibration standard. The limit of detection achieved with FIA was 2 × 10⁻¹¹ mol L⁻¹ in simple aqueous solution. The limits of detection achieved with HPLC were 7 × 10⁻⁸ and 2 × 10⁻¹⁰ mol L⁻¹ in urine and serum, respectively. The calibration range for FIA was between 5 × 10⁻⁹ and 1 × 10⁻⁶ mol L⁻¹. The calibration ranges for HPLC were between 1 × 10⁻⁷-1 × 10⁻⁴ and 1 × 10⁻⁸-1 × 10⁻⁴ mol L⁻¹ in urine and serum, respectively. The quetiapine concentrations in patient samples were found to be 3 × 10⁻⁶ mol L⁻¹ in urine and 7 × 10⁻⁷ mol L⁻¹ in serum. Without the need for preconcentration, the HPLC detection limits compared favourably with those in previously published methodologies. The metabolites were identified using HPLC-TOF-MS.     

Simultaneous determination of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) in food samples using a carbon composite electrode modified with Cu3(PO4)2 immobilized in polyester resin

A simple electrochemical method was developed for the single and simultaneous determination of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) in food samples using square-wave voltammetry (SWV). A carbon composite electrode modified (MCCE) with copper (II) phosphate immobilized in a polyester resin was proposed. The modified electrode allowed the detection of BHA and BHT at potentials lower than those observed at unmodified electrodes. A separation of about 430 mV between the peak oxidation potentials of BHA and BHT in binary mixtures was obtained. The calibration curves for the simultaneous determination of BHA and BHT demonstrated an excellent linear response in the range from 3.4 × 10⁻⁷ to 4.1 × 10⁻⁵ mol L⁻¹ for both compounds. The detection limits for the simultaneous determination of BHA and BHT were 7.2 × 10⁻⁸ and 9.3 × 10⁻⁸ mol L⁻¹, respectively. In addition, the stability and repeatability of the electrode were determined. The proposed method was successfully applied in the simultaneous determination of BHA and BHT in several food samples, and the results obtained were found to be similar to those obtained using the high performance liquid chromatography method with agreement at 95% confidence level.     

A novel Mn PVC membrane electrode based on a recently synthesized Schiff base

A new PVC membrane electrode for manganese(II) ion based on a recently synthesized Schiff base of 5-[(4-nitrophenylazo)-N-hexylamine]salicylaldimine is reported. The electrode exhibits a Nernstian response for Mn²⁺ ions over a wide concentration range (4.0 × 10⁻⁷ to 1.8 × 10⁻² mol L⁻¹) with a slope of 30.1 (±1.0). The limit of detection is 1.0 × 10⁻⁷ mol L⁻¹. The electrode has a fast response time (∼10 s), a satisfactory reproducibility and relatively long life time. The proposed sensor revealed good selectivities over a wide variety of other cations include hard and soft metals. This electrode could be used in a pH range of 4.5-7.5. It was used as an indicator electrode in potentiometric titration of manganese(II) ions with EDTA solution.     

The petentiometric determination of peroxide hydrogen and glucose on the glassy electrode modified by the calix[4]arene

A new petentiometric method to determine peroxide hydrogen and glucose had been studied. This method had been applied on the petentiometric determination of peroxide hydrogen and glucose in the total ionic strength adjustment buffer (TISAB) (pH 7.5) solution with the glassy electrode modified by the calix[4]arene. The glassy carbon electrode covered with the calix[4]arene depended on the H₂O₂ concentration in the range of log[H₂O₂] from −3.3 to −1.2 in the solution of TISAB (pH 7.5) with nearly Nernstian slope of about 65.6 ± 3 mV and the detection limit of peroxide hydrogen was 4.0 × 10⁻⁵ mol L⁻¹. The glassy carbon electrode covered with the calix[4]arene depended on the glucose concentration in the range of log[glucose] from −3.6 to −2.8 in the solution of TISAB (pH 7.5) with nearly Nernstian slope of about 50.2 ± 2 mV and the detection limit of glucose was 2.0 × 10⁻⁵ mol L⁻¹. The electrode had the good selectivity, sensitivity, stability and repeatability.     

Determination of traces of cobalt in the presence of nioxime and cetyltrimethylammonium bromide by adsorptive stripping voltammetry

A sensitive method of Co(II) determination by adsorptive stripping voltammetry is presented. The method exploits the enhancement of cobalt peak current observed in the system Co(II)-nioxime-cetyltrimethylammonium bromide-piperazine-N,N′-bis(2-ethanesulfonic acid). The calibration plot for an accumulation time of 60 s is linear from 5 × 10⁻¹¹ to 3 × 10⁻⁹ mol L⁻¹. The relative standard deviation is 3.8% for Co(II) determination at concentration 1 × 10⁻⁹ mol L⁻¹. The detection limit is 1.7 × 10⁻¹¹ mol L⁻¹. The validation of the method is performed by the analyses of certified reference materials and comparing the result of Co(II) determination in river water sample by the proposed method with those obtained by ET AAS. The main advantage of this new system is the micro-trace Co(II) determination by adsorptive stripping voltammetry, as compared to those described before, a low concentration of the supporting electrolyte used, and so commercially available reagents without additional purification can be used.     

Electroanalytical determination of estriol hormone using a boron-doped diamond electrode

A boron-doped diamond (BDD) electrode was used for the electroanalytical determination of estriol hormone in a pharmaceutical product and a urine sample taken during pregnancy by square-wave voltammetry. The optimized experimental conditions were: (1) a supporting electrolyte solution of NaOH at a pH of 12.0, and (2) a frequency of 20 Hz, a pulse height of 30 mV and a scan increment of 2 mV (for the square-wave parameters). The analytical curve was linear in the concentration range of 2.0 × 10⁻⁷ to 2.0 × 10⁻⁵ mol L⁻¹ (r = 0.9994), with a detection limit of 1.7 × 10⁻⁷ mol L⁻¹ and quantification limit of 8.5 × 10⁻⁷ mol L⁻¹. Recoveries of estriol were in the range of 98.6-101.0%, for the pharmaceutical sample, and 100.2-103.4% for the urine sample, indicating no significant matrix interference effects on the analytical results. The accuracy of the electroanalytical methodology proposed was compared to that of the radioimmunoassay method. The values for the relative error between the proposed and standard methods were −7.29% for the determination of estriol in the commercial product and −4.98% in a urine sample taken during pregnancy. The results obtained suggest a reliable and interesting alternative method for electroanalytical determination of estriol in pharmaceutical products and urine samples taken during pregnancy using a boron-doped diamond electrode.     

Tris(2,2'-bipyridyl)ruthenium(II)-Zirconia-Nafion composite modified electrode applied as solid-state electrochemiluminescence detector on electrophoretic microchip for detection of pharmaceuticals of tramadol, lidocaine and ofloxacin

Tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺)-Zirconia-Nafion composite modified glassy carbon disk electrode as a solid-state electrochemiluminescence (ECL) detector is successfully applied to an electrophoretic microchip system with a wall-jet configuration. Pharmaceuticals such as tramadol, lidocaine and ofloxacin were selected to characterize the performance of this microchip capillary electrophoresis (CE)-ECL detection system. Voltammetric and ECL behaviors of immobilized Ru(bpy)₃²⁺ were investigated in lidocaine system. Influences of the separation electric field to cyclic voltammograms (CVs) of the immobilized Ru(bpy)₃²⁺ were also investigated. Tramadol, lidocaine and ofloxacin can be baseline separated without any additives. The detection limits (S/N = 3) were 2.5 × 10⁻⁵ mol L⁻¹ for tramadol, 5.0 × 10⁻⁶ mol L⁻¹ for lidocaine, 1.0 × 10⁻⁵ mol L⁻¹ for ofloxacin under the sample injection of picoliters, and the linear ranges were from 5.0 × 10⁻⁵ to 2.5 × 10⁻³ mol L⁻¹ for tramadol, 1.0 × 10⁻⁵ to 1.0 × 10⁻³ mol L⁻¹ for lidocaine, and 1.0 × 10⁻⁵ to 2.5 × 10⁻³ mol L⁻¹ for ofloxacin, respectively.     

Quantification of N-acetylcysteine in pharmaceuticals using cobalt phthalocyanine modified graphite electrodes

Flow injection analysis (FIA) with amperometric detection was employed for the quantification of N-acetylcysteine (NAC) in pharmaceutical formulations, utilizing an ordinary pyrolytic graphite (OPG) electrode modified with cobalt phthalocyanine (CoPc). Cyclic voltammetry was used in preliminary studies to establish the best conditions for NAC analysis. In FIA-amperometric experiments the OPG-CoPc electrode exhibited sharp and reproducible current peaks over a wide linear working range (5.0 × 10⁻⁵-1.0 × 10⁻³ mol L⁻¹) in 0.1 mol L⁻¹ NaOH solution. High sensitivity (130 mA mol⁻¹ cm²) and a low detection limit (9.0 × 10⁻⁷ mol L⁻¹) were achieved using the sensor. The repeatability (R.S.D.%) for 13 successive flow injections of a solution containing 5.0 × 10⁻⁴ mol L⁻¹ NAC was 1.1%. The new procedure was applied in analyses of commercial pharmaceutical products and the results were in excellent agreement with those obtained using the official titrimetric method. The proposed amperometric method is highly suitable for quality control analyses of NAC in pharmaceuticals since it is rapid, precise and requires much less work than the recommended titrimetric method.     

A SO2-selective electrode based on a Zn-porphyrin for wine analysis

This work describes the assessment of a SO₂-selective electrode based on the use of the neutral carrier 5,10,15,20-tetraphenyl(porphyrinate)zinc(II) in a PVC membrane plasticized with 2-nitrophenyl phenyl ether. After being conditioned in 2 mol L⁻¹ diethylamine solution for 24 h, the electrode exhibited selective anionic response toward the analyte in a concentration interval of more than four decades, with an slope of −59.5 mV dec⁻¹, a practical detection limit of 3.7 × 10⁻⁶ mol L⁻¹ and a low limit of linear range of 7.2 × 10⁻⁶ mol L⁻¹. The response mechanism is based on the displacement of the diethylamine:metalloporphyrin complex equilibrium within membrane bulk, inducing a variation in the cationic-sites to ionophore ratio. In turn, free hydroxyl ions are complexed by the displaced ionophore in a ratio 1:1 and translated as single negative charge nernstian response. Finally, the selectivity of the electrode is evaluated in view of its application to wine analysis. Results had high accuracy and precision when compared with a reference method.     

Amperometric quantification of sodium metabisulfite in pharmaceutical formulations utilizing tetraruthenated porphyrin film modified electrodes and batch injection analysis

The performance of a glassy carbon electrode modified with a porphyrin film formed by the [Co(TPyP){Ru(bipy)₂Cl}₄](TFMS)₅·H₂O complex for the analysis of sodium metabisulfite in pharmaceuticals is described. The sensor can be rapidly and easily prepared by drop-casting of a microliter volume of a diluted methanolic solution of the complex onto the electrode surface. The modified electrode with a supramolecular cobalt porphyrin film led to more favorable responses than the bare electrode. This can be ascribed to the much faster electron transfer processes to the analyte mediated by the tetraruthenated porphyrin and to the protection of the electrode against fouling. The association of the amperometric sensor with the batch injection analysis technique led to results that combine good repeatability of the current responses (relative standard deviation of 0.94% for 30 measurements), wide linear dynamic range (2.5 × 10⁻⁷ mol L⁻¹ to 5.0 × 10⁻⁴ mol L⁻¹), high sensitivity and low limits of detection (8.1 × 10⁻⁸ mol L⁻¹) and quantification (2.7 × 10⁻⁷ mol L⁻¹). The system was successfully applied to sodium metabisulfite quantification in commercial samples of injection formulations of sodium (or potassium) diclofenac. The results compared well with those obtained by the polarographic method.     

Rosmarinic acid determination using biomimetic sensor based on purple acid phosphatase mimetic

A new heterodinuclear Fe(III)Zn(II) complex which mimics the active site of the hydrolytic enzyme red kidney bean purple acid phosphatase was synthesized and characterized by IR, CHN and X-ray crystallographic analyses. This complex, [Fe^IIIZn^II(μ-OH)bpbpmp-CH₃](ClO₄)₂, containing the ligand (H₂bpbpmp-CH₃ = {2-[bis(2-pyridylmethyl)aminomethyl]-6-[(2-hydroxy-5-methylbenzyl) (2-pyridyl-methyl) aminomethyl]-4-methyl-phenol}) was employed in the construction of a biomimetic sensor and used in the determination of rosmarinic acid in plant extract samples. The response parameters and optimization of the biomimetic sensor design were evaluated. The best performance of this sensor was obtained for 75:15:10% (w/w/w) of the graphite powder:nujol:Fe(III)Zn(II) complex, 0.1 mol L⁻¹ phosphate buffer solution (pH 7.5), 1.19 × 10⁻⁴ mol L⁻¹ hydrogen peroxide with frequency, pulse amplitude, and scan increment at 30 Hz, 100 mV, and 0.6 mV, respectively. The rosmarinic acid concentration was linear in the range of 2.98 × 10⁻⁵ to 3.83 × 10⁻⁴ mol L⁻¹ (r = 0.9991) with a detection limit of 2.30 × 10⁻⁶ mol L⁻¹. This biomimetic sensor demonstrated long-term stability (300 days; 900 determinations) and reproducibility, with a relative standard deviation of 12.0%. The recovery study of rosmarinic acid in plant extract samples gave values from 90.3 to 98.3% and the concentrations determined showed agreement when compared with those obtained using capillary electrophoresis at the 95% confidence level.     

Voltammetry determination of trace manganese with pretreatment glassy carbon electrode by linear sweep voltammetry

This paper described the determination of trace manganese using linear sweep voltammetry at a pretreatment glassy carbon electrode. The glassy carbon electrode pretreated by electrochemical method in the 0.1 mol l⁻¹ NaOH solution greatly improved the electrode responsibility in the determination of manganese(II). The barrier to the detection of low manganese concentration was overcome by means of autocatalytic effect of manganese oxide deposited on the electrode in advance. Under the optimum experiments condition (0.04 mol l⁻¹ NH₃-NH₄Cl buffer solution, pH 9.0), the linear range was 4×10⁻⁸ to 1×l0⁻⁶ mol l⁻¹ Mn(II) for linear sweep voltammetry and 1×10⁻⁹ to 4×10⁻⁸ mol l⁻¹ Mn(II) for convolution voltammetry. The relative standard deviation for 2×10⁻⁸ mol l⁻¹ Mn(II) is 3.4%. The proposed method is simple, rapid, sensitive and selective. It had been applied to the determination of trace manganese in samples with satisfactory results.     

Zirconium ion selective electrode based on bis(diphenylphosphino) ferrocene incorporated in a poly(vinyl chloride) matrix

A novel potentiometric zirconium - PVC matrix membrane sensor incorporating bis(diphenylphosphino) ferrocene as an electroactive material and tris(2-ethylhexyl)phosphate as solvent mediator is described. In mixed acetate buffer solution of pH 4.8, the sensor displays a rapid and linear response for zirconium ion over the concentration range 1.0 × 10⁻¹ to 1.0 × 10⁻⁷ mol L⁻¹ with a good slope of 59.7 ± 0.3 mV per decade and detection limit 1.8 × 10⁻⁸ mol L⁻¹. The best performance was obtained with membrane composition 33% PVC, 65% TEHP, 1% NaTPB and 1% ionophore. The proposed electrode revealed excellent selectivity for zirconium ion over a wide variety of alkali, alkaline earth, transition and heavy metal ions and could be used in a pH range of 4.15-7.8. The electrode was applied for at least 1 month without any considerable divergence in the potential responses. The practical utility of the electrode has been demonstrated by its use as an indicator electrode in the potentiometric titration of zirconium ions with sodium fluoride and in determination of zirconium ion in some alloy, tape and waste water samples.     

Determination of trace thiocyanate with nano-silver coated multi-walled carbon nanotubes modified glassy carbon electrode

Novel nano-silver coated multi-walled carbon nanotube composites were prepared and used to fabricate a modified electrode. The application of the nano-silver coated multi-walled carbon nanotube composites modified electrode for determination of trace thiocyanate is demonstrated for the first time. The influence of substrate, pH and interference of coexisting substances was investigated for response properties of the electrode. There was a linear relationship at the range 2.5 × 10⁻⁹ to 5 × 10⁻⁸ mol L⁻¹ and 5 × 10⁻⁸ to 1 × 10⁻⁶ mol L⁻¹ of thiocyanate with the decrement of anodic DPV peak currents. The limit of detection was 1 × 10⁻⁹ mol L⁻¹(S/N = 3). The constructed electrode showed excellent reproducibility and stability. Actual urine and saliva samples of smoker and non-smoker were analyzed and satisfactory results were obtained. This method provides a new way to construct any electrode for biological and environmental analysis.