Voltammetric behavior and quantitative determination of ambazone concentrations in urine and in a pharmaceutical formulation

The use of square wave adsorptive stripping voltammetry (SWAdSV) in conjunction with a cyclic renewable silver amalgam film electrode (Hg(Ag)FE) for the analytical determination of ambazone in urine samples and pharmaceutical formulations is described. A single reduction peak in Britton-Robinson buffer at pH 4.0 was detected at about ?1.4 V versus Ag/AgCl. Mechanistic studies have shown that the compound can act as an electrocatalyst. The method was validated. The analytical curve was linear in the concentration range from 1.0×10^?9 to 1.0×10^?7 mol L^?1. The detection and quantification limits were found to be 3.0×10^?10 mol L^?1 and 1.0×10^?9 mol L^?1, respectively. The proposed method was successfully applied to ambazone determination in real samples.      

Electrochemical determination of tyrosine in the presence of uric acid at a carbon paste electrode modified with multi-walled carbon nanotubes enhanced by sodium dodecyl sulfate

Tyrosine (Tyr) was quantitated with high sensitivity and selectivity in the presence of uric acid (UA) using a carbon paste electrode modified with multi-walled carbon nanotubes. Tyr and UA were catalytically oxidized with diffusion-controlled characteristics. They were determined simultaneously by differential pulse voltammetry with a potential difference of 350 mV. The electrocatalytic currents increase linearly with Tyr and UA concentrations 4×10^?7?1×10^?4 M and 3×10^?7?2×10^?4 M. Their detection limits were 1×10^?7 and 5.1×10^?8 M respectively. In the presence of sodium dodecyl sulfate the Tyr detection limit improved from 1×10^?7 to 6.9×10^?8 M. The electrode was successfully used to quantitate Tyr and UA in serum.      

Development of a nanocomposite system and its application in biosensors construction

The present work describes the development of a nanocomposite system and its application in construction of a new amperometric biosensor applied in the determination of total polyphenolic content from propolis extracts. The nanocomposite system was based on covalent immobilization of laccase on functionalized indium tin oxide nanoparticles and it was morphologically and structural characterized. The casting of the developed nanocomposite system on the surface of a screen-printed electrode was used for biosensor fabrication. The analytical performance characteristics of the settled biosensor were determined for rosmarinic acid, caffeic acid and catechol (as laccase specific substrate). The linearity was obtained in the range of 1.06×10^?6 ? 1.50×10^?5 mol L^?1 for rosmarinic acid, 1.90×10^?7 ? 2.80×10^?6 mol L^?1 for caffeic acid and 1.66×10^?6 ? 7.00×10^?6 mol L^?1 for catechol. A good sensitivity of amperometric biosensor 141.15 nA µmol^?1 L^?1 and fair detection limit 7.08×10^?8 mol L^?1 were obtained for caffeic acid. The results obtained for polyphenolic content of propolis extracts were compared with the chromatographic data obtained by liquid-chromatography with diode array detection.      

Flow-injection spectrophotometric determination of dipyrone in pharmaceutical formulations using a solid-phase reactor with copper(II) phosphate

In this work, a flow-injection spectrophotometric method for dipyrone determination in pharmaceutical formulations was developed. Dipyrone sample solutions were injected into a carrier stream of deionized water and the reaction was carried out in a solid-phase reactor (12 cm, 2.0 mm i.d.) packed with Cu₃(PO₄)_2(s) entrapped in a matrix of polyester resin. The Cu(II) ions were released from the solid phase reactor by the formation of Cu(II)-(dipyrone)_n complex. When the complex is released, it reacts with 0.02% m/v alizarin red S in deionized water to produce a Cu(VABO₃)₃ complex whose absorbance was monitored at 540 nm. The calibration graph was linear over the range 5.0×10^?5–4.0×10^?4 mol L^?1 with a detection limit of 2.0×10^?5 mol L^?1 and relative standard deviation for 10 successive determinations of 1.5% (2.0×10^?4 mol L^?1 dipyrone solution). The calculated sample throughput was 60 h^?1. The column was stable for at least 8 h of continuous use (500 injections) at 25°C. Pharmaceutical formulations were analyzed and the results from an official procedure measurement were compared with those from the proposed FIA method in order to validate the latter method.      

Voltammetric detection of guanosine and adenosine using a carbon paste electrode modified with 1-ethyl-3-methylimidazolium ethylsulfate

A novel kind of carbon paste electrode (CPE) was prepared by mixing graphite powder, liquid paraffin and the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate. The resulting electrode was used for the simultaneous determination of guanosine and adenosine by differential pulse voltammetry. Compared to a conventional CPE, the oxidation peak currents are largely increased, and the oxidation peak potentials are negatively shifted. The electrochemical responses to guanosine and adenosine were investigated. Under optimized conditions, the calibration curves are linear in the concentration range from 1.0?×?10^-6?mol?L^-1 to 1.6?×?10^-4?mol?L^-1 for guanosine, and from 1.0?×?10^-6?mol?L^-1 to 2.7?×?10^-4?mol?L^-1 for adenosine at pH 3.5. Substances potentially interfering in the biological matrix do no interfere. The method was successfully applied to detect adenosine and guanosine in human urine without sample treatments.

The electrochemistry of uric acid at a gold electrode modified with L-cysteine, and its application to sensing uric urine

The electrochemistry of uric acid at a gold electrode modified with a self-assembled film of L-cysteine was studied by cyclic voltammetry and differential pulse voltammetry. Compared to the bare gold electrode, uric acid showed better electrochemical response in that the anodic peak current is stronger and the peak potential is negatively shifted by about 100 mV. The effects of experimental conditions on the oxidation of uric acid were tested and a calibration plot was established. The differential pulse response to uric acid is linear in the concentration range from 1.0?×?10^?6 to ~?1.0?×?10^?4 mol?L^?1 (r?=?0.9995) and from 1.0?×?10^?4 to ~?5.0?×?10^?4 mol?L^?1 (r?=?0.9990), the detection limit being 1.0?×?10^?7 mol?L^?1 (at S/N?=?3). The high sensitivity and good selectivity of the electrode was demonstrated by its practical application to the determination of uric acid in urine samples.

Bismuth and Bismuth-Chitosan modified electrodes for determination of two synthetic food colorants by net analyte signal standard addition method

In this paper, an electrochemical application of bismuth film modified glassy carbon electrode for azo-colorants determination was investigated. Bismuth-film electrode (BiFE) was prepared by ex-situ depositing of bismuth onto glassy carbon electrode. The plating potential was ?0.78 V (vs. SCE) in a solution of 0.15 mg mL^?1 Bi(III) and 0.05 mg mL^?1 KBr for 180 s. In the next step, a thin film of chitosan was deposited on the surface of bismuth modified glassy carbon electrode, thus the bismuth-chitosan thin film modified glassy carbon electrode (Bi-CHIT/GCE) was fabricated and compared with bare GCE and bismuth modified GCE. Azo-colorants such as Sunset Yellow and Carmoisine were determined on these electrodes by differential pulse voltammetry. Due to overlapping peaks of Sunset Yellow and Carmoisine, simultaneous determination of them is not possible, so net analyte signal standard addition method (NASSAM) was used for this determination. The results showed that coated chitosan can enhance the bismuth film sensitivity, improve the mechanical stability without caused contamination of surface electrode. The Bi-CHIT/GC electrode behaved linearly to Sunset Yellow and Carmoisine in the concentration range of 5×10^?6 to 2.38×10^?4 M and 1×10^?6 to 0.41×10^?4 M with a detection limit of 10 µM (4.52 µg mL^?1) and 10 µM (5.47 µg mL^?1), respectively      

Determination of lead(II) in aqueous solution using carbon nanotubes paste electrodes modified with Amberlite IR-120

A new composite electrode is described for anodic stripping voltammetry determination of Pb(II) at trace level in aqueous solution. The electrode is based on the use of multiwalled carbon nanotubes and Amberlite IR-120. The anodic stripping voltammograms depend, to a large extent, on the composition of the modified electrode and the preconcentration conditions. Under optimum conditions, the anodic peak current at around ?0.57 V is linearly related to the concentration of Pb(II) in the range from 9.6?×?10^?8 to 1.7?×?10^?6 mol L^?1 (R?=?0.998). The detection limit is 2.1?×?10^?8 mol L^?1, and the relative standard deviation (RSD) at 0.24?×?10^?6 mol L^?1 is 1.7% (n?=?6). The modified electrode was applied to the determination of Pb(II) using the standard addition method; the results showed average relative recoveries of 95% for the samples analysed.

Spectrophotometric study of competitive complexation equilibria involving overlapped spectral responding species: Determination of the stability constant of bismuth-pyrophosphate complex

Spectrophotometric study of competitive complex formation equilibria involving overlapped spectral responding species applying a simple and versatile algorithm was carried out. The algorithm involves multivariable regression for calculation of equilibrium concentrations from multiwavelength data and mass action law for the stability constant calculation. The used regression functions are part of common statistical software. Stability constants and complex stoichiometry of competing equilibria were simultaneously determined. The species concentration profiles at several spectral overlapping and ??-coefficient of competing reaction were obtained. Non-absorbing bismuth ?? pyrophosphate (PPh) system was studied as a competitive reaction of bismuth ?? 4-(2-Pyridylazo) resorcinol (PAR) complex. The formation of Bi-PPh complex with 1:1 stoichiometry was proved in the studied concentration region (C_Bi = 1×10^?5 mol L^?1; C_PPh = 5×10^?6 ? 1×10^?4 mol L^?1). The stability constant of the complex at pH 1 and ?? = 1.0 have been determined: log?? = 4.2±0.2.      

Voltammetric quantitation at the mercury electrode of the anticholinergic drug flavoxate hydrochloride in bulk and in a pharmaceutical formulation

Flavoxate hydrochloride, 2-piperidinoethyl 3-methyl-4-oxo-2-phenyl-4-H-chromene-8-carboxylate, is a smooth muscle antispasmodic. Its electrochemical behavior was studied at the mercury electrode in buffered solutions containing 30% (v/v) methanol using dc-polarography, differential-pulse polarography, cyclic voltammetry, and linear sweep-and square-wave adsorptive stripping voltammetry. Sensitive and precise procedures were developed for determination of bulk flavoxate hydrochloride and in the pharmaceutical formulation Genurin® S.F, without sample pretreatment or extraction. Limits of quantitation (LOQ) of 1 × 10^?5, 5 × 10^?6, 1 × 10^?8 and 1 × 10^?9 M flavoxate hydrochloride were achieved by dc-polarography, differential-pulse polarography, linear sweep and square-wave adsorptive stripping voltammetric, respectively.      

Voltammetric behavior of rutin at a boron-doped diamond electrode. Its electroanalytical determination in a pharmaceutical formulation

This paper examined for the first time, the possibilities of the usage of a boron-doped diamond electrode for the redox behavior of rutin using cyclic and adsorptive stripping voltammetry. The cyclic voltammograms showed a pair of redox peaks at lower potentials followed by an irreversible oxidation peak at higher positive potential. Using square-wave adsorptive stripping voltammetry, the compound yielded a well-defined voltammetric response in Britton-Robinson buffer, pH 4.0 at +0.48 V (vs. Ag/AgCl) (after 60 s accumulations at a fixed potential of 0.2 V). The calibration curve was linear in the concentration range from 0.01 µg mL^?1 to 0.1 µg mL^?1 (1.64×10^?8 M ? 1.64×10^?7 M). A detection limit of 0.0017 µg mL^?1 (2.78×10^?9 M) was observed without any chemical modifications and electrochemical surface pretreatments. As an example, the practical applicability of boron-doped diamond electrode was tested with the measurement of rutin in dietary supplement products.      

Sensitive determination of ATP using a carbon paste electrode modified with a carboxyl functionalized ionic liquid

We report on a new electrode for the determination of adenosine-5??-triphosphate (ATP). It is based on modified carbon paste electrode that contains an ionic liquid (IL) as the binder. The electrode shows strong electrocatalytic oxidative activity towards ATP at pH 4.5 in giving a well-defined single oxidation peak. The oxidation reaction is adsorption-controlled and due to the presence of the highly conductive IL. The electron transfer rate constant was calculated to be 2.04×10^?C3 s^?C1, and the surface coverage is 1.11×10^?C10 mol cm^?C2. Under the selected conditions, the oxidation peak current changes linearly with the concentration of ATP in the range from 5.0 to 1000???mol L^?1 and a detection limit of 1.67???mol L^?1 (3???) as determined by differential pulse voltammetry. The method displays good selectivity and was applied to the determination of ATP injection samples with satisfactory results.

Pulse perturbation technique for determination of piroxicam in pharmaceuticals using an oscillatory reaction system

A simple and reliable novel kinetic method for the determination of piroxicam (PX) was proposed and validated. For quantitative determination of PX, the Bray-Liebhafsky (BL) oscillatory reaction was used in a stable non-equilibrium stationary state close to the bifurcation point. Under the optimized reaction conditions (T = 55.0°C, [H₂SO₄]₀ = 7.60×10^?2 mol L^?1, [KIO₃]₀ = 5.90×10^?2 mol L^?1, [H₂O₂]₀ = 1.50×10^?1 mol L^?1 and j ₀ = 2.95×10^?2 min^?1), the linear relationship between maximal potential shift ΔE _m , and PX concentration was obtained in the concentration range 11.2–480.5 μg mL^?1 with a detection limit of 9.9 μg mL^?1. The method had a rather good sample throughput of 25 samples h^?1 with a precision RSD = 4.7% as well as recoveries RCV ≤ 104.4%. Applicability of the proposed method to the direct determination of piroxicam in different pharmaceutical formulations (tablets, ampoules and gel) was demonstrated.      

Electrochemical determination of paraquat using a DNA-modified carbon ionic liquid electrode

Deoxyribonucleic acid (DNA) was electrochemically deposited on a carbon ionic liquid electrode to give a biosensor with excellent redox activity towards paraquat as shown by cyclic voltammetry and differential pulse voltammetry. Experimental conditions were optimized with respect to sensing paraquat by varying the electrochemical parameters, solution pH, and accumulation time of DNA. Under the optimized conditions, a linear relation exists between the reduction peak current and the concentration of paraquat in the range from 5?×?10^?8 mol L^?1 to 7?×?10^?5 mol L^?1, with a detection limit of 3.6?×?10^?9 mol L^?1. The utility of the method is illustrated by successful analysis of paraquat in spiked real water samples.

LC-ED with an Acetylene Black–Dihexadecyl Hydrogen Phosphate Composite Film-Modified Electrode for in Vivo Analysis of Thiols in Rat Striatal Microdialysate

Liquid chromatography with electrochemical detection (LC-ED), coupled with in vivo microdialysis sampling, has been used for analysis of thiols. An acetylene black–dihexadecyl hydrogen phosphate (AB–DHP) composite film-modified electrode was used as working electrode. The AB–DHP-modified electrode enabled efficient electrocatalytic oxidation of l-cysteine (l-Cys) and glutathione (GSH) with relatively high sensitivity, stability, and longevity. The peak currents of l-Cys and GSH were linear in the concentrations ranges 2.0 × 10^?7–2.0 × 10^?4 and 3.0 × 10^?7–5.0 × 10^?4 mol L^?1, respectively, with calculated detection limits (S/N = 3) of 1.0 × 10^?7 and 2.0 × 10^?7 mol L^?1, respectively. The method has been successfully used to measure the amounts of l-Cys and GSH in striatal microdialysate of freely moving rats.     

A low-cost automated flow analyzer based on low temperature co-fired ceramic and LED photometer for ascorbic acid determination

An automated flow analyzer based on low temperature co-fired ceramic (LTCC), a solid-phase reactor (SPR) and a low-cost photometer was designed for ascorbic acid (AA) determination in pharmaceutical formulations. It consists of a peristaltic pump, three-way solenoid valves, SPR to chemically convert Cu(II) into Cu(I), and a LTCC device for mixing the liberated copper with bathocuproine and detection. The flow cell in the LTCC employed an ultrabright LED — photodiode photometer. The analyzer successfully determined AA in pharmaceutical formulations. The analytical curve from 8.5×10^?6 to 7.0×10^?4 M gave a detection limit of 7.0×10^?7 M and a RSD of 2.1% for a 2.0×10^?4 M AA solution (n = 10). A high sampling frequency of 102 h^?1 and low reagent and sample consumption (150 µL) resulted.      

Anodic stripping voltammetric determination of silver ion at a carbon paste electrode modified with carbon nanotubes

A carbon paste electrode (CPE) was modified with multi-wall carbon nanotubes and successfully applied to the determination of silver ion by differential pulse anodic stripping voltammetry. Compared to a conventional CPE, a remarkably improved peak current response and sensitivity is observed. The analytical procedure consisted of an open circuit accumulation step for 2?min in ?0.4?V, this followed by an anodic potential scan between +0.2 and?+?0.6?V to obtain the voltammetric peak. The oxidation peak current is proportional to the concentration of silver ion in the range from 1.0?×?10^?8 to 1.0?×?10^?5?mol?L^?1, with a detection limit of 1.8?×?10^?9?mol?L^?1 after an accumulation time of 120?s. The relative standard deviation for 7 successive determinations of Ag(I) at 0.1???M concentration is 1.99%. The procedure was validated by determining Ag(I) in natural waters.

Enantioselective recognition of penicillamine enantiomers on bovine serum albumin-modified glassy carbon electrode

As a natural chiral selector, bovine serum albumin (BSA) has been used to recognize penicillamine (Pen) enantiomers through electrochemical methods. The recognition and assay rely on the stereoselectivity of BSA embedded in ultrathin Al₂O₃ sol–gel film coated on the surface of glassy carbon electrode (BSA/GCE). The enantioselective interaction between Pen enantiomers and BSA was monitored by cyclic voltammetry and electrochemical impedance spectroscopy measurements, from which larger response signals were obtained from d-Pen. The factors influencing the performance of the modified biosensor were also investigated. The association constant (K) was calculated to be 1.93?×?10⁴?L?mol^?1 for d-Pen and 1.20?×?10³?L?mol^?1 for l-Pen. A good linear response was exhibited with the concentration of Pen enantiomers by BSA/GCE over the range of 1?×?10^?8–1?×?10^?1?mol?L^?1 with a detection limit of 3.31?×?10^?9?mol?L^?1.     

Sensitive and fast determination of papaverine by adsorptive stripping voltammetry on renewable mercury film electrode

The renewable mercury film electrode, applied for the determination of papaverine traces using differential pulse adsorptive stripping voltammetry (DP AdSV) is presented. The calibration graph obtained for papaverine is linear from 1.25 nM (0.42 µg L^?1) to 95 nM (32.2 µg L^?1) for a preconcentration time of 60 s, with correlation coefficient of 0.998. For the renewable mercury electrode (Hg(Ag)FE) with a surface area of 9.1 mm² the detection limit for a preconcentration time of 60 s is 0.7 nM (0.24 µg L^?1). The repeatability of the method at a concentration level of the analyte as low as 17 µg L^?1, expressed as RSD is 3.3% (n=5). The proposed method was successfully applied and validated by studying the recovery of papaverine from drugs, urine and synthetic solution.      

Cobalt(II) ion-selective electrode with solid contact

A new all plastic sensor for Co²⁺ ions based on 2-amino-5 (hydroxynaphtyloazo-1′)-1,3,4 thiadiazole (ATIDAN) as ionophore was prepared. The electrode exhibits a low detection limit of 1.5 × 10⁻⁶ mol L⁻¹ and almost theoretical Nernstian slope in the activity range 4.0 × 10⁻⁶–1 × 10⁻¹ mol L⁻¹ of cobalt ions. The response time of the sensor is less than 10 s and it can be used over a period of 6 months without any measurable divergence in potential. The proposed sensor shows a fairly good selectivity for Co(II) over other metal ions. The electrode was successfully applied for determination of Co²⁺ in real samples and as an indicator electrode in potentiometric titration of Co²⁺ ions with EDTA.