Use of a Boron-Doped Diamond Electrode for Amperometric Assay of Bromide and Iodide Ions

The electrochemical assay of bromide and iodide ions at boron-doped diamond (BDD) electrode was investigated by cyclic voltammetry (CV) and chronoamperometry (CA). Comparison experiments were carried out using a glassy carbon (GC) electrode. The BDD electrode exhibited well-resolved and irreversible reduction voltammograms, while the GC electrode provided only an ill-defined response. Cyclic voltammetric signals at BDD electrode for 10 mM Br⁻ and I⁻ were observed at 561 and 125 mV vs. SCE; the values shifted negatively for 228.7 and 187.5 mV, respectively, compared to those at GC electrode. It was also found that the peak current of Br⁻ and I⁻ was in direct proportion to the scan rate, which is indicative of a surface confined reduction process. Sensitive amperometric responses for Br⁻ and I⁻ were obtained covering the linear ranges 0.666 μM–1 mM and 13.3 nM–1 mM, respectively, and their detection limits were 0.53 μM and 1.67 nM, respectively, under the optimum pH and applied potential. The amperometric response was very reproducible and stable with satisfactory recovery results. __________ From Zhurnal Analiticheskoi Khimii, Vol. 60, No. 11, 2005, pp. 1193–1199. Original English Text Copyright ? 2005 by Jing Wu, Xiaoli Li, Cunxi Lei, Xumei Wu, Guoli Shen, and Rugin Yu. This article was submitted by the authors in English.     

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.      

A Simple Approach to Simultaneous Electroanalytical Quantification of Acetaminophen and Tramadol Using a Boron‐doped Diamond Electrode in the Existence of Sodium Dodecyl Sulfate

The present work describes the individual, selective and simultaneous quantification of acetaminophen (ACP) and tramadol hydrochloride (TRA) using a modification‐free boron‐doped diamond (BDD) electrode. Cyclic voltammetric measurements revealed that the profile of the binary mixtures of ACP and TRA were manifested by two irreversible oxidation peaks at about +1.04 V (for ACP) and +1.61 V (for TRA) in Britton‐Robinson (BR) buffer pH 3.0. TRA oxidation peak was significantly improved in the presence of anionic surfactant, sodium dodecyl sulfate (SDS), while ACP signal did not change. By employing square‐wave stripping mode in BR buffer pH 3.0 containing 8×10^?4 mol L^?1 SDS after 30 s accumulation under open‐circuit voltage, the BDD electrode could be used for quantification of ACP and TRA simultaneously in the ranges 1.0–70 μg mL^?1 (6.6×10^?6–4.6×10^?4 mol L^?1) and 1.0–70 μg mL^?1 (3.3×10^?6–2.3×10^?4 mol L^?1), with detection limits of 0.11 μg mL^?1 (7.3×10^?7 mol L^?1) and 0.13 μg mL^?1 (4.3×10^?7 mol L^?1), respectively. The practical applicability of the proposed approach was tested for the individual and simultaneous quantification of ACP and/or TRA in the pharmaceutical dosage forms.     

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      

First Electroanalytical Methodology for the Determination of Hordenine in Dietary Supplements using a Boron‐doped Diamond Electrode

The present work describes the first electrochemical investigation and a simple, rapid and modification‐free electroanalytical methodology for quantification of hordenine (a potent phenylethylamine alkaloid) using a boron‐doped diamond electrode. At optimized square‐wave voltammetric parameters, the observed oxidation peak current in 0.1 M HClO₄ at +1.33 V (vs. Ag/AgCl) increased linearly from 5.0 to 100 μg mL^?1 (3.0×10^?5–6.1×10^?4 M), with detection limit of 1.3 μg mL^?1 (7.8×10^?6 M). The applicability of the developed method was tested with the determination of hordenine in the commercial dietary supplement formulations.     

Differential pulse polarographic behaviour of thiazopyr herbicide and application to its determination in fruit juice and soil samples

A differential pulse polarographic method for the determination of the herbicide thiazopyr has been developed. The polarographic study of thiazopyr exhibited two well-defined cathodic peaks within the pH range of 1.0 to 8.0. The variation of pH and polarographic parameters indicated that the optimum conditions under which thiazopyr could be reduced were a pH 7.0 BR buffer solution, a reduction peak potential of ?1270 mV (vs. SCE), scan rate of 5 mV s^?1, pulse amplitude of 50 mV with pulse duration of 50 ms at an ambient temperature of 25 ± 3°C. The main reduction peak was characterised by cyclic voltammetry as being irreversible and diffusion-controlled. A linear relationship between the peak current and the concentration of thiazopyr was obtained in the range of 0.43–38.6 µg mL^?1, with a detection limit of 0.127 µg mL^?1. The proposed method was successfully applied to the determination of thiazopyr in spiked fruit juice and soil samples. The mean recoveries of the 19.8 µg g^?1 and 3.96 µg mL^?1 thiazopyr spiked to soil and orange juice were 20.2 ± 1.0 µg g^?1 and 3.84 ± 0.12 µg mL^?1, at 95% confidence level, respectively. The sufficiently good recoveries and low relative standard deviation (RSD) data confirm the high accuracy and precision of the proposed method. The interferences effects of several commonly used pesticides and inorganic species were also studied. Interfering effects were eliminated either by providing selectivity with pH, or using EDTA as complexing agent.     

Synthesis,biological evaluation,quantitative-SAR and docking studies of novel chalcone derivatives as antibacterial and antioxidant agents

In the present study, a series of chalcone derivatives including 17 new compounds were synthesised; their antibacterial activities against eleven bacteria, and their free radical-scavenging activities using DPPH were evaluated. All compounds showed significant antibacterial activities against both Gram-positive and Gram-negative bacteria. In particular, compound IIIf strongly inhibited Staphylococcus aureus (JMC 2151) and Enterococcus faecalis (CARS 2011-012) with MIC values of 6.25 µg mL^?1 and 12.5 µg mL^?1, respectively, which are comparable to that of the standard antibiotic, nalidixic acid. Compound IIIg also inhibited S. aureus with a MIC value similar to that of nalidixic acid (6.25 µg mL^?1). Furthermore, like nalidixic acid (MIC value of 25 µg mL^?1), compounds IIIa, IIIc and IIId inhibited Listeria monocytogenes (ATCC 43256) with MIC values of 25 µg mL^?1, 12.5 µg mL^?1 and 25 µg mL^?1, respectively. Quantitative structure-activity relationship (Q-SAR) studies using physicochemical calculations indicated that the antibacterial activities of chalcone derivatives correlated well with predicted physicochemical parameters (logP and PSA). Docking simulation by positioning the most active compound IIIf in the active site of the penicillin-binding protein (PBP-1b) of S. aureus was performed to explore the feasible binding mode. Furthermore, most of the compounds synthesised exhibited significant DPPH radical-scavenging activity, although compounds IIc and IIIc exhibited the greatest antioxidant activity with IC₅₀ values of 1.68 µM and 1.44 µM, respectively, comparable to that of the standard antioxidant, ascorbic acid (1.03 µM).     

Improved Multianalyte Determination of the Intense Sweeteners Aspartame and Acesulfame‐K with a Solid Sensing Zone Implemented in an FIA Scheme

Abstract

A multianalyte flow‐through sensor is proposed for the simultaneous determination of aspartame (AS) and acesulfame‐K (AK) in tabletop sweeteners. The procedure is based on the transient retention of AK in the ion exchanger Sephadex DEAE A‐25 placed in the flow‐through cell of a monochannel flow injection analysis (FIA) set‐up using pH 2.70 ortophosphoric acid/sodium dihydrogen phosphate buffer 0.06 M as carrier. In these conditions AS is very weakly retained, which makes it possible to measure the intrinsic ultraviolet (UV) absorbance of first AS and then AK after desorption by the carrier itself. The applicable concentration range, the detection limit, and the relative standard deviation were the following: for AS, from 10 to 100 µg mL^?1; 5.65 µg mL^?1; 3.4% (at 50 µg mL^?1); and for AK, between 40 and 100 µg mL^?1; 11.9 µg mL^?1 and 1.61% (at 50 µg mL^?1). The method was applied and validated satisfactorily for the determination of AS and AK blends in tabletop sweeteners. The results were compared against an HPLC reference method.     

Renewable Silver‐Amalgam Film Electrode for Rapid Square‐Wave Voltammetric Determination of Thiamethoxam Insecticide in Selected Samples

The paper presents the use of a renewable silver‐amalgam film electrode (Hg(Ag)FE) for the determination of the insecticide thiamethoxam (TMO) in Britton‐Robinson buffer pH 7.0 (LOD=0.25 µg mL^?1, LOQ=0.70 µg mL^?1) by direct cathodic square‐wave voltammetry (SWV). The voltammetric response for TMO obtained at this electrode was the same as that obtained with a hanging mercury drop electrode, represented by two distinct reduction peaks. Since the electron transfer processes are coupled with chemical reactions involving protons, the SWV signals strongly depend on the pH of the supporting electrolyte. The developed Hg(Ag)FE‐SWV method was tested for the determination of TMO in spiked honey and river water samples, as well as for the determination of its content in the commercial formulation Actara 25 WG.     

Rapid Low-Cost Determination of Lead(II) in Cassava by an iPod-Based Digital Imaging Colorimeter

An iPod-based digital image colorimeter was developed for the determination of lead(II) in cassava. The method is based on the color values of a lead(II) solution following its reaction with dithizone. Lead(II) from cassava was extracted using an ultraviolet-digestion unit followed by the color-forming reaction and image capture using the ColorConc application operated on an iPod touch. The concentration was predicted by comparing the color values with those collected in a database. The time needed for complete digestion was 30?min. The determined concentrations of lead(II) were from 0.10 to 1.00?µg mL^?1. The limits of detection and quantitation were 0.0120 and 0.0399?µg mL^?1, respectively. The recovery values were 105?±?7.07% and 109?±?6.61% at 0.2?µg mL^?1 and 0.4?µg mL^?1 lead(II) (n?=?5). The reported method was demonstrated to be simple, accurate, rapid, precise, and low cost.     

Self‐Assembled Monolayers of Cucurbit[6]uril on a Gold Electrode for 4,4′‐Oxydianiline Determination. Analytical Application

Self‐assembled monolayers of cucurbit[6]uril (CB[6]) on a gold electrode have been used for 4,4′‐oxydialine (ODA) analysis. The formation of the supramolecular complex between ODA and CB[6] was used for the molecular selection and the electroanalytical determination of this analyte. In addition to this, all the parameters affecting the modification of the gold electrode and the determination of 4,4′‐oxydianiline were optimized by square wave voltammetry. Upon the electrode modification, pentanethiol was employed to fill up the exposed surface between CB[6] molecules. The calculated detection and determination limits were 0.06 µg mL^?1 and 0.19 µg mL^?1, respectively, with good accuracy and precision as shown by the calculated values for the relative error and relative standard deviation (E_r=0.1 % and RDS=2.9 %; n=10 ). Moreover, the developed methodology was successfully applied to the 4,4′‐oxydialine determination in real wastewaters and shoe‐dyeing samples.     

Simultaneous and Direct Determination of Tryptophan and Tyrosine at Boron‐Doped Diamond Electrode

A facile method for the simultaneous measurement of tryptophan (Trp) and tyrosine (Tyr) was firstly exploited at unmodified boron‐doped diamond (BDD) electrode. The experimental results indicated that by using differential pulse voltammetry, the oxidative peaks of these two kinds of amino acids could be completely separated at BDD electrode. The peak separation of Trp and Tyr was developed to be 0.64 V when Na₂PO₄/NaOH buffer solution with the optimized pH 11.2 was employed. The detection limit of Trp was obtained to be 1×10^?5 M, while that of Tyr was achieved to be 1×10^?6 M. The present method was also evidenced to be available to the determination of real samples of amino acids.     

Simultaneous Differential Pulse Voltammetric Determination of Sulfamethoxazole and Trimethoprim on a Boron‐Doped Diamond Electrode

The performance of hydrogen‐ (HT) and oxygen‐terminated (OT) boron‐doped diamond (BDD) electrodes (electrochemically pretreated) on the simultaneous differential pulse voltammetric determination of sulfamethoxazole and trimethoprim in pharmaceutical products is presented. Under the optimum analytical experimental conditions, the HT‐BDD electrode presented two well‐defined oxidation peaks at 920 and 1100 mV vs. Ag/AgCl for sulfamethoxazole and trimethoprim, respectively. On the other hand, when the OT‐BDD electrode was used, the sulfamethoxazole oxidation current peak was decreased twenty fold. The calculated LOD values for sulfamethoxazole and trimethoprim using the HT‐BDD electrode were 3.65 μg L^?1 and 3.92 μg L^?1, respectively. The results obtained in the simultaneous determination of sulfamethoxazole and trimethoprim in three different commercial formulations were similar to those obtained using a standard HPLC method at 95% confidence level.     

Nonextractive Trace Level Simultaneous Determination of Mercury(II) and Zinc(II) in Environmental Samples with 2‐(5‐Bromo‐2‐pyridylazo)‐5‐diethylaminophenol and Cetylpyridinium Chloride

Abstract

A simple, rapid, selective, and sensitive method for the derivative spectrophotometric determination of Hg(II) and its simultaneous determination in the presence of Zn(II) using 2‐(5‐bromo‐2‐pyridylazo)‐5‐diethylaminophenol in the presence of cetylpyridinium chloride, a cationic surfactant, has been developed. The molar absorption coefficient and analytical sensitivity of the 1∶1 Hg(II) complex at 558 nm (λ_max) are 5.78×10⁴ L mol^?1 cm^?1 and 0.67 ng mL^?1, respectively. The detection limit of Hg(II) is 1.40×10^?2 ng mL^?1, and Beer's law is valid in the concentration range 0.05–2.40 µg mL^?1. Overlapping spectral profiles of Hg(II) and Zn(II) complexes in zero‐order mode interfere in their simultaneous determination. However, 0.10–2.00 µg mL^?1 of Hg(II) and 0.065–0.650 µg mL^?1 of Zn(II), when present together, can be simultaneously determined at zero cross point of the derivative spectrum, without any prior separation. The relative standard deviation for six replicate measurements of solutions containing 0.134 µg mL^?1 of Hg(II) and 0.620 µg mL^?1 of Zn(II) is 1.72 and 1.47%, respectively. The proposed method has successfully been evaluated for trace level simultaneous determination of Hg(II) and Zn(II) in environmental samples.     

A novel vortex-assisted liquid phase microextraction method for parabens in cosmetic oil products using deep eutectic solvent

ABSTRACT

The parabens, which are harmful to our bodies, are primarily utilized as preservatives in medicine, personal care products and cosmetics. A novel, more efficient, fast and cheap vortex-assisted liquid phase microextraction method based on deep eutectic solvents (DESs) was developed for the determination of parabens. The microextraction conditions were optimized using these solvents and the analytical parameters of the method were determined under optimal microextraction conditions. After extraction, the chromatographic separation of parabens was undertaken using high-performance liquid chromatography-UV detection. Experimental parameters, such as DES type, DES volume, dilution solvent volume and vortex extraction time were optimized. DES6 [ChCl-Ethylene glycol (1/2)] was the most suitable DES to work in this study. Detection limits for this method of 0.053 µg mL^?1 for methylparaben, 0.061 µg mL^?1 for ethylparaben, 0.049 µg mL^?1 for propylparaben and 0.052 µg mL^?1 for butylparaben were obtained. Correlation coefficients (R²) for a concentration range of 0.1–100 µg mL^?1 were higher than 0.9992 and relative standard deviation (RSD) values below 2.91% at parabens concentration of 2.5 µg mL^?1 were obtained. The results of spike/recovery values of real samples were greater than 84%. When compared with other methods, the main advantages include lower LOD, short extraction time, rapidity, repeatability and simplicity.     

A novel spectrophotometric method for determination of cyanide using cobalt (II) phthalocyanine tetracarboxylate as a chromogen

Cobalt (II) phthalocyanine tetracarboxylate [Co (II)Pc-COOH] has been prepared and used in aqueous solutions as a novel chromogenic reagent for the spectrophotometric determination of cyanide ion. The method is based on measuring the increase in the intensity of the monomer peak in the reagent absorbance at 682 nm due to the formation of a 1 : 2 [Co (II)Pc-COOH] : [CN] complex. The complex exhibits a molar absorptivity (ε) of 7.7 × 10⁴ L mol^?1 cm^?1 and a formation constant (K_f ) of 5.4 ± 0.01 × 10⁶ at 25 ± 0.1°C. Beer's law is obeyed over the concentration range 0.15–15 µg mL^?1 (5.8 × 10^?6–5.8 × 10^?4 M) of cyanide ion, the detection limit is 20 ng mL^?1 (7.7 × 10^?7 M) the relative standard deviation is ±0.7% (n = 6) and the method accuracy is 98.6 ± 0.9%. Interference by most common ions is negligible, except that by sulphite. The proposed method is used for determining cyanide concentration in gold, silver and chromium electroplating wastewater bath solutions after a prior distillation with 1 : 1 H₂SO₄ and collection of the volatile cyanide in 1 M NaOH solution containing lead carbonate as recommended by ASTM, USEPA, ISO and APAHE separation procedures. The results agree fairly well with potentiometric data obtained using the solid state cyanide ion selective electrode.     

Comparison of Boron‐Doped Diamond and Glassy Carbon Electrodes for Determination of Procaine Hydrochloride

The electrochemical oxidation of procaine hydrochloride (PC?HCL, 2‐diethylaminoethyl 4‐aminobenzoate hydrochloride) was investigated at as‐deposited boron‐doped diamond (ad‐BDD) electrode, anodically oxidized BDD (ao‐BDD) electrode and glassy carbon (GC) electrode using cyclic voltammetry (CV). Well‐defined cyclic voltammograms were obtained for PC?HCL oxidation with high signal‐to‐background (S/B) ratio, low tendency for adsorption, good reproducibility and long‐term stability at ad‐BDD electrode, demonstrating its superior electrochemical behavior and significant advantages in contrast to ao‐BDD and GC electrode. At 100 μM PC?HCL, the voltammetric S/B ratio was nearly one order of magnitude higher at an ad‐BDD electrode than that at a GC electrode. In a separate set of experiments for oxidation of 100 μM PC?HCL, 96%, 92% and 84% of the initial oxidation peak current was retained at the ad‐BDD, ao‐BDD and GC electrode, respectively, by stirring the solution after the tenth cycle. The current response was linearly proportional to the square root of the scan rate within the range 10–1000 mV s^?1 in 10 μM PC?HCL solutions, indicating that the oxidation process was diffusion‐controlled with negligible adsorption at an ad‐BDD surface. The good linearity was observed for a concentration range from 5 to 200 μM with a linear equation of y=0.03517x+0.65346 (r=0.999), and the detection limit was 0.5 μM for oxidation of PC?HCL at the ad‐BDD electrode. The ad‐BDD electrode could maintain 100% of its original activity after intermittent use for 3 months.     

Rapid Flow-Injection Method for the Determination of Colistin by Sensitized Chemiluminescence Using the Acidic Permanganate–Sulfite System

Abstract

A simple, rapid, and sensitive chemiluminescence method for the determination of colistin (Polymyxin E), a cyclic polypeptide with antibiotic effect produced by certain strains of Bacillus polymyxa, has been developed by combining a flow-injection technique and the bacteria's sensitizing effect on the chemiluminescence reaction between sulfite and acidic permanganate. The optimum conditions for chemiluminescence emission were established. The chemiluminescence was proportional to the log of concentration of colistin over the range 4–100 µg mL^?1 (3.5–87 µM). The detection limit was 1.2 µg mL^?1 (1.0 µM) of colistin. The method has been satisfactorily used for the determination of colistin in pharmaceuticals.     

Miniaturized flow-injection-analysis (μFIA) system with on-line chemiluminescence detection based on the luminol-hypochlorite reaction for the determination of ammonium in river water

A miniaturized flow-injection-analysis system constructed from glass and polydimethylsiloxane was employed for the determination of ammonium in river water. The sample was filtered and delivered to the reactor chip electro-osmotically using a disposable fritted capillary, while reagents were delivered to the system by gravity. Ammonia was mixed with the hypochlorite, to form a monochloramine. Once the alkaline luminol (3-aminophthalhydrazide) was delivered to the system, it was oxidized by the unconsumed hypochlorite emitting a bright blue light (λ _max?～?440?nm) that was detected using a miniaturized photomultiplier tube (PMT) located directly under the chip. The calibration model for ammonium standards was linear up to 0.1?µg?mL^?1 (y?=??8.96x?+?1.02; correlation coefficient, r ²?=?0.9715) over a working range of 0.0–0.5?µg?mL^?1. A detection limit of 10?±?6?µg?mL^?1 was achieved with a precision value of (RSD ≤ 6.4%), for n?=?5. A direct and standard addition method were used to determine the concentration of ammonium in a river-water sample (from the Humber Estuary, UK) which was found to be 0.075?±?0.005?µg?mL^?1, with a precision value of (RSD?≤?3.7%), for n?=?9. The results obtained showed good agreement with the average concentration 0.065?µg?mL^?1 (provided by the local environmental agency), for the analysis of ammonia at different sample points on the estuary.     

Electrochemical oxidation and determination of methylparaben at overoxidized polypyrrole film modified a boron-doped diamond electrode

Electrochemical oxidation of methylparaben (MP) is studied on an overoxidized polypyrrole (OPPy)-modified boron-doped diamond electrode using the cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques. The OPPy-modified BDD electrode displays the catalytic activity of electrooxidation of methylparaben. The modification of BDD electrode surface results in higher values of recorded oxidation currents of the methylparaben than on a bare BDD electrode. The diffusion character of recorded current is determined on the basis of the relation between the current and the scan rate. The linear relationship between methylparaben oxidation peak current is obtained in the range 1.57?×?10^??6–2.06?×?10^??5 mol L^??1. A new voltammetric procedure is proposed to quantify methylparaben in cosmetic products using an overoxidized polypyrrole (OPPy)-modified BDD electrode. The results are compared to the HPLC technique described in the literature as the reference method.