A new diclofenac membrane sensor based on its ion associate with crystal violet. Application to diclofenac determination in urine and pharmaceuticals

A novel diclofenac ion-selective electrode has been prepared and used in pharmaceutical analysis. The ion-associate of diclofenac with basic dye (crystal violet) was used as the membrane carrier. Among the four different solvent mediators tested, dibutylphthalate (DBP) exhibited proper behavior including the Nernstian slope of the calibration curve, fast response time and good reproducibility of the emf values. The electrode exhibits a Nernstian slope of 59 ± 1 mV decade^?1 for diclofenac in the concentration range 5.0 × 10^?5-5.0 × 10^?2 M with the limit of detection of 2.5 × 10^?5 M. The electrode displays good sensitivity with the respect to a number of common inorganic and organic species. It can be used in a pH range of 6–11. The membrane sensor was successfully applied to the determination of diclofenac in capsules and for its recovery from urine samples.     

An ionic liquid-based sensor for diclofenac determination in water

This paper details a miniaturised, solid state ion-selective electrode selective for diclofenac. The sensor comprises a novel ionic liquid electroactive material – an imidazolium–diclofenac ion associate. The ion associate is present in a plasticised poly(vinyl chloride) (PVC) membrane on planar carbon electrodes, with an intermediate poly(3,4-ethylenedioxythiophene) layer. The sensitivity and selectivity of the sensor were determined using chronopotentiometric methods. In response to diclofenac, a slope of ?53.3 ± 3.6 mV/dec was observed. A limit of detection of 2.90 × 10^?3 g L^?1 is reported, with a linear range of 3.18 × 10^?3 g L^?1 to 3.18 g L^?1. The sensors show good selectivity towards diclofenac against pertinent interferent molecules, with a response time of <15 s.     

Design of a Vitamin B1‐Selective Electrode Based on an Ion‐Pair and Its Application to Pharmaceutical Analysis

Vitamin B₁‐selective electrodes with PVC membrane were developed that contain ion associates of vitamin B₁ with an inorganic anion, BiI₄^?, and an organic anion, brilliant yellow, as electrode‐active substances. The linearity ranges of the electrode function are 1.0×10^?5–1.0×10^?2 and 1.0×10^?4–1.0×10^?2 M, the electrode function slopes are 33.0±1.0 and 33.1±1.1 mV decade^?1, the detection limits are 5.5×10^?6 and 8.3×10^?5 M for BiI₄^? and brilliant yellow respectively. The working range of pH is 5–12. The efficiency of the use of electrodes for the vitamin B₁ content control in multivitamin pharmaceutical preparations was shown by direct potentiometry and potentiometric titration methods.     

Acetylferrocene Modified Carbon Paste Electrode; A Sensor for Electrocatalytic Determination of Hydrazine

The electrocatalytic oxidation of hydrazine at a carbon paste electrode spiked with acetylferrocene as a mediator was studied by cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. In contrast to other ferrocenic compounds, acetylferrocene exhibits a chemical irreversible behavior, but it can act as an effective mediator for electrocatalytic oxidation of hydrazine, too. The heterogeneous electron transfer rate constant between acetylferrocene and the electrode substrate (carbon paste) and the diffusion coefficient of spiked acetylferrocene in silicon oil were estimated to be about 3.45×10^?4 cm s^?1 and 4.45×10^?9 cm² s^?1, respectively. It has been found that under the optimum conditions (pH 7.5) the oxidation of hydrazine occurs at a potential of about 228 mV less positive than that of an unmodified carbon paste electrode. The catalytic oxidation peak current of hydrazine was linearly dependent on its concentration and the obtained linear range was 3.09×10^?5 M–1.03×10^?3 M. The detection limit (2σ) has been determined as 2.7×10^?5 M by cyclic voltammetry. Also, the peak current was increased linearly with the concentration of hydrazine in the range of 1×10^?5 M–1×10^?3 M by differential pulse voltammetry with a detection limit of 1×10^?5 M. This catalytic oxidation of hydrazine has been applied as a selective, simple, and precise new method for the determination of hydrazine in water samples.     

Novel Gadolinium PVC‐Based Membrane Sensor Based on Omeprazole as an Antibiotic

A novel gadolinium ion‐selective electrode based on the antibiotic omeprazole as membrane carrier was prepared. The electrode has a linear dynamic range between 1.0×10^?1 and 1.0×10^?5 M, with a Nernstian slope of 19.3 ± 0.3 mV decade^?1 and a detection limit of 5.0×10^?6 M. The potentiometric response is independent of the pH of the solution in the pH range 4.0–10.0. The electrode possesses the advantages of short conditioning time, fast response time and especially, very good selectivity over a large number of other cations. The electrode can be used for at least 2 months without any considerable divergence in potentials. It was used as an indicator electrode in potentiometric titration of Gd(III) ions with EDTA.     

Ionic liquids with an anion of N-lauroyl sarcosinate in membranes of ion-selective electrode

The study considers solubility in water, extractivity, and electrode properties of ionic liquids (IL), lauroyl tetrahexylammonium (THALS) and tetraoctylammonium lauroyl sarcosinate (TOALS). The values of solubility, found by potentiometry using ion-selective membranes of PVC-electrodes (ISE) have appeared to be 3.0 ± 0.4 mM and 0.011 ± 0.005 mM, for THALS and TOALS, respectively. Both IL quantitatively recover nitrophenol (99.9%) into chloroform from aqueous solutions in the pH range from 2 to 12. The application of IL as the active components of PVC-ISE enables the determination of lauroyl sarcosinate anion in the concentration range 1 × 10^?2?C1 × 10^?4 M for THALS and 1 × 10^?2?C1 × 10^?5 M for TOALS and the determination of mononitrophenols, 2,4-dinitrophenols and picrates (1 × 10^?2 M?C1 × 10^?5 M). A solid-state sensor based on screen-printed electrode modified by TOALS IL has been proposed. The electrode has been used for the determination of 4-nitrophenol in the concentration range 1 × 10^?2?C1 × 10^?5 M, the operational stability of the electrode is 10 days.     

Potentiometric sensors based on organic ion exchangers for determining tetraalkylammonium salts

Potentiometric sensors with plasticized polymer membranes based on organic ion exchangers, tetraalkylammonium dodecyl sulfates (benzyldimethyldodecylammonium, benzyldimethyltetradecylammonium, dimethyldistearylammonium), have been proposed for the determination of quaternary ammonium salts in model solutions and KATAPAV technical solutions. The thermal stability, composition, and solubility product have been estimated. It has been shown that ion associates are stable to 60?C70°C, K _S varies in the range from 2 × 10^?8 to 5 × 10^?10. The basic electrochemical parameters of the sensors have been determined as well, such as linearity ranges of the electrode function (5 × 10^?5 (5 × 10^?6)?1 × 10^?2 (1 × 10^?3) M) and slopes of the electrode functions (47?C59 mV/pc), response time (60?C90 sec), potential drift (2?C3 mV/day), operation period (3?C4 months), limits of detection for tetramethylammonium salts (1 × 10^?5?4 × 10^?7 M).     

Novel PVC-based coated graphite electrode for selective determination of quinoline yellow

Novel coated graphite electrode (CGE) for the determination of quinoline yellow (QY), an artificial food colorant, was evaluated based on the use of tetraphenylphosponium-QY ion-pair complex as the electroactive substance. The electrode revealed linear emf-pQY response over wide concentration ranges (1.0 × 10^?1 ～ 5.0 × 10^?5 M) with a slope ?30.1 ± 0.2 mV decade^?1 and a limit of detection of 4.0 × 10^?5 M. The electrode showed good stability, reproducibility and fast response (<5 s). It can be used in wide pH range (4.7–10.7) and was successfully applied to determination of quinoline yellow in artificial mixtures and commercial soft drinks. The results obtained with the electrode were in good agreement with the value obtained by using HPLC measurements, as an official method.     

Electrochemical reduction behaviour of the synthetic pyrethroid insecticide cyfluthrin and its determination in formulations and environmental samples

The polarographic behaviour of cyfluthrin (CY), an α-cynoester pyrethroid, was studied using a dropping mercury electrode and hanging mercury drop electrode in methanolic Britton–Robinson (B–R) buffer of pH 2.0–12.0 with different ionic media. The nature of the electrode process was examined, the number of electrons was evaluated, and the reduction mechanism was proposed. Quantitative determination was achieved in the concentration range of 6.0?×?10^?8 to 1.15?×?10^?5?mol?dm^?3 using a differential pulse polarographic method with a lower detection limit of 2.4?×?10^?8?mol?dm^?3. The proposed method was successfully applied in the determination of CY in formulations, grains, soils, and spiked water samples.     

Electrochemical determination of tryptophan based on silicon dioxide nanopartilces modified carbon paste electrode

Silicon dioxide nanoparticles modified carbon paste electrode was fabricated and used for electrochemical investigation of tryptophan. Compared with the unmodified electrode, the peak current significantly increased. Experimental conditions for tryptophan determination were optimized. Linear relationship between the peak current and tryptophan concentration was obtained in the range of 1.0 × 10^?7?5.0 × 10^?6 mol L^?1 and 5.0 × 10^?6?5.0 × 10^?5 mol L^?1 with an estimated detection limit of 3.6 × 10^?8 mol L^?1 (S/N = 3). Tryptophan in pharmaceutical and human serum samples were successfully determined by the proposed method.     

Determination of pesticides in vegetable samples using an acetylcholinesterase biosensor based on nanoparticles ZrO2/chitosan composite film

An amperometric pesticides inhibition biosensor has been developed and used for determination of pesticides in vegetable samples. To eliminate the interference of ascorbic acid, multilayer films of polyelectrolyte (chitosan/polystyrensulfonate) were coated on the glass carbon electrode. Then, acetylcholinesterase was immobilized on the electrode based on surface-treated nanoporous ZrO₂/chitosan composite film as immobilization matrix. As a modified substrate, acetylthiocholine was hydrolysed by acetylcholinesterase and produced thiocholine which can be oxidized at +700?mV vs. SCE. Pesticides inhibit the activity of enzyme with an effect of decreasing of oxidation current. The experimental conditions were optimized. The electrode has a linear response to acetylthiocholine within 9.90?×?10^?6 to 2.03?×?10^?3?M. The electrode provided a linear response over a concentration range of 6.6?×?10^?6 to 4.4?×?10^?4?M for phoxim with a detection limit of 1.3?×?10^?6?M, over a range of 1.0?×?10^?8 to 5.9?×?10^?7?M for malathion, and over a range of 8.6?×?10^?6 to 5.2?×?10^?4?M for dimethoate. This biosensor has been used to determine pesticides in a real vegetable sample.     

Simultaneous determination of dopamine and serotonin by use of covalent modification of 5-hydroxytryptophan on glassy carbon electrode

An electrochemical biosensor was fabricated by covalent modification of 5-hydroxytryptophan (5-HTP) on the surface of glassy carbon electrode (GCE). The electrode, denoted as 5-HTP/GCE, was characterized by X-ray photoelectron spectroscopy, cyclic voltammetry and differential pulse voltammetry. For comparison, tryptophan modified GCE (TRP/GCE) and serotonin modified GCE (5-HT/GCE) were prepared by the same method. It was found that electrocatalytic ability of these electrodes was in the order of 5-HTP/GCE?>?TRP/GCE?>?5-HT/GCE for the oxidation of dopamine (DA) and 5-HT. The sensor was effective to simultaneously determine DA and 5-HT in a mixture. It can resolve the overlapping anodic peaks into two well-defined voltammetric peaks at 0.24 and 0.39 V (versus SCE). The linear response is in the range of 5.0?×?10^?7–3.5?×?10^?5 mol L^?1 with a detection limit of 3.1?×?10^?7 mol L^?1 for DA, and in the range of 5.0?×?10^?6–3.5?×?10^?5 mol L^?1 with a detection limit of 1.7?×?10^?6 mol L^?1 for 5-HT (s/n?=?3), respectively.     

Gold-nanoparticle on the surface of L-cysteine modified gold electrode and its application

A sensor based on gold nanoparticle on the surface of L-cysteine modified gold electrode is prepared. Electrochemical behavior of dopamine hydrochloride is investigated. The linear relation between peak current of dopamine hydrochloride and scan speed in the range of 10 to 1000 mV s^?1 indicates that a diffusion-adsorption controls the process. The linearity range is 1.05 × 10^?5–7.38 × 10^?4 M with detection limit of 1.05 × 10^?6 M. The recoveries were in the range from 99.8 to 101.5% with relative standard deviations of 1.3 ～ 2.3% (n = 6). The modified electrode under ambient conditions over a period of 2 weeks has an excellent repeatability and reproducibility.     

Electrocatalytic oxidation and the mechanism of dopamine on a MWNT-modified glassy carbon electrode

The electrochemical behavior of dopamine (DA) at a MWNTs-modified glassy carbon electrode was investigated by cyclic voltammetry (CV), square wave voltammetry (SWV). The MWNTs modified electrode exhibited marked promotion of the electrochemical reaction of DA in different environments. Under optimum conditions, the peak currents of SWV of DA were increased linearly with incremental concentration of DA in the range from 5 × 10^?7 to 1 × 10^?5 mol L^?1. The limit of detection is 3 × 10^?7 mol L^?1.     

Determination of ferulic acid in Chinese proprietary medicine based on a poly-glutamic acid film sensor

The poly-glutamic acid modified electrode has been prepared by direct electro-polymerization of D-glutamic acid on the surface of glassy carbon electrode. In pH 4.2, 0.1 mol L^?1 HAc-NaAc buffer solution, the film modified electrode exhibited remarkable enhancement effect to the electrochemical responses of ferulic acid. The action mechanism was preliminarily explored. In the range of 2.0 × 10^?7 to 1.0 × 10^?5 mol L^?1, and 1.0 × 10^?5 to 3.0 × 10^?4 mol L^?1, the oxidation peak current has a linear relationship to the concentration, and the detection limit was estimated to be 7.0 × 10^?8 mol L^?1. This method has been adopted to detect trace amount of ferulic acid in Chinese proprietary medicine, and the recovery was from 97.8 to 102.4%.     

Simultaneous Determination of Pb and Cd Traces in Water Samples by Anodic Stripping Voltammetry Using a Modified GC Electrode

The determination of Pb and Cd with a Nafion‐modified glassy carbon electrode and Cu‐DPABA complex (Cu‐DPABA–NA/GCE; DPABA is methyl 3,5‐bis{bis‐[(pyridin‐2‐yl)methyl]amino}methyl‐benzoate) as an alternative electrode for anodic stripping voltammetry was described. Pb and Cd were accumulated in acetate buffer pH 4 at a potential of ?1.4 V (vs. Ag/AgCl electrode) for 120 s followed by a DPASV scan from ?1.2 to ?0.2 V. Under optimum conditions the calibration curves were linear in the range of 4.8×10^?9–5.0×10^?5 and 5.0×10^?9–5×10^?5 mol L^?1 for Pb and Cd, respectively. Detection limits were 1.8×10^?9 and 1.2×10^?9 mol L^?1 for Pb and Cd, respectively. Different parameters and conditions, such as membrane ingredients, accumulation time, potential and pH value were optimized. A study of interfering substances was also performed. A significant increase in current was achieved at the modified electrode in comparison with the bare glassy carbon electrode. The validation of the proposed method was made by Pb and Cd determination in the certified reference material Groundwater CRM 610 (BCR, Community Bureau of Reference, Brussels, Belgium). The electrode was successfully applied for determination of Pb and Cd in river water with a high content of organic contaminants without any pretreatment.     

One-step construction of an electrode modified with electrodeposited Au/SiO2 nanoparticles, and its application to the determination of NADH and ethanol

A new electrode was developed by one-step potentiostatic electrodeposition (at ?2.0 V for 20 s) of Au/SiO₂ nanoparticles on a glassy carbon electrode. The resulting electrode (nano-Au/SiO₂/GCE) was characterized by scanning electronic microscopy, X-ray photoelectron spectroscopy and electrochemical techniques. The electrochemical behavior of dihydronicotinamide adenine dinucleotide (NADH) at the nano-Au/SiO₂/GCE were thoroughly investigated. Compared to the unmodified electrode, the overpotential decreased by about 300 mV, and the current response significantly increased. These changes indicated that the modified electrode showed excellent catalytic activity in the oxidation of NADH. A linear relationship was obtained in the NADH concentration range from 1.0?×?10^?6 to 1.0?×?10^?4 mol?L^?1. In addition, amperometric sensing of ethanol at the nano-Au/SiO₂/GCE in combination with alcohol dehydrogenase and nicotinamide adenine dinucleotide was successfully demonstrated. A wide linear response was also found for ethanol in the range from 5.0?×?10^?5 to 1.0?×?10^?3 mol?L^?1 and 1.0?×?10^?3 to 1.0?×?10^?2 mol?L^?1, respectively. The method was successfully applied to determine ethanol in beer and biological samples.     

Preparation of Cu (II) imprinted polymer electrode and its application for potentiometric and voltammetric determination of Cu (II)

The Cu (II) imprinted polymer glassy carbon electrode (GCE/Cu-IP) was prepared by electropolymerization of pyrrole at GCE in the presence of methyl red as a dopant and then imprinting by Cu²⁺ ions. This electrode was applied for potentiometric and voltammetric detection of Cu²⁺ ion. The potentiometric response of the electrode was linear within the Cu²⁺ concentration range of 3.9 × 10^?6 to 5.0 × 10^?2 M with a near-Nernstian slope of 29.0 mV decade^?1 and a detection limit of 5.0 × 10^?7 M. The electrode was also used for preconcentration anodic stripping voltammetry and results exhibited that peak currents for the incorporated copper species were dependent on the metal ion concentration in the range of 1.0 × 10^?8 to 1.0 × 10^?3 M and detection limit was 6.5 × 10^?9 M. Also the selectivity of the prepared electrode was investigated. The imprinted polymer electrode was used for the successful assay of copper in two standard reference material samples.     

Self-assembly of ultra-small gold nanoparticles on an indium tin oxide electrode for the enzyme-free detection of hydrogen peroxide

A novel enzyme-free electrochemical sensor for H₂O₂ was fabricated by modifying an indium tin oxide (ITO) support with (3-aminopropyl) trimethoxysilane to yield an interface for the assembly of colloidal gold. Gold nanoparticles (AuNPs) were then immobilized on the substrate via self-assembly. Atomic force microscopy showed the presence of a monolayer of well-dispersed AuNPs with an average size of ~4 nm. The electrochemical behavior of the resultant AuNP/ITO-modified electrode and its response to hydrogen peroxide were studied by cyclic voltammetry. This non-enzymatic and mediator-free electrode exhibits a linear response in the range from 3.0?×?10^?5 M to 1.0?×?10^?3 M (M?=?mol?·?L^?1) with a correlation coefficient of 0.999. The limit of detection is as low as 10 nM (for S/N?=?3). The sensor is stable, gives well reproducible results, and is deemed to represent a promising tool for electrochemical sensing.

Zinc-Selective Membrane Electrode Based On 5, 6, 14, 15-Dibenzo-l, 4-Dioxa-8, 12-Diazacyclopentadecane-5, 14-Diene

ABSTRACT

A new PVC membrane for zinc ions based on DBDA15C4 as membrane carrier was prepared. The electrode shows a linear stable response over a wide concentration range (5.0 × 10^?5-1.0 × 10^?1 M) with a slope of 22 mV/decade and a limit of detection of 3.0 × 10^?5 M (2.0 μg/ml). It has a very short response time of less than 5 s and can be use for at least 11 months without any divergence in potential. The zinc ion-selective electrode exhibited very good selectivities with respect to alkali, alkaline earth and some transition and heavy metal ions and could be used in a pH range 1.5-7.0. It was successfully applied for the direct determination of zinc in a pharmaceutical sample and, as an indicator electrode, in potentiometric titration of Zn²⁺ ions.