Search

A mefenamic acid sensor was prepared by the modification of a glassy carbon electrode (GCE) with graphene nano-sheets (Gr) and multi wall carbon nanotubes (MWCNT). The designed sensor (MWCNT/Gr/GCE) indicated an electrocatalytic behaviour when applied for mefenamic acid (MFA) oxidation due to good conductivity, low electron transfer resistance and catalytic effect. The suggested sensor revealed a lower overvoltage and enhanced current compared with bare GCE for the oxidation of MFA. The observations indicated that the oxidation potential of MFA is decreased more than 200 mV using the designed sensor. The percentages of MWCNTs and Gr nano materials, and pH solution were optimized. Under the optimum conditions, some kinetic parameters, such as surface coverage in a 0.5 mM [Fe(CN)6]3-/4- solution was obtained by cyclic voltammetric method. The diffusion coefficient of MFA (D) was calculated to be 2.88×10-6 cm2 s-1 by chronoamperometeric technique. The MWCNT/Gr/GCE sensor exhibited a linear dynamic range for MFA (2– 100 μM) with a detection limit of 0.66 μM by differential pulse voltammetry (DPV) technique. This sensor revealed a suitable applicability for determination of MFA in real samples (drug samples and serum solutions).

Polypyrrole modified electrode, prepared by electropolymerization of pyrrole in the presence of methyl red as a dopant, was templated with respect to Pb2+ ion and applied for potentiometric and voltammetric detection of this ion. The templating process improved the analytical response characteristics of the electrode, specially their selectivity, with respect to Pb2+ ion. The improvement depends on both the incorporated ligand (dopant) and the templating process, with the latter being more vital. The potentiometric response of the electrode was linear within the Pb2+ concentration range of 2.0×10-6 to 5.0×10-2 M with a near-Nernstian slope of 28.6 mV decade-1 and a detection limit of 7.0 ×10-7 M. The electrode was also used for preconcentration differential pulse anodic stripping voltammetry (DPASV) and results showed that peak currents for the incorporated lead species were dependent on the metal ion concentration in the range of 1.0×10-8 to 1.0×10-3 M. The detection limit of DPASV method was 3.5 ×10-9 M. The selectivity of the electrode with respect to some transition metal ions was investigated. The modified-templated electrode was used for the successful assay of lead in two standard reference material samples.

The electrocatalytic behavior of reduced nicotinamide adenine di-nucleotide (NADH) was studied at the surface of a rutin biosensor, using various electrochemical methods. According to the results, the rutin biosensor had a strongly electrocatalytic effect on the oxidation of NADH with the overpotential being decreased by about 450 mV as compared to the process at a bare glassy carbon electrode, GCE. This value is significantly greater than the value of 220 mV that was reported for rutin embedded in a lipid-cast film. The kinetic parameters of the electron transfer coefficient, a, and the heterogeneous charge transfer rate constant, kh, for the electrocatalytic oxidation of NADH at the rutin biosensor were estimated. Furthermore, the linear dynamic range; sensitivity and limit of detection for NADH were evaluated using the differential pulse voltammetry method. The advantages of this biosensor for the determination of NADH are excellent catalytic activity and reproducibility, good detection limit and high exchange current density. The rutin biosensor could separate the oxidation peak potentials of NADH and acetaminophen present in the same solution while at a bare GCE, the peak potentials were indistinguishable.

The acid–base properties of calcon (1-(2-hydroxy-1-naphthylazo)-2-naphthol-4-sulfonic acid) in water and mixed water–organic solvents at 25 °C at an ionic strength of 0.10 M are studied by a multiwavelength spectrophotometric method. The organic solvents used were the amphiprotic (methanol), dipolar aprotic (dimethylsulfoxide), and low basic aprotic (acetonitrile). To evaluate the pH absorbance data, a resolution method based on the combination of soft- and hard-modeling was applied. The acidity constants of all related equilibria were estimated using the whole spectral fitting of the collected data to an established factor analysis model. The data analysis program Datan was applied for determination of the acidity constants. The corresponding pKa values were determined in water and mixed water–organic solvents. Linear relationship between the acidity constants and the mole fraction of the different sol-vents in the mixtures exist. The effect of solvent properties on acid–base behavior is discussed.

The acid-base properties of calcon (1-(2-hydroxy-1-naphthylazo)-2- -naphthol-4-sulfonic acid) in water and mixed water-organic solvents at 25 °C at an ionic strength of 0.10 M are studied by a multiwavelength spectrophotometric method. The organic solvents used were the amphiprotic (methanol), dipolar aprotic (dimethylsulfoxide), and low basic aprotic (acetonitrile). To evaluate the pH absorbance data, a resolution method based on the combination of soft- and hard-modeling was applied. The acidity constants of all related equilibria were estimated using the whole spectral fitting of the collected data to an established factor analysis model. The data analysis program Datan was applied for determination of the acidity constants. The corresponding pKa values were determined in water and mixed water-organic solvents. Linear relationship between the acidity constants and the mole fraction of the different solvents in the mixtures exist. The effect of solvent properties on acid-base behavior is discussed.

Individual and simultaneous determinations of some phenothiazine drugs are described. The individual determination method is based on the reaction of chlorpromazine hydrochloride (CPH), promethazine hydrochloride (PH), trifluoperazine hydrochloride (TFPH), trimipramine maleate (TPM) and thioridazine hydrochloride (TRDH) with complex of [Fe(Bpy)3]3+. In the presence of phenothiazine derivatives, [Fe(Bpy)3]3+ is reduced easily to the colored complex [Fe(Bpy)3]2+, which shows an absorption maximum at 525 nm. The individual method is highly sensitive and suitable for 0.3-190 µg ml-1 concentrations, with detection limits in the range 0.18-2.46 µg ml-1. Simultaneous kinetic-spectrophotometric determination of ternary mixture of CPH, PH and TPM using principal component regression (PCR), partial least squares (PLS) and orthogonal signal correction (OSC)-PLS multivariate calibration methods is also described. The simultaneous methods are based on the difference observed in the reduction rate of the [Fe(Bpy)3]3+ complex with CPH, PH and TPM in acidic media. The results showed that the simultaneous determination of CPH, PH and TPM can be performed in the concentration ranges of 0.5-120.0, 0.3-80.0 and 5.0-100.0 µg ml-1, respectively, for three methods (PCR, PLS and OSC-PLS). The root mean square errors of prediction (RMSEP) of CPH, PH and TPM were 0.346, 0.663 and 0.820 (for PCR) 0.317, 0.659 and 0.830 (for PLS) and 0.087, 0.124 and 0.085 (for OSC-PLS), respectively. The proposed methods were successfully applied to the individual and simultaneous determination of phenothiazine derivatives in pharmaceutical preparations, the results of which compared well with those obtained by the official method, and several synthetic (spiked) samples, whereby satisfactory results were obtained.

A mefenamic acid sensor was prepared by the modification of a glassy carbon electrode (GCE) with graphene nano-sheets (Gr) and multi wall carbon nanotubes (MWCNT). The designed sensor (MWCNT/Gr/GCE) indicated an electrocatalytic behaviour when applied for mefenamic acid (MFA) oxidation due to good conductivity, low electron transfer resistance and catalytic effect. The suggested sensor revealed a lower overvoltage and enhanced current compared with bare GCE for the oxidation of MFA. The observations indicated that the oxidation potential of MFA is decreased more than 200 mV using the designed sensor. The percentages of MWCNTs and Gr nano materials, and pH solution were optimized. Under the optimum conditions, some kinetic parameters, such as surface coverage in a 0.5 mM [Fe(CN)6]3-/4- solution was obtained by cyclic voltammetric method. The diffusion coefficient of MFA (D) was calculated to be 2.88×10-6 cm² s-1 by chronoamperometeric technique. The MWCNT/Gr/GCE sensor exhibited a linear dynamic range for MFA (2-100 µM) with a detection limit of 0.66 µM by differential pulse voltammetry (DPV) technique. This sensor revealed a suitable applicability for determination of MFA in real samples (drug samples and serum solutions). [ABSTRACT FROM AUTHOR]

Individual and simultaneous determinations of some phenothiazine drugs are described. The individual determination method is based on the reaction of chlorpromazine hydrochloride (CPH), promethazine hydrochloride (PH), trifluoperazine hydrochloride (TFPH), trimipramine maleate (TPM) and thioridazine hydrochloride (TRDH) with complex of [Fe(Bpy)3]3+. In the presence of phenothiazine derivatives, [Fe(Bpy)3]3+ is reduced easily to the coloured complex [Fe(Bpy)3]2+, which shows an absorption maximum at 525 nm. The individual method is highly sensitive and suitable for 0.3–190 mg ml-1 concentrations, with detection limits in the range 0.18–2.46 mg ml-1. Simultaneous kinetic–spectrophotometric determination of ternary mixture of CPH, PH and TPM using principal component regression (PCR), partial least squares (PLS) and orthogonal signal correction (OSC)–PLS multivariate calibration methods is also described. The simultaneous methods are based on the difference observed in the reduction rate of the [Fe(Bpy)3]3+ complex with CPH, PH and TPM in acidic media. The results showed that the simultaneous determination of CPH, PH and TPM can be performed in the concentration ranges of 0.5–120.0, 0.3–80.0 and 5.0–100.0 µg ml-1, respectively, for three methods (PCR, PLS and OSC–PLS). The root mean square errors of prediction (RMSEP) of CPH, PH and TPM were 0.346, 0.663 and 0.820 (for PCR) 0.317, 0.659 and 0.830 (for PLS) and 0.087, 0.124 and 0.085 (for OSC–PLS), respectively. The proposed methods were successfully applied to the individual and simultaneous determination of phenothiazine derivatives in pharmaceutical preparations, the results of which compared well with those obtained by the official method, and several synthetic (spiked) samples, whereby satisfactory results were obtained.