Hanaa S. El-Desoky

Oxidation of Levafix CA reactive azo-dyes in industrial wastewater of textile dyeing by electro-generated Fenton's reagent

The indirect electrochemical removal of pollutants from effluents has become an attractive method in recent years. Removal (decolorization and mineralization) of Levafix Blue CA and Levafix Red CA reactive azo-dyes from aqueous media by electro-generated Fentons reagent (Fe(2+)/H(2)O(2)) using a reticulated vitreous carbon cathode and a platinum gauze anode was optimized. Progress of oxidation (decolorization and mineralization) of the investigated azo-dyes with time of electro-Fentons reaction was monitored by UV-visible absorbance measurements, Chemical oxygen demand (COD) removal and HPLC analysis. The results indicated that the electro-Fentons oxidation system is efficient for treatment of such types of reactive dyes. Oxidation of each of the investigated azo-dyes by electro-generated Fentons reagent up to complete decolorization and approximately 90-95% mineralization was achieved. Moreover, the optimized electro-Fentons oxidation was successfully applied for complete decolorization and approximately 85-90% mineralization of both azo-dyes in real industrial wastewater samples collected from textile dyeing house at El-Mahalla El-Kobra, Egypt.

Stripping voltammetric determination of silymarin in formulations and human blood utilizing bare and modified carbon paste electrodes

Silymarin is one of the most powerful natural substances that have the ability to protect and rebuild the liver cells damaged by alcohol and other toxic substances. Silymarin showed two irreversible anodic peaks in buffered solutions (pH 2.5-8.0) at either the bare carbon paste electrode or the montmorillonite-Ca modified carbon paste one. These two peaks have been attributed to oxidation of the two phenolic OH groups at positions C-20 and C-7 of silymarin molecule. A square-wave adsorptive anodic stripping voltammetry method was optimized for determination of silymarin utilizing the bare and the modified carbon paste electrodes. The method was fully validated and successfully applied for the determination of silymarin in commercial formulations and human serum without prior extraction utilizing both carbon paste electrodes. Limits of quantitation of 1 × 10(-7) and 7 × 10(-9) mol L(-1) silymarin have been achieved in bulk form or in formulations while 2 × 10(-7) and 8 × 10(-9) mol L(-1) silymarin were achieved in spiked human serum utilizing the bare carbon paste electrode and the modified one, respectively. The two electrodes exhibited excellent selectivity towards silymarin even in the presence of 10(2)to 10(3)-fold excess of its co-formulated drugs, common excipients, and common metal ions. The pharmacokinetic parameters of silymarin in plasma of healthy human volunteers were estimated following the administration of a single oral dose of 120 mg silymarin utilizing the modified carbon paste electrode. The estimated pharmacokinetic parameters were favorably compared with those reported in literature.

Stripping voltammetric methods for determination of the antiparasitic drug nitazoxanide in bulk form, pharmaceutical formulation and human serum

Cyclic voltammograms of nitazoxanide recorded at the hanging mercury drop electrode in the Britton-Robinson universal buffer of pH values 2 to 11 containing 20% (v/v) ethanol exhibited a single 4-electron irreversible cathodic peak corresponding to the reduction of its NO2 group to the hydroxylamine stage. Nitazoxanide was found to adsorb onto surface of the mercury electrode in a monolayer surface coverage of 3.16×10-10 mol cm-2 in which each adsorbed molecule occupies an area of 0.525 nm2. Based on its adsorption behavior onto the mercury electrode surface, validated linear sweep (LS), differential pulse (DP) and square wave (SW) adsorptive cathodic stripping voltammetric methods were described for determination of bulk nitazoxanide. Limits of detection of 1.5×10-10, 2.4×10-10 and 3.0×10-11 mol L-1 and limits of quantification of 5.0×10-10, 8.0×10-10 and 1.0×10-10 mol L-1 nitazoxanide in the bulk form were achieved by means of the described LS, DP and SW adsorptive cathodic stripping voltammetric methods, respectively. The described methods were successfully applied for determination of nitazoxanide in its pharmaceutical formulation (Cryptonaz powder) and in spiked human serum without the necessity for sample pretreatment, time consuming extraction steps or formation of colored chromogens prior to the analysis. Besides, nitazoxanide was successfully determined without interference from its acid or base-induced degradation products indicating the stability-indicating power of the described voltammetric methods.

Voltammetric analysis of nitroxoline in tablets and human serum using modified carbon paste electrodes incorporating mesoporous carbon or multiwalled carbon nanotubes

Mesoporous carbon (MC) was synthesized using a mesoporous SiO2 template material (SBA-15) and sucrose as the carbon source. SBA-15, MC as well as commercially obtained multi-walled carbon nanotubes (MWCNTs) were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 sorption isotherms and electrochemical impedance spectra. A carbon paste (CP) electrode modified with either MC or MWCNTs was used as a sensor for sensitive and selective determination of the nitroxoline drug. Using cyclic voltammetry, linear sweep and square-wave adsorptive stripping voltammetry, nitroxoline was found to oxidize via one developed peak at MWCNT/CP and MC/CP electrodes compared to unmodified one. This is attributed to the stronger adsorptive character, lower charge transfer resistances and higher electrocatalytic activities of modified CP electrodes than the unmodified CP electrode. A well-defined peak and high current response were observed in a B–R universal buffer (pH 2.5) following preconcentration of nitroxoline by adsorption accumulation at −0.2 V (vs. Ag/AgCl/KCls). Limits of detection of 3.0 × 10−11, 1.5 × 10−11 and 3.0 × 10−12 M nitroxoline, were obtained using the unmodified CP, MWCNT/CP and MC/CP electrodes, respectively. The utility of these sensors was examined for the determination of nitroxoline in its pharmaceutical dosage form (Nibiol® tablets) and human serum.

Stability indicating square-wave stripping voltammetric method for determination of gatifloxacin in pharmaceutical formulation and human blood

A fully validated, sensitive and precise stability-indicating square-wave adsorptive cathodic stripping voltammetric method has been developed for determination of gatifloxacin in the bulk form, pharmaceutical formulation, and in spiked human serum and real plasma samples. The achieved detection limits of gatifloxacin in the bulk form and human serum were 1.5 × 10-9 and 2.2 × 10-9 mol L-1, respectively. The described method was applied successfully for determination of gatifloxacin in formulation and human biological samples without extraction prior to the analysis. No significant interferences from common excipients, some common metal ions, organic species, co-administrated drugs and from the acid-induced degradation products were obtained during analysis of gatifloxacin in the various analyzed samples. Besides, pharmacokinetic parameters of gatifloxacin in plasma of healthy volunteers following the administration of an oral single dose (400 mg gatifloxacin) were also estimated by means of the described stripping voltammetric method.

Electrochemical determination of muscle relaxant drug tetrazepam in bulk form, pharmaceutical formulation, and human serum

Tetrazepam dissolved in the Britton-Robinson universal buffer of various pH values (2.5–11.5) containing 10 vol. % of ethanol was reduced at the mercury electrode in a single 2-electron irreversible step due to reduction of the 4,5 C=N double bond of the seven-membered ring. Differential pulse polarography (DPP) and adsorptive cathodic stripping voltammetry (AdCSV) techniques (Linear sweep LS, differential pulse DP and square-wave SW modes) for quantification of tetrazepam in bulk form and in myolastan tablets are presented. Moreover, the described linear sweep, differential pulse, and square-wave adsorptive cathodic stripping voltammetry was successfully applied in quantification of tetrazepam in spiked human serum without any prior extraction of the drug. The obtained results showed an increased sensitivity of the described electro-analytical procedures for the quantification of tetrazepam in the following order DPP, DP-AdCSV, LS-AdCSV, and SW-AdCSV, since the observed limits of tetrazepam quantitation by these electroanalytical techniques were 5 × 10−6 mol L−1, 3 × 10−7 mol L−1, 1 × 10−8 mol L−1, and 3 × 10−9 mol L−1, respectively.

Electrochemistry of the antibacterial and antifungal drug nitroxoline and its determination in bulk form, pharmaceutical formulation and human blood

Nitroxoline has been reduced at the mercury electrode in buffered solutions (pH 2-11) in two irreversible cathodic steps. The first step was attributed to reduction of -NO(2) group to the hydroxylamine stage and the second one to reduction-saturation of the C=N double bond. DC-polarographic and various adsorptive stripping voltammetric methods were developed for determination of nitroxoline in bulk form. Limits of quantitation of 1.02×10(-6), 3.05×10(-8), 9.01×10(-9), and 9.12×10(-10)M nitroxoline were achieved by means of the developed DC-polarography, differential-pulse-, linear-sweep-, and square-wave-adsorptive cathodic stripping voltammetric methods, respectively. All these electroanalytical methods were successfully applied for determination of nitroxoline in its Nibiol(®) tablets. While only the developed adsorptive stripping voltammetry methods were successfully applied for determination of the drug in spiked human serum and for pharmacokinetic studies in real human plasma. The analysis was carried out without interference from common excipients and without the necessity for prior extraction or interaction with any reagent during the analysis.

Trace determination of vardenafil hydrochloride in commercial formulation and human serum by adsorptive anodic stripping voltammetry at a carbon paste electrode

The electrochemical behavior of vardenafil HCl (VRL) at a carbon paste electrode (CPE) was investigated by cyclic voltammetry, and the mechanism of its oxidation was suggested and discussed. A simple Nujol-based CPE in combination with a sensitive square-wave adsorption anodic stripping voltammetry method was described for trace determination of VRL. The described method showed excellent performance for trace determination of VRL in its formulation “Levitra® tablets” without interference from excipients. The results were statistically compared with those obtained with an established HPLC method; nonsignificant differences were found between the described voltammetric and HPLC methods. The described stripping voltammetric method is highly sensitive (limit of detection = 3 × 10−10 mol L−1 and limit of quantitation = 1 × 10−9 mol L−1). It was successfully applied for the determination of VRL in spiked human serum without the necessity for pretreatment and/or time-consuming extraction steps prior to the analysis.

Adsorptive stripping voltammetry determination of the hormone therapy Raloxifene HCl in formulation and human serum

Raloxifene HCl (RLX) was found to strongly adsorb onto surface of the mercury electrode in a monolayer surface coverage of 5.724 × 10-10 mol cm-2. Two precise, rapid and extraction-free linear sweep and square wave adsorptive cathodic stripping voltammetry (LS-AdCSV and SW-AdCSV, respectively) methods are described for trace quantitation of RLX in bulk form, commercial formulation and human serum. Limits of quantification (LOQ) of 2.0 × 10-9 and 5.0 × 10-11 mol L-1 RLX in bulk form and 4.0 × 10-9 and 1.0 × 10-10 mol L-1 RLX in spiked human serum were achieved by the described LS-AdCSV and SW-AdCSV methods, respectively. Insignificant interferences from some common excipients, metal ions and co-administrated drugs were obtained. LOQ achieved by the methods are low as well as they offer good possibilities for determination of drug in low-dosage pharmaceutical preparations. However, the SW-AdCSV method described is sensitive enough to assay the drug also in human serum.

Electrochemical reduction and stripping voltammetric determination of the anti-glaucoma drug levobunolol HCl in formulation and human serum at the mercury electrode

Levobunolol HCl is a potent non-selective s-adrenoceptor blocking agent used for the topical treatment of increased intraocular pressure in patients with chronic open angle glaucoma or ocular hypertension. Precise, rapid and extraction-free square-wave adsorptive cathodic stripping voltammetry (SW-AdCSV) method has been described for trace quantitation of levobunolol HCl in bulk form, commercial formulation (ophthalmologic drops) and human serum. Limits of quantification (LOQ) of 1.0 × 10-10 mol L-1 (in bulk form) and 2.5 × 10-10 mol L-1 levobunolol HCl (in spiked human serum) were achieved by the described method. Insignificant interferences from excipients associated with formulation of levobunolol HCl and from some common metal ions, co-administrated drugs, some other s-blocker agents and its metabolite dihydrolevobunolol that are likely to be present in the biological fluids were obtained. The described SW-AdCSV method is sensitive enough to assay the drug in human serum compared to most of the reported methods.