Adsorptive behavior and electrochemical determination of the anti-fungal agent ketoconazole

The adsorptive properties and electrochemical behavior of ketoconazole, an oral anti-fungal agent, are demonstrated at a glassy carbon electrode. The adsorption of the compound obeys the Frumkin isotherm with an interaction factor (α) of 0.985 and adsorptive coefficient (β) of 1.98 × 10⁶ L mol^–1. The Gibbs energy of adsorption (ΔG) is –3.59 × 10⁴ J mol^–1 at 25?°C. A very sensitive electroanalytical method has been developed for determination of the drug with a detection limit of 4.0 × 10^–11 mol L^–1. Relationships between stripping current and concentration of ketoconazole were linear in the range 10^–6–10^–10 mol L^–1 with different preconcentration periods. The method has been used to measure the ketoconazole content of tablets.     

Electrochemical behavior of valsartan and its determination in capsules

Electrochemical behavior of valsartan has been carried out in Britton-Robinson (B-R) buffer solution at pH 7.0 at the mercury film electrode (MFE) by cyclic, linear sweep, differential-pulse and square-wave voltammetry. The property of valsartan adsorption at the MFE using accumulation potential of +0.10 V was observed. The effects of experimental parameters on electrochemical process at the MFE were discussed. Differential-pulse adsorptive stripping and square-wave adsorptive stripping voltammetry for the valsartan determination were proposed, linearity was found in the range of 6.0 x 10(-8) to 4.0 x 10(-6)mol/L. The detection limits were 2.93 x 10(-9) and 3.27 x 10(-9)mol/L, respectively. The proposed methods were also applied to the commercial valsartan with good recoveries.     

Electrochemical behavior and detection of plant hormone 6-benzyl adenine in acetate buffer at mercury electrode.

The electrochemical behavior of 6-benzyl adenine (6-BA) has been studied in 0.1 mol L(-1) HAc-NaAc solution (pH 3.8). Cyclic voltammetry, single-sweep polarography and direct current polarography were employed to clarify the mechanism of the electrode process; the kinetic parameters of the rate-determining step were determined. Reduction of 6-BA involves two pH-dependent processes, corresponding to the overall irreversible reduction of the 1,6 and 3,2 N=C bonds. Each reduction stage consists a preprotonation of the nitrogen atom at the electroactive site and a rapid two-electron transfer. In the presence of 6-BA, the reduction potentials of some ions were shifted. Under the given conditions, 6-BA displays one irreversible reduction peak controlled by adsorption. Two linear response were observed in the range 2.0 x 10(-8) - 8.0 x 10(-7) mol L(-1) and the range 1.0 x 10(-6) - 8.0 x 10(-6) mol L(-1), with correlation coefficients of 0.9995 and 0.9998, respectively. The detection limit is 7.1 x 10(-9) mol L(-1). The method had been applied to the determination of 6-BA in bean sprout samples with satisfactory results.     

Amperometric determination of glutathione and cysteine on a Pd-IrO(2) modified electrode with high performance liquid chromatography in rat brain microdialysate

A Pd/IrO(2) co-electrodeposited glassy carbon electrode was prepared and the electrochemical behavior of glutathione (GSH) at this chemically modified electrode (CME) has been studied by cyclic voltammetry (CV). The results indicated that the modified electrode efficiently exhibited electrocatalytic oxidation for GSH with relatively high sensitivity, stability, and long-life. Coupled with high-performance liquid chromatography (HPLC), the Pd/IrO(2) modified electrode was utilized for the electrochemical detection (ECD) of the thiocompounds, glutathione and cysteine (Cys). The peak currents were linear with the substance concentrations in the range of 1.0 x 10(-5) mol L(-1) to 8.0 x 10(-4) mol L(-1) for GSH and 4.0 x 10(-6) mol L(-1) to 2.0 x 10(-4) mol L(-1) for Cys. The detection limits were 2.0 x 10(-6) mol L(-1) for GSH and 5.0 x 10(-7) mol L(-1) for Cys with S/N of 3. The method has been successfully applied to assess the contents of GSH and Cys in rat brain microdialysates.     

Carbon paste electrode based on surface activation for trace adriamycin determination by a preconcentration and voltammetric method.

A voltammetric determination of adriamycin (ADM) at a carbon paste electrode (CPE) in the presence of cetyltrimethylammonium bromide (CTAB) is described. ADM strongly adsorbs on the surface of the electrode by the adsorption of CTAB, thereby affecting the reduction current. This method provides a detection limit below 10(-10) mol/L for ADM. The experimental parameters, which influence the voltammetric responses of ADM, e.g. the pH value, variety and concentration of surfactants and the scan rate, were optimized. The reduction peak current changes linearly with the ADM concentration over the range from 2.5 x 10(-8) mol/L to 5 x 10(-6) mol/L. The detection limit is 4 x 10(-10) mol/L for an accumulation time of 3 min. The coefficient of variation, determined at 4 x 10(-6) mol/L ADM, is 3.0% (n = 8). Using this method, ADM in the patient's urine samples, which undergoes active ADM chemotherapy, was determined.     

Phase-selective a.c. adsorptive stripping voltammetry of lumazine on a hanging mercury drop electrode

The electrochemical behavior of lumazine (LMZ), an important antibacterial agent, has been studied at the hanging mercury drop electrode (HMDE). The nature of the process taking place at the HMDE was clarified. Its adsorption behavior at HMDE has been studied by using a.c and cyclic voltammetry (CV). Both the molecule and its reduced product appeared to be adsorbed at the surface of the electrode. Controlled adsorptive accumulation of LMZ on the HMDE provides the basis for the direct stripping measurement of that compound in the subnanomolar concentration level. Experimental and instrumental parameters for the quantitative determination were optimized. Phase-selective a.c voltammetry provided the best signal and gave a detection limit of 0.15 microg L(-1) (9.0 x 10(-10) mol/L) LMZ in aqueous solution. Molecules or ions which may interfere were studied.     

Simultaneous square-wave voltammetric determination of aspartame and cyclamate using a boron-doped diamond electrode

A simple and highly selective electrochemical method was developed for the simultaneous determination of aspartame and cyclamate in dietary products at a boron-doped diamond (BDD) electrode. In square-wave voltammetric (SWV) measurements, the BDD electrode was able to separate the oxidation peak potentials of aspartame and cyclamate present in binary mixtures by about 400 mV. The detection limit for aspartame in the presence of 3.0x10(-4) mol L(-1) cyclamate was 4.7x10(-7) mol L(-1), and the detection limit for cyclamate in the presence of 1.0x10(-4) mol L(-1) aspartame was 4.2x10(-6) mol L(-1). When simultaneously changing the concentration of both aspartame and cyclamate in a 0.5 mol L(-1) sulfuric acid solution, the corresponding detection limits were 3.5x10(-7) and 4.5x10(-6) mol L(-1), respectively. The relative standard deviation (R.S.D.) obtained was 1.3% for the 1.0x10(-4) mol L(-1) aspartame solution (n=5) and 1.1% for the 3.0x10(-3) mol L(-1) cyclamate solution. The proposed method was successfully applied in the determination of aspartame in several dietary products with results similar to those obtained using an HPLC method at 95% confidence level.     

桑色素极谱行为的研究

研究了桑色素在pH=1～14的水溶液中的极谱行为. 于不同pH范翻内得列了四个还原波. 研究证实在pH<4条件下获得的P_1波为表面催化氢波. 其余三个波为不同形态桑色素的单电子吸附还原波, 并伴有随后化学反应过程. 测得在单分子层饱和吸附条件下, 每一个桑色素分子所占汞电极面积为1.36 nm.     

核固红及稀土核固红极谱行为的研究

在由酸性至碱性的水溶液中均获得了核固红的极谱吸附波, 证实在酸性底液中核固红在汞电极上的吸附符合Frumkin等温式. 对pH由7至11的碱性底液中核固红电还原的ECE机制作了研究, 还获得并研究了在pH11附近, 乙二胺-氯化钾底液中的稀土-核固红体系的极谱络合吸附波。     

Determination of the antiretroviral drug nevirapine in diluted alkaline electrolyte by adsorptive stripping voltammetry at the mercury film electrode

This paper describes a stripping method for the determination of nevirapine at the submicromolar concentration levels. The method is based on controlled adsorptive accumulation of nevirapine at thin-film mercury electrode, followed by a linear cyclic scan voltammetry measurement of the surface species. Optimal experimental conditions include a 2.0 x 10(-3) mol L(-1) NaOH solution (supporting electrolyte), an accumulation potential of -0.20 V, and a scan rate of 100 mV s(-1). The response of nevirapine is linear over the concentration range 0.01-0.14 ppm. For an accumulation time of 6 minutes, the detection limit was found to be 0.87 ppb (3.0 x 10(-9) mol L(-1)). More convenient methods to measure the nevirapine in presence of the efavirenz, acyclovir, didanosine, indinavir, nelfinavir, saquinavir, lamivudine, zidovudine and metals ions were also investigated. The utility of this method is demonstrated by the presence of nevirapine together with ATP or DNA.     

Determination of the herbicide desmetryne in organised media by adsorptive stripping voltammetry

An electroanalytical method for the determination of the herbicide desmetryne at nanomolar levels in dispersed media, based on adsorptive stripping voltammetry, is reported. The adsorption of desmetryne at the hanging mercury drop electrode was checked both in micellar solutions, where the anionic surfactant sodium pentanesulphonate was chosen as the most suitable surfactant agent, and in oil-in-water emulsions prepared with ethyl acetate as the organic solvent. In a micellar medium formed with 0.02% sodium pentanesulphonate and with 0.1 mol l(-1) Britton-Robinson buffer (pH 1.5), the herbicide could be determined over the 1.0 x 10(-8)-4.0 x 10(-7) mol l(-1) concentration range, when an accumulation potential of -0.70 V was applied for 50 s. On the other hand, in an oil-in-water emulsion formed with 2% ethyl acetate and 0.04% sodium pentanesulphonate as emulsifying agent in 0.1 mol l(-1) HClO(4), desmetryne could be determined over the 2.0 x 10(-9)-1.0 x 10(-7) mol l(-1) concentration range. The limits of detection were 2.4 x 10(-9) and 4.2 x 10(-10) mol l(-1) in micellar and emulsified media, respectively, with R.S.D.s (n=10) 3.6 and 3.7%. The degree of interference from some other s-triazines on the desmetryne differential pulse response was also evaluated. Finally, the method developed in emulsified medium was applied to the determination of desmetryne in spiked apple juice.     

Anodic stripping voltammetric determination of mercury by use of a sodium montmorillonite-modified carbon-paste electrode

A sodium montmorillonite (SWy-2)-modified carbon-paste electrode has been examined for determination of trace levels of mercury. Because of its strong cation-exchange and adsorptive characteristics, SWy-2 greatly improves the sensitivity of determination of Hg(2+). Hg(2+) is preconcentrated and reduced on the modified electrode surface at -0.40 V and then stripped from the electrode surface during the positive potential sweep. The conditions used for determination, e.g. supporting electrolyte, pH, amount of SWy-2, accumulation potential, and accumulation time, were optimized. The peak current was linearly dependent on the concentration of mercury from 1 x 10(-9) to 5 x 10(-7) mol L(-1). The detection limit (signal-to-noise ratio=3) was 1 x 10(-10) mol L(-1) after accumulation for 6 min. When the SWy-2-modified carbon-paste electrode was used to detect mercury in water samples the average recovery was 101.11%.     

Differential-pulse polarography (DPP) determination of betamethasone valerate in dosage form

The electrochemical reduction of betamethasone valerate (BV) in a pharmaceutical formulation containing neomycin has been carried out in Britton-Robinson buffer (BRB) (0.04 mol L(-1)) by differential-pulse polarography (DPP). BV exhibits a well-defined irreversible reduction peak at -1.03 V/ref. The influence of pH on the reduction of BV was studied in Britton-Robinson buffer (pH range 1.7-10). A method for the analysis of BV in BRB (0.04 mol L(-1)), which allows quantification over the range 3.9x10(-6)-1.1x10(-4) mol L(-1), was proposed and successfully applied to the determination of BV in tablets with mean recovery and relative standard deviation of 100.81% and 0.45%, respectively.     

Determination of hesperidin and synephrine in Pericarpium Citri Reticulatae by capillary electrophoresis with electrochemical detection

A method based on capillary electrophoresis with electrochemical detection (CE-ED) has been developed for the determination of hesperidin (HP) and synephrine (SP) in the Chinese traditional herbal drug, Pericarpium Citri Reticulatae, the dried rind of the ripe fruits of Citrus reticulata Blanco (mandarin orange). The effects of some important factors such as the acidity and concentration of running buffer, separation voltage, and detection potential were investigated to determine the optimum conditions. The working electrode was a 300 microm diameter carbon disc electrode positioned opposite the outlet of the capillary. Both analytes could be well separated within 5 min in a 40 cm long capillary at a separation voltage of 12 kV in 50 mmol L(-1) borate buffer (pH 9.0). Excellent linearity was observed for the dependence of peak current on analyte concentration in the range from 2.5 x 10(-6) to 1.0 x 10(-3) mol L(-1) for SP and from 5.0 x 10(-6) to 1.0 x 10(-3) mol L(-1) for HP. The detection limits (S/N=3) for SP and HP were 4.96 x 10(-7) mol L(-1) and 6.54 x 10(-7) mol L(-1), respectively. This method has been successfully applied for the analysis of real samples, with satisfactory results.     

Polarographic determination of total iron content using a Fe(2+/3+)-Methylthymol Blue-NO2- system.

In the buffer solution of NH3-NH4Cl (pH = 8.5, 0.04 mol l(-1)), iron-Methylthymol Blue (MTB) can produce a sensitive polarographic wave at -1.10 V (vs. SCE) in the NaNO2. The peak current is linear with the concentration of the iron in the range of 3 x 10(-8)-5 x 10(-6) mol l(-1), and the detection limit is 1 x 10(-8) mol l(-1). By studying the characteristics of the wave and the electrode reaction mechanism, we can prove that the catalytic wave is an adsorption wave and that the peak current comes from the reduction of Fe(II). The molar ratio of iron to ligand was found to be 1:1. Adsorption particles are neutral molecules, the saturated adsorption quantity of the complex on the mercury electrode is 1.92 x 10(-9) mol cm(-2), according with the Frumkin isothermal formula. In the experiments, the adsorption coefficient (beta) is 4.05 x 10(5); the adsorption factor (gamma) is 0.70: the electron transfer number (n) is 2; the free energy (deltaG(o)) is 31.99 kJ mol(-1); the transfer coefficient of the irreversible adsorption is 0.42-0.45; and the reaction velocity constant (Ks) is 1.35 s(-1). This method, whose result is satisfying, can be applied to the detection of trace total iron contents in medicinal products.     

美洛昔康的单扫示波极谱法

在ＨＡｃ－ＮａＡｃ（ｐＨ４．７６）底液中,用单扫示波极谱法可以得到一个灵敏的美洛昔康二阶导数还原峰,其峰电位Ｅｎｐ＝－１．２８Ｖ（ｖｓ．ＳＣＥ）。峰电流与美洛昔康 度在９．０＊１０＾－８－６．０＊１０＾－６ｍｏｌ／Ｌ范围内呈线性关系（ｒ＝０．９９９４）检出限为３．０＊１０＾－８ｍｏｌ／Ｌ。该法应用于片剂中美洛昔康含量的测定,结果令人满意。     

Fluorimetric determination of peroxynitrite based on an enzymatic reaction.

A novel fluorimetric method for the determination of peroxynitrite (ONOO-) using hemoglobin (Hb) as a catalyst is described. The method employs the reaction of ONOO with thiamine (TM), a colorless, non-fluorescent reagent in a glycine-NaCl-NaOH buffer solution (pH 12.7), to generate a highly fluorescent product, thiochrome (TC). The fluorescent product was monitored by fluorimetry. A linear calibration graph was obtained over an ONOO- concentration range from 4.95 x 10(-7) mol L(-1) to 2.97 x 10(-5) mol L(-1), with a detection limit of 9.78 x 10(-9) mol L(-1) ONOO-. The relative standard deviation at an ONOO- concentration of 2.11 x 10(-6) mol L(-1) was 4.15% (n = 9).     

Oil-in-water emulsions as suitable working media for the direct polarographic determination of aziprotryne and desmetryne from its organic extracts in water samples

The electroanalytical behavior of the reduction of the herbicides aziprotryne (2-azido-4-isopropylamino-6-methylthio-1,3,5-triazine) and desmetryne (4-isopropylamino-6-methylamino-2-methylthio-1,3,5-triazine) in oil-in-water emulsions is reported. This medium allows the differential pulse polarographic determination of these s-triazines directly from their sample extracts in an appropriate organic solvent. Sodium pentanesulfonate was chosen as the most suitable surfactant to be used as emulsifying agent, whereas ethyl acetate was selected as the organic solvent to form the emulsions. The peak current was maximum in a 0.3 mol L(-1) HClO4 medium of the continuous aqueous phase for aziprotryne, and at pH 3.0 for desmetryne, and the potential became more negative as the pH increased for both herbicides. The limiting current is diffusion controlled and the electrode process is irreversible. Four electrons are involved in the overall electrochemical reduction process as determined by controlled potential coulometry, whereas the alpha n(a) values suggested that two electrons are involved in the rate-determining step. Using differential pulse polarography, aziprotryne and desmetryne can be determined in the emulsified medium over the concentration ranges 1.0 x 10(-7)-1.0 x 10(-4) mol L(-1), with limits of detection of 4.5 x 10(-8) mol L(-1) and 6.6 x 10(-8) mol L(-1), respectively. The method was applied to the determination of aziprotryne and desmetryne in spiked irrigation water. At concentration levels of 6.0 x 10(-7) mol L(-1) aziprotryne and 4.0 x 10(-7) mol L(-1) desmetryne, recoveries of 94 +/- 3% and 94 +/- 4%, respectively, were obtained after preconcentration on Sep-Pack C18 cartridges. Finally, partial least-squares regression (PLSR) has been used for treatment of the polarographic data obtained from mixtures of aziprotryne, desmetryne and simazine in oil-in-water emulsions. The size of the calibration set was of 29 samples by ninety two current measurements at different potentials. Prediction of the herbicides concentration within the range 1.0 x 10(-6)-1.0 x 10(-5) mol L(-1) was possible.     

锡(Ⅳ)-3,4-二羟基苯甲酸-钒(Ⅳ) 体系极谱吸附催化波的研究

在含有 3.6×10-3mol/L 的 VOSO4、6.0×10-5mol/L 的 3,4-二羟基苯甲酸(DHBA)、 0.1mol/L 的甲酸盐缓冲溶液(pH3.3)体系中,Sn(Ⅳ)-DHBA 络合物产生一灵敏的吸附平行催化波,峰电位在 -0.52 V(vs.SCE).二次导数波高与锡浓度在 3.4×10-10～5.1×10-7mol/L 范围内呈良好线性关系.检出限达浓度 2×10-10mol/L .研究了催化波的性质和电极反应机理.方法已应用于罐头食品中微量锡的测定.     

Speciation of Co(II), Co(III), and Cu(II) in ethylenediamine solutions by capillary electrophoresis

A capillary electrophoretic (CE) method for the speciation of Co(II), Co(III), and Cu(II) in electroless copper-plating baths containing ethylenediamine (En) has been developed. The method is based on the selective pre-capillary derivatization of Co(II) with 1,10-phenanthroline (Phen) followed by CE separation of stable [CoPhen(3)](2+), [CoEn(3)](3+), and [CuEn(2)](2+) chelates. The proposed derivatization procedure protects Co(II) from oxidation by dissolved oxygen and enables rapid determination of all three metal species within a single run. The optimized separations were carried out in a fused silica capillary (57 cmx75-microm I.D.) filled with an ethylenediamine sulfate electrolyte (20 mmol L(-1) H(2)SO(4), pH 7.0 with En, applied voltage +30 kV) using direct UV detection at 214 nm. The detection limits for a signal-to-noise ratio of 3 and 10 s, hydrodynamic injections were 5x10(-6) mol L(-1) for Cu(II), 1x10(-6) mol L(-1) for Co(III), and 4x10(-7) mol L(-1) for Co(II). Application of the method to the speciation of Co(II), Co(III), and Cu(II) in copper-plating bath samples is also demonstrated.