All-solid-state ion-selective electrodes with ion-to-electron transducers for dopamine determination

The electrically conducting polymers — polyaniline and originally synthesized poly(N-phenylglycine) — have been used as ion-electron transducers for new all-solid-state ion-selective membrane electrodes (ISEs) intended for the determination of dopamine. The properties of the new ISEs are evaluated, including the slope of the electrode characteristic, the linear range of the potential versus pC response, the effect of pH, and the response time. The results of chronopotentiometric measurements show that the new ISEs possess highly stable characteristics. The selectivity coefficients with respect to some foreign ions are determined. A method for potentiometric determination of dopamine using the new ISEs is developed. __________ Translated from Khimiko-Farmatsevticheskii Zhurnal, Vol. 40, No. 6, pp. 44–46, June, 2006.     

Stability-indicating electrochemical methods for the determination of meclophenoxate hydrochloride and pyritinol dihydrochloride using ion-selective membrane electrodes

The construction and electrochemical response characteristics of polyvinyl chloride (PVC) membrane sensors for the determination of meclophenoxate hydrochloride (I) and pyritinol dihydrochloride (II) in presence of their degradation products are described. The sensors are based on the use of the ion-association complexes of (I) and (II) cation with sodium tetraphenyl borate and ammonium reineckate counteranions as ion-exchange sites in the PVC matrix. In addition beta-cyclodextrin (beta-CD) membranes were used in the determination of I and II. These ion pairs and beta-CD were then incorporated as electroactive species with ortho nitrophenyl octyl ether (oNPOE) as a plasticizer. Three PVC sensors were fabricated for each drug, i.e. meclophenoxate tetraphenyl borate (meclo-TPB), meclophenoxate reineckate (meclo-RNC) and meclophenoxate beta-cyclodextrin (meclo-beta-CD), and the same was done for pyritinol (pyrit-TPB), (pyrit-RNC) and (pyrit-beta-CD). They showed near Nernestian responses for meclophenoxate over the concentration range 10(-5)-10(-2) with slopes of 52.73, 51.64 and 54.05 per concentration decade with average recoveries of 99.92+/-1.077, 99.96+/-0.502 and 100.03+/-0.763 for meclo-TPB, meclo-RNC and meclo-beta-CD respectively. Pyritinol also showed near Nernestian responses over the concentration range of 3.162 x 10(-6) - 3.162 x 10(-4) for pyrit-TPB and pyrit-RNC, and 10(-6) - 3.162 x 10(-4) for pyrit-beta-CD with slopes of 30.60, 31.10 and 32.89 per concentration decade and average recoveries of 99.99+/-0.827, 100.00+/-0.775 and 99.99+/-0.680 for pyrit-TPB, pyrit-RNC and pyrit-beta-CD respectively. The sensors were used successfully for the determination of I and II in laboratory prepared mixtures with their degradation products, in pharmaceutical dosage forms and in plasma.     

Simultaneous determination of levodopa, carbidopa, 3-O-methyldopa and dopamine in plasma using high-performance liquid chromatography with electrochemical detection

An analytical method is described which allows a fast, reliable and precise determination of levodopa and its metabolises 3-O-methyldopa and dopamine, as well as the peripheral aromatic amino acid decarboxylase inhibitor carbidopa, in a single 1 ml plasma sample of Parkinsonian patients. The compounds are quantitatively isolated on small Sephadex G-10 columns and determined by HPLC with electrochemical detection. Dihydroxybenzylamine or alpha-methyldopa are used as the internal standard. An example of therapeutic drug monitoring in a patient with fluctuations in motor performances is given. It is confirmed that interference with absorption of levodopa from the stomach by food can be partly responsible for these observed fluctuations.     

基于复合纳米微粒修饰丝网印刷电极的对乙酰氨基酚检测用电化学生物传感器

目的:构建一种复合纳米微粒修饰丝网印刷电极(SPCEs)的对乙酰氨基酚(ACOP)检测用电化学生物传感器(SPCEs/Au/GS/β-CD),建立ACOP测定方法。方法:采用化学镀方法于SPCEs表面形成纳米金颗粒(Au),然后将石墨烯(GS)和β-环糊精(β-CD)组成的复合物涂覆于SPCEs/Au表面,构建SPCEs/Au/GS/β-CD电极,采用扫描电镜(SEM)表征化学镀金、GS和电极的制备过程,采用循环伏安(CV)法和示差脉冲伏安(DPV)法研究ACOP的电化学性质。结果:在优化的实验条件下,ACOP浓度与DPV氧化峰电流(Ipa)在3.0×10-9～5.0×10-6 mol.L-1之间呈线性关系,线性相关系数为0.9990,检出限为1.6×10-9 mol.L-1。结论:该传感器灵敏快速、制备容易、样品用量少、可抛弃、抗干扰性强,有望用于痕量ACOP的检测。     

多巴胺在聚变色酸2B膜电极上的电化学行为及其测定

目的:研究多巴胺(DA)在聚变色酸2B 膜(PCR2B)修饰电极上的伏安行为,建立测定 DA 含量的差示脉冲伏安法。方法:采用循环伏安法研究 DA 在膜修饰电极上的电化学行为,以差示脉冲伏安(DPV)对其含量进行测定。结果:聚变色酸2B 膜修饰电极对 DA 有明显的电催化作用。在 pH 5.0磷酸盐缓冲液(PBS)中,氧化峰电流与 DA 浓度在2.0×10~(-6)～1.0×10~(-5)mol·L~(-1)范围内呈良好的线性关系,检测限为3.2×10~(-7)mol·L~(-1)。结论:该修饰电极可有效消除针剂中其他组分对 DA测定的干扰,可用于实际样品中 DA 含量的直接测定。     

In vivo electrochemical determination of extracellular dopamine in the caudate of freely-moving rats after a low dose of ethanol

Low doses of ethanol (i.e. less than 1 g/kg) elicit behavioral stimulation, control discriminative performance and mediate reinforcement in rats. These effects are thought to be mediated through central dopaminergic neuronal systems. In the present study, dopamine and serotonin/uric acid release from caudate was measured by in vivo voltammetry in freely-moving, unanesthetized rats after administration of a low dose of ethanol (600 mg/kg, IP). Within 15 min after a single ethanol administration, extracellular dopamine levels significantly increased in caudate, peaking at 35 min, and returning to baseline by 75 min. In addition, ethanol caused an attenuation of a second voltammetric signal that correlates with extracellular serotonin/uric acid concentrations, and this effect persisted through the course of the experiments. These neurochemical changes may underlie behavioral responses found after low doses of ethanol.     

Study of electrochemical oxidation and determination of albendazole using a glassy carbon-rotating disk electrode

In this work, electrochemical oxidation of albendazole (ABZ) was carried out using a glassy carbon-rotating disk electrode. Development of electroanalytical methodology for ABZ quantification in pharmaceutical formulations was also proposed by using linear sweep voltammetric technique. Electrochemical oxidation is observed for ABZ at E(1/2)=0.99 V vs. Ag/AgCl(sat), when an anodic wave is observed. Kinetic parameters obtained for ABZ oxidation exhibited a standard heterogeneous rate constant for the electrodic process equal to (1.51+/-0.07) x 10(-5) cm s(-1), with a alphan(a) value equal to 0.76. Limiting current dependence against ABZ concentration exhibited linearity on 5.0 x 10(-5) to 1.0 x 10(-2) mol l(-1) range, being obtained a detection limit of 2.4 x 10(-5) mol l(-1). Proposed methodology was applied to ABZ quantification in pharmaceutical formulations.     

Liquid chromatographic determination of guanethidine salts and hydrochlorothiazide using electrochemical detection and ion-pair techniques

A high-performance liquid chromatographic method with amperometric detection utilizing oxidation at the glassy carbon electrode is reported for the quantitative determination of a guanethidine (1)-hydrochlorothiazide (2) mixture. The drug mix is difficult to analyze by a single assay procedure due to large differences in the chemistry and chemical structure of the compounds. The drugs are best separated on an octadecylsilane column using 30:70 acetonitrile:0.05 M aqueous sodium dihydrogen phosphate containing 0.02 M sodium pentanesulfonate (pH 2.5) as the mobile phase at a 1.0 mL/min flow rate. Using a cell potential of +1300 mV versus Ag/AgCl and procaine hydrochloride as the internal standard, calibration curves were established for 1 monosulfate or sulfate and 2 in the 0.5-10 and 1.25-25 micrograms/mL range, respectively. Accuracy and precision of the assay are in the 1.7-6% range. The procedure is shown applicable to the analysis of a combination dosage form and is also useful for either drug in a single component dosage form.     

Differential effects of dopamine and psychoactive drugs on dopamine transporter phosphorylation and regulation

The dopamine transporter (DAT) is a phosphoprotein whose activity and phosphorylation state are acutely regulated by both protein kinase C (PKC) and substrate transport. DAT is a major site of action for psychostimulant and therapeutic drugs that either block transport or are transported substrates, but the effects of such drugs on DAT phosphorylation and regulation are not well understood. To examine these issues we subjected rDAT LLC-PK(1) cells to acute in vitro pretreatments with the endogenous, psychostimulant, and therapeutic compounds dopamine (DA), (-)-cocaine, 2 beta-carbomethoxy-3beta-(4-fluorophenyl)tropane (beta-CFT), GBR 12909, mazindol, and methylphenidate (MPH), in the presence or absence of the PKC activator phorbol 12 myristate 13 acetate (PMA), followed by analysis of DAT metabolic phosphorylation and transport activity. Basal phosphorylation of DAT was not affected by any of the uptake blockers tested, and PMA-stimulated phosphorylation was not affected by cocaine, beta-CFT, mazindol or MPH, but was strongly suppressed by GBR 12909. Pretreatment of cells with cocaine or MPH had no effect on subsequent DA transport activity or the extent of PMA-induced transport down-regulation, whereas GBR 12909 inhibited PMA-induced DAT internalization. These findings indicate that these DAT phosphorylation and down-regulation properties are unaffected by some classes of uptake blocking drugs, but that differential regulatory effects may be exerted by GBR compounds. Pretreatment of cells with DA had no obvious effect on basal or PMA-stimulated DAT phosphorylation but led to cocaine-blockable transport down-regulation. DA-induced down-regulation was blocked by the PKC inhibitor bisindoylmaleimide I and was not additive with down-regulation induced by PMA, consistent with PKC serving as a common step and point of integration for these DA and PMA induced processes. The results of this study provide information on the potential for endogenous and psychoactive compounds to modulate or be modulated by DAT phosphorylation-mediated regulatory mechanisms that may contribute to drug behavioral or therapeutic properties.     

Trace iron determination in aminoisophthalic acid using differential-pulse cathodic stripping voltammetry at carbon paste electrodes

Application of differential-pulse cathodic stripping voltammetry using a carbon paste electrode (consisting of carbon powder and liquid paraffin) have been investigated for trace determination of iron in 5-aminoisophthalic acid (AIPA). Samples were dissolved in 1 M HCl, pH was adjusted to 4–5 after addition of EDTA. Voltammetric measurements were performed after filtration. No sample decomposition (mineralization) was necessary. The method showed a good linearity between current and concentration from 3×10⁻⁷ to 5×10⁻⁵ mol dm⁻³ of iron, with a detection limit of 3×10⁻⁷ mol dm⁻³ (resp. 1 ppm in solid AIPA). The results agreed well to those obtained by atomic absorption spectrometry (AAS) using electrothermic atomisation. For AAS measurement, however, microwave digestion of samples was necessary.     

Differential regional effects of methamphetamine on dopamine transport

Multiple high-dose methamphetamine administrations cause long-lasting (>1 week) deficits in striatal dopaminergic neuronal function. This stimulant likewise causes rapid (within 1 h) and persistent (at least 48 h) decreases in activities of striatal: 1) dopamine transporters, as assessed in synaptosomes; and 2) vesicular monoamine transporter -2 (VMAT-2), as assessed in a non-membrane-associated (referred to herein as cytoplasmic) vesicular subcellular fraction. Importantly, not all brain areas are vulnerable to methamphetamine-induced long-lasting deficits. Similarly, the present study indicates that methamphetamine exerts differential acute effects on monoaminergic transporters according to brain region. In particular, results revealed that in the nucleus accumbens, methamphetamine rapidly, but reversibly (within 24 h), decreased plasmalemmal dopamine transporter function, without effect on plasmalemmal dopamine transporter immunoreactivity. Methamphetamine also rapidly and reversibly (within 48 h) decreased cytoplasmic VMAT-2 function in this region, with relatively little effect on cytoplasmic VMAT-2 immunoreactivity. In contrast, methamphetamine did not alter either dopamine transporter or VMAT-2 activity in the hypothalamus. Noteworthy, the nucleus accumbens and hypothalamus did not display the persistent long-lasting striatal dopamine depletions caused by the stimulant. Taken together, these data suggest that deficits in plasmalemmal and vesicular monoamine transporter activity lasting greater than 24-48 h may be linked to the long-lasting dopaminergic deficits caused by methamphetamine and appear to be region specific.     

Polymeric membrane electrodes for selective determination of methiaden

Polyvinyl chloride matrix membrane ion-selective electrodes for the determination of methiaden hydrochloride based on the ion-pair of methiaden cation with tetraphenylborate anion were prepared using bis(2-ethylhexyl)sebacate, (electrode A), 2-nitrophenyl octyl ether (electrode B). 2-nitrophenyl dodecyl ether (electrode C) and 1-isopropyl-4-nitrobenzene (electrode D) as the membrane solvents. The electrodes exhibit near-Nernstian response in different concentration ranges, depending on the used membrane solvents. The basic analytical parameters of these electrodes were evaluated. The potentiometric titration method was used to determine methiaden hydrochloride with good precision and accuracy.     

Liquid chromatographic determination of residual hydrogen peroxide in pharmaceutical excipients using platinum and wired enzyme electrodes

Hydrogen peroxide (H₂O₂) is a chemically reactive reagent that can oxidize and degrade many pharmaceutical compounds under normal conditions. Unfortunately, H₂O₂ is often introduced into pharmaceutical excipients during manufacturing and it may significantly affect the chemical stability of drugs in formulations. Thus, a sensitive analytical method for determination of residual H₂O₂ in excipients is of importance in formulation development and product quality control. A liquid chromatographic system with a dual channel electrochemical detector (LCEC) was equipped with either a platinum electrode or a wired peroxidase electrode for determination of H₂O₂. The excipient (0.1 g) was dissolved in 10 ml of mobile phase and 5 μl of the dissolved solution was directly injected. The chromatographic run time for each sample was 1 min with a detection limit of 10 ng/ml (S/N=5) using the platinum electrode and 1 ng/ml (S/N=5) using the wired enzyme coated electrode, respectively. The peak purity was assured by comparing the peak ratios at different potentials for both the standard and the samples. The H₂O₂ levels in different batches of PVP, PEG, and other surfactants from different manufacturers were determined and the values ranged from 0 to 244 ppm. The LCEC method is exceptionally fast, accurate and convenient for quantitation of low levels of residual H₂O₂ in pharmaceutical formulation excipients.     

A zucchini-peroxidase biosensor applied to dopamine determination

A biosensor modified with peroxidase from crude extract of zucchini (Cucurbita pepo) was developed for the determination of dopamine in pharmaceutical samples. This enzyme catalyses the oxidation of dopamine to dopaminequinone, in presence of hydrogen peroxide, which the electrochemical reduction can be followed at a peak potential of -0.02 V. The recovery of dopamine from the samples ranged from 94.8% to 106% and a rectilinear analytical curve for dopamine concentration from 5.0 x 10(-4) to 3.0 x 10(-3) mol L-1 (r=0.9982) was obtained. The detection limit was 2.6x10(-5) mol L-1 and the relative standard deviation was less than 1.2% for 7.9 x 10(-4) mol L-1 dopamine in 0.1 mol L-1 phosphate buffer solution at pH 6.0 (n=10).