Characterization of ceramic ion-selective membrane-electrodes-I The Ag(2)S electrode

The behaviour of a new type of electrode, made from ceramic Ag(2)S, has been investigated. The electrode response is Nernstian for Ag(+) over the range 10(-6)-2M and for Hg(2+) in the concentration range 10(-6)-10(-2)M, both at constant ionic strength (0.1M). The electrode is Ag(+)-selective, with maximum interference from Hg(2+). It can be used for acid-base potentiometric titration and for potentiometric Ag(+) and Hg(2+) precipitation titrations.     

Electrocatalytic oxidation of NADH based on polyluminol and functionalized multi-walled carbon nanotubes

This work presents that the electrocatalytic oxidation of NADH can be enhanced by the hybrid composites of polyluminol and functionalized multi-walled carbon nanotubes (MWCNTs). The hybrid composites can be easily prepared by the electropolymerization of luminol and the adsorption of functionalized MWCNTs. The modified electrode exhibits two redox couples which can show two electrocatalytic peaks at about 0.1 and 0.3 V (vs. Ag/AgCl) to NADH oxidation. The kinetic constant, k(kin), for the electrocatalytic oxidation of NADH, evaluated by chronoamperometry and voltammetry using a rotating disk electrode (RDE), provided values close to 10(5) M(-1) s(-1). At an applied potential of 0.1 V, the sensor provides a linear response range for NADH from 5 × 10(-6) up to 1.5 × 10(-4) M with a sensitivity of 183.9 μA mM(-1) cm(-2), and detection and quantification limits of 0.6 and 5 μM (S/N = 3), respectively.     

Selectivity of solid-contact Ag potentiometric sensors based on thiacalix[4]arene derivatives

Potentiometric sensors based on glassy carbon electrode covered with polyaniline and thiacalix[4]arenes containing amidopyridine, morpholide, pyrrolidide and hydrazide functional groups in cone, partial cone and 1,3-alternate conformations have been developed and applied for determination of Ag(+) ions in the range from 1.0 x 10(-2) to 4.0 x 10(-7)M and limits of detection from 1 x 10(-7) to 3.5 x 10(-8)M. The sensitivity of Ag(+) detection decreases in the following range of thiacalix[4]arene substituents: morpholide>pyrrolidide>amidopyridine>hydrazide. Potentiometric selectivity coefficients predominantly showed binding of Ag(+), Hg(II) and Fe(III) ions over other transient and alkali metals. The influence of functional groups and conformation of receptor on the selectivity of the sensor response was investigated. As shown, selectivity and sensitivity of Ag(+) determination depends on the steric accessibility of the binding site and flexibility of the receptor structure. For Fe(III) ions, changes of the sensor potential are also determined by their implementation in redox reactions of polyaniline.     

Construction and performance characterization of screen printed and carbon paste ion selective electrodes for potentiometric determination of naphazoline hydrochloride in pharmaceutical preparations

This paper describes the development of screen-printed (SPE) and carbon paste (CPE) sensors for the rapid and sensitive quantification of naphazoline hydrochloride (NPZ) in pharmaceutical formulations. This work compares the electroactivity of conventional carbon paste and screen-printed carbon paste electrodes towards potentiometric titration of NPZ. The repeatability and accuracy of measurements performed in the analysis of these pharmaceutical matrices using new screen printed sensors were evaluated. The influence of the electrode composition, conditioning time of the electrode and pH of the test solution, on the electrode performance were investigated. The drug electrode showed Nernstain responses in the concentration range from 1 × 10(-6) to 1 × 10(-2) mol L(-1) with slopes of 57.5 ± 1.3 and 55.9 ± 1.6 mV per decade for SPE and CPE, respectively, and was found to be very precise and usable within the pH range 3-8. These sensors exhibited a fast response time (about 3 s for both SPE and CPE, respectively), a low detection limit (3.5 × 10(-6) and 1.5 × 10(-6) M for SPE and CPE, respectively), a long lifetime (3 and 2 months for SPE and CPE, respectively) and good stability. The selectivity of the electrode toward a large number of inorganic cations, sugars and amino acids was tested. It was applied to potentiometric determination of NPZ in pure state and pharmaceutical preparation under batch conditions. The percentage recovery values for the assay of NPZ in tablets (relative standard deviations ≤0.3% for n = 4) were compared well with those obtained by the official method.     

Used gold nano-particles as an on/off switch for response of a potentiometric sensor to Al(III) or Cu(II) metal ions

The potentiometric response of a carbon paste electrode modified with silica sol-gel and mercaptosuccinic acid (MSA) in the presence and absence of gold nano-particles was studied. The results showed that the electrode with gold nano-particles was responded to Al(3+) ions as a hard metal ion. On the other hand, the electrode without gold nano-particles was responded to copper ions as a soft metal ion. The electrodes without and with gold nano-particles exhibits a Nernstian slope of 29.1 and 19.2 mV decade(-1) for copper and aluminum ions over a wide concentration range of 4.3×10(-7)-1.0×10(-2) and 4.5×10(-7)-1.6×10(-3) mol L(-1), respectively. The detection limits of electrodes were 4.0×10(-7) and 1.6×10(-7) mol L(-1) for copper and aluminum ions, respectively.     

六氰合铁酸铜钴-多壁碳纳米管修饰电极研究

采用电沉积方法制备六氰合铁酸铜钴-多壁碳纳米管复合修饰电极(CuCoHCF-MWCNTs/GCE).研究碳纳米管用量、电解液组成对该修饰电极性能的影响.结果表明,与单一的六氰合铁酸铜钴薄膜修饰电极相比,六氰合铁酸铜钴-多壁碳纳米管复合修饰电极具有更优良的电化学特性,以其催化氧化过氧化氢,峰电流与过氧化氢浓度在3.16×10-5～2.92×10-3mol·L-1范围内呈良好的线性关系,线性回归方程为ip(μA)=0.5529+1.1299C(×10-4mol·L-1),相关系数r=0.9966,检出限为1.75×10-5mol·L-1.     

石墨烯修饰玻碳电极测定邻苯二酚

制备了用于测定邻苯二酚(CAT)的石墨烯修饰电极,并应用循环伏安法研究了CAT在该修饰电极上的电化学行为;用差分脉冲伏安法研究了测试底液的pH值对该修饰电极性能的影响,结果表明,此修饰电极在含不同浓度CAT的PBS溶液(pH=7.0)中测定,响应电流与CAT浓度在5.0×10-8～5.6×10-4mol/L范围内有良好的线性关系,相关系数r=0.9919,检出限为6.68×10-9mol/L(S/N=3)。与其它几种修饰电极相比,石墨烯修饰电极制备简单、响应时间快、操作简便,稳定性和重现性良好,有应用价值。     

Application of an Hg2+ selective imprinted polymer as a new modifying agent for the preparation of a novel highly selective and sensitive electrochemical sensor for the determination of ultratrace mercury ions

A simple and very selective electrode, based on a mercury ion imprinted polymer (IIP), and its application for the determination of Hg(2+) ions in the real samples is introduced. Mercury ion selective cavities were created in the vinyl pyridine based cross-linked polymer. In order to fabricate the sensor carbon particles and polymer powder were mixed with melted n-eicosane. An explicit difference was observed between the responses of the electrodes modified with IIP and non imprinted polymer (NIP), indicating proper performance of the recognition sites of the IIP. Various factors, known to affect the response behavior of selective electrode, were investigated and optimized. The interference of different ionic species with the response of the electrode was also studied. The results revealed that, compared to previously developed mercury selective sensors, the proposed sensor was more selective, regarding the common potential interferer. This sensor showed a linear response range of 2.5 × 10(-9)-5.0 × 10(-7) M and lower detection limit of 5.2 × 10(-10) M (S/N). The sensor was successfully applied to the determination of mercury in real samples.     

Potentiometric determination of silver(I) by selective membrane electrode based on derivative of porphyrin.

The performance of silver metal complexes with meso-tetraphenylporphyrin ([H2T(4-CH3)]PP) as ionophores for ion-selective electrodes was studied. The electrode exhibited linear response with Nernstian slope of 59.2 +/- 1.0 mV per decade within the concentration range of 1.0 x 10(-7)-1.0 x 10(-1) M silver ions. The limit of detection as determined from the intersection of the extrapolated linear segments of the calibration plot, was 1.0 x 10(-7) M. The response time of the electrode was < 10 s over the entire concentration range. The silver-selective electrode exhibited good selectivity for Ag(I) with respect to alkali, alkaline earth and heavy metal ions. The electrodes could be used at least three months without a considerable divergence in their potential. The electrodes are suitable for use in aqueous solutions in a wide pH range of 3.0-9.0. They were used as indicator electrodes in titration of Ag(I) with sodium iodide solution and were successfully applied to direct determination of silver in real samples.     

Electrochemical sensor for neurotransmitters at physiological pH using a heterocyclic conducting polymer modified electrode

We report the simultaneous determination of two neurotransmitters, norepinephrine (NEP) and serotonin (5-HT), at physiological pH using the electropolymerized film of 3-amino-5-mercapto-1,2,4-triazole modified glassy carbon (p-AMTa) electrode. A bare glassy carbon (GC) electrode fails to resolve the voltammetric signals of NEP and 5-HT due to the surface fouling caused by the oxidized products of them. However, the p-AMTa electrode not only separates the voltammetric signals of NEP and 5-HT with a potential difference of 150 mV between NEP and 5-HT but also shows higher oxidation currents for them. The simultaneous determination of NEP and 5-HT was successfully achieved at p-AMTa electrode using differential pulse voltammetry method. The amperometric current response increased linearly with increasing NEP and 5-HT concentration in the range of 1.0 × 10(-8) to 1.0 × 10(-4) M and 1.0 × 10(-8) to 5.0 × 10(-5) M, respectively, and the detection limit was found to be 1.65 × 10(-11) for NEP and 1.32 × 10(-11) M for 5-HT (S/N = 3). The p-AMTa electrode shows better recovery results for spiked NEP and 5-HT in human blood plasma samples.     

Coated wire silver-ion selective electrode based on a N,N'-bis(2-thienylmethylene)-1,2-diaminobenzene.

A novel membrane coated platinum-wire electrode (MCPWE) based on N,N'-bis(2-thienylmethylene)-1,2-diaminobenzene (BTMD) for highly selective determination of Ag+ ion has been developed. The influences of membrane composition and pH on the potentiometric responses of electrode were investigated. The potentiometric responses are independent of the pH of the test solution in the range of 5.0 - 9.0. The electrode shows a linear response for Ag+ ion over the concentration range of 1.0 x 10(-60 to 1.0 x 10(-1) M with a lower detection limit of 6.0 x 10(-7) M. The electrode possesses a Nernstian slope of 59.7 mV decade(-1) and a fast response time of < or = 17 s and can be used for at least 2 months without any observable deviation. The proposed electrode displayed very good selectivity for Ag+ ion with respect to NH4+ and alkali, alkaline earth and some common transition metal ions. The practical utility of the electrode has been demonstrated by its use as the indicator electrode in the potentiometric titration of an AgNO3 solution with a NaI solution and in determination of the silver content of a developed radiological film.     

Amperometric determination of urea using an NADH-dependent coupled enzyme

Enzyme electrodes for the amperometric measurement of urea were prepared by co-immobilizing l-glutamate dehydrogenase and urease onto an Immobilon-AV affinity membrane with attachment to a glassy carbon electrode. Reduced nicotinamide adenine dinucleotide (NADH) was used as the electroactive species. The electrochemical oxidation of NADH was monitored at +1.0 V vs. Ag/AgCl. The enzyme immobilized electrode was linear over the range of 2.0 x 10(-5) to 2 x 10(-4)M. The response time of the electrode was 3 min and the optimum pH of enzyme immobilized membrane was pH 7.4-7.6 (Dulbecco's buffer solution). It was stable for at least two weeks and 50 assays. There were no interferences from other physiological material, except for high levels of ascorbic acid.     

Electrochemical behavior of o-sec-butylphenol at glassy carbon electrode modified with multiwalled carbon nanotubes and 1-butyl-3-methylimidazolium hexafluorophosphate

A sensitive electrochemical sensor based on immobilized multiwalled carbon nanotubes (MWCNTs) and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM·PF(6)) on a glassy carbon electrode (GCE) for o-sec-butylphenol (osBP) was proposed. The electro-oxidation behavior was studied, the experimental conditions were optimized and kinetic parameters were calculated. The results indicated that this electrochemical sensor has the advantages of fast electron-transfer rate, minimal fouling of electrodes, high sensitivity and stability for o-sec-butylphenol. Upon comparison with a glassy carbon electrode, this senor would effectively minimize the over-potential and increase the electrochemical response to o-sec-butylphenol. Under the optimum conditions, the peak current was linear to the osBP concentration range from 1 × 10(-7) to 2.5 × 10(-5) M with the detection limit of 8.65 × 10(-9) M (S/N = 3). The proposed method was applied to the determination of spiked water samples with satisfactory results.     

Selective electrodes for silver based on polymeric membranes containing cali

Silver ion-selective electrodes were prepared with polymeric membranes based on two calix[4]arene derivatives functionalized by two hydroxy and two benzothiazolylthioethoxy groups. The electrodes all gave a good Nernstian response of 58mV decade(-1) for silver in the activity range 5 x 10(-6)-10(-1) M, the limits of detection reached 10(-5.8) M and exhibited high selectivity towards alkali, alkaline earth and some transition metal ions. The electrode was used as indicator electrode in titrations of Ag+ with Cl- ion.     

Poly-glutamic acid modified carbon nanotube-doped carbon paste electrode for sensitive detection of L-tryptophan

A novel poly-glutamic acid (PGA) film modified carbon paste electrode (CPE) incorporating carbon nanotubes (CNTs) was first prepared for the determination of l-tryptophan (l-Trp). Scanning electron microscopy and Fourier transform infrared spectroscopy were applied for characterization of the surface morphology of the modified electrodes and cyclic voltammetry was used to investigate the electrochemical properties of the proposed electrode towards the oxidation of l-Trp. Optimization of the experimental parameters was performed with regard to pH, ratio of CNTs, concentration of glutamic acid, electro-polymerization cycles, accumulation time and concentration of sodium dodecylbenzene sulfonate. The linearity between the oxidation peak current and the l-Trp concentration was obtained in the range of 5.0×10(-8) to 1.0×10(-4)M with a detection limit of 1.0×10(-8)M (S/N=3) and the sensitivity was calculated to be 1143.79μA?mM(-1)?cm(-2). In addition, the PGA modified CPE incorporating CNTs displayed high selectivity, good stability and reproducibility, making it suitable for the routine analysis of l-Trp in clinical use.     

Direct electron transfer enhancement of covalently bound tyrosinase to glassy carbon via Woodward's reagent K

This work describes the reaction mechanism for chemical modification of tyrosinase by Woodward's Reagent K and its covalent attachment to a glassy carbon electrode. The spectrophotometric studies revealed that the modification does not cause a significant structural change to tyrosinase. The direct electrochemistry of modified enzyme was achieved after immobilization on an oxidatively activated glassy carbon electrode. The enzyme film exhibited a pair of well-defined quasi-revesible voltammetric peaks corresponding to the Cu (II)/Cu (I) redox couple located in the active site of tyrosinase. The formal potential of immobilized enzyme was measured to be 90mV (vs. Ag/AgCl) in phosphate buffer solution at pH 7.0. The charge-transfer coefficient and apparent heterogeneous electron transfer rate constant were estimated to be 0.5 and 0.9±0.06s(-1), respectively. Finally, the electrochemical behavior of the immobilized enzyme in the presence of caffeic acid and L-3,4-dihydroxyphenylalanine as substrates was investigated. The amperometric study of biosensor toward L-3,4-dihydroxyphenylalanine resulted a linear response in the concentration range from 1.66×10(-6) to 8.5×10(-5)M with detection limit of 9.0×10(-5)M and sensitivity of 135mAμM(-1)cm(-2).     

Application of multi-walled carbon nanotubes modified carbon ionic liquid electrode for electrocatalytic oxidation of dopamine

A simple, sensitive, and reliable method based on a multi-walled carbon nanotubes (MWNTs) modified carbon ionic liquid electrode (CILE) has been successfully developed for determination of dopamine (DA) in the presence of ascorbic acid (AA). The acid-treated MWNTs with carboxylic acid functional groups could promote the electron-transfer reaction of DA and inhibit the voltammetric response of AA. Due to the good performance of the ionic liquid, the electrochemical response of DA on the MWNTs/CILE was better than that of other MWNTs modified electrodes. Under the optimum conditions a linear calibration plot was obtained in the range 5.0×10(-8) to 2.0×10(-4) mol L(-1) and the detection limit was 1.0×10(-8) mol L(-1).     

Direct electrochemical behavior of cytochrome c on DNA-modified glassy carbon electrode and its application to cytochrome c biosensor.

DNA was immobilized on glassy carbon electrodes to fabricate DNA-modified electrodes. The direct electron transfer of horse heart cytochrome c on DNA-modified glassy carbon electrode was achieved. A pair of well-defined redox peaks of cytochrome c appeared at Epc = -0.017 V and Epa = 0.009 V (vs. Ag/AgCl) in 10 mM phosphate buffer solution (pH 7.0) at a scan rate of 50 mV/s. The electron transfer coefficient (alpha) and the standard rate constant of the surface reaction (Ks) of cytochrome c on DNA-modified electrodes could be estimated to be 0.87 and 34.52 s(-1), respectively. The DNA-modified glassy carbon electrode could be applied to detect cytochrome c by means of differential pulse voltammetry (DPV). The cathodic peak current was proportional to the quantity of cytochrome c in the range of 4.0 x 10(-6) M to 1.2 x 10(-5) M. The correlation coefficient is 0.996, and with the detection limit was 1.0 x 10(-6) M (three times the ratio of signal to noise, S/N = 3).     

阿拉伯糖基有序介孔碳修饰电极检测盐酸奈福泮的研究

以阿拉伯糖为碳源,介孔硅(SBA-15)为模板剂,用硬模板法制备有序介孔碳材料,采用场发射扫描电镜(Scanning Electron Microscopy,SEM)、透射电子显微镜(Transmission Electron Microscope,TEM)、全自动比表面及孔隙度分析仪(Brunner Emmet Te...     

Determination of melamine based on electrochemiluminescence of Ru(bpy)3(2+) at bare and single-wall carbon nanotube modified glassy carbon electrodes

The electrochemiluminescence (ECL) of Ru(bpy)(3)(2+) at bare and single-wall carbon nanotube (SWNT) modified glassy carbon (GC) electrodes has been employed for the determination of melamine for the first time, giving a linear response (R(2) = 0.99682) for melamine concentration from 1.0 × 10(-10) to 1.0 × 10(-5) M at a bare GC electrode in pH 10 borate buffer, and the detection limit is 1.0 × 10(-10) M. However, the detection limit can be reduced further to 1.0 × 10(-13) M after modification of the GC electrode by SWNTs. This is much lower compared to other detection methods. The proposed method was applied to the determination of melamine added to a commercial milk sample; the recovery is quite satisfactory with good reproducibility and stability. All of these results provide the possibility of developing a novel ECL detection method for melamine.