All-plastic, disposable, low detection limit ion-selective electrodes

A novel concept for all-plastic and all-solid-state ion-selective electrodes (ISEs) is introduced. Planar, flexible ion-selective electrodes, comprising only polymeric materials, with no internal solution, were obtained. The cast conducting polymer layer (obtained from aqueous suspension) was covered with a solvent polymeric based membrane to obtain a planar all-plastic sensor. The conducting polymer layer served both as electrical contact and as ion-to-electron transducer. To illustrate this concept, the conducting polymer poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) ions (PEDOT-PSS, Baytron P) was chosen. Due to interaction, analyte cations-poly(4-styrenesulfonate) anions, an extended linear range of potentiometric responses was obtained, with lowered detection limit.As example, Ca²⁺-selective and K⁺-selective all-plastic electrodes were fabricated and yielded with high selectivity, near Nernstian slopes and fast responses. The detection limits obtained for Ca²⁺- and K⁺-selective sensors were 5 × 10⁻⁹ M CaCl₂ and 4.4 × 10⁻⁷ M KCl, respectively.The possibilities of modifying the conducting polymer-phase composition is highlighted. This method is extremely useful to tune the desired type of responses, and cannot be directly applied for electrochemically deposited conducting polymers.     

Preparation and characterization of three-dimensionally ordered macroporous yttria-stabilized zirconia by aqueous organic gel route

Three-dimensionally ordered macroporous (3-DOM) yttria-stabilized zirconia (YSZ) was prepared by aqueous organic gel method through the interstitial spaces between polystyrene spheres assembled on glass substrates. The morphologies and pore size of the porous YSZ were characterized by scanning electron microscope (SEM) and nitrogen adsorption. The thermal behavior, the phase and chemical composition of PS/YSZ composite were investigated by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that porous YSZ has been formed with the pores arranged in an ordered close-packed three-dimensional structure. Ni/YSZ cermet was also prepared by immersing the 3-DOM YSZ into the solution of nickel nitrate and urea. The electrical conductivity of Ni/YSZ was about 400 S cm⁻¹ between 600 and 800 °C.     

三维有序大孔钙钛矿型氧化物LaFeO3的合成及甲烷化学链重整性能

采用无皂乳液聚合法制备了聚苯乙烯(PS)聚合物微球,并采用胶晶模板法制备了三维有序大孔3DOM LaFeO₃钙钛矿型氧化物.通过扫描电镜、X射线衍射和傅里叶变换红外光谱等手段对氧化物的性能进行了表征.利用程序升温还原和多次氧化还原循环反应评价了氧化物的反应性,并在固定床反应器上研究了其甲烷氧化性能.结果表明,与离心法和蒸发法相比,垂直沉积法获得的PS微球模板排列更均匀有序;前驱物溶剂及浓度对最终的三维有序大孔材料的结构有显著影响,利用乙醇为前驱物溶剂所制备的样品比利用乙烯为溶剂的样品具有更好的三维有序大孔结构,前驱物乙醇溶液浓度在1.0 mol/L为宜.甲烷氧化实验表明,3DOM-LaFeO₃钙钛矿型氧化物中存在两种氧物种:表面吸附氧和体相晶格氧.表面吸附氧主要在反应初期将甲烷完全氧化为CO₂和水蒸汽,而体相晶格氧主要将甲烷部分氧化为H₂和CO.在甲烷部分氧化反应中,三维有序大孔LaFeO₃钙钛矿型氧化物比相同质量的纳米LaFeO₃氧化物提供了更多的氧,并且可使甲烷在较宽的反应阶段生成H₂和CO摩尔比为2:1的合成气,从而更有利于后续的费托合成等工艺.     

三维有序结构的金掺杂纳米TiO_2修饰电极用于H_2O_2的测定

在ITO玻璃表面构建了三维有序多孔结构的金掺杂纳米Ti O2薄膜(3DOM GTD/ITO),同时制备了一种细胞色素c(Cyt c)酶生物传感器(Cyt c/3DOM GTD/ITO)。通过透射电镜(TEM)、扫描电镜(SEM)对修饰电极进行表征。紫外-可见光谱实验表明吸附在GTD上的Cyt c能够保持其生物活性,二级结构未被破坏。同时研究了Cyt c在3DOM GTD/ITO修饰电极表面的直接电化学及对H2O2的电催化行为。结果显示,Cyt c在3DOM GTD/ITO修饰电极上有显著的直接电化学响应,峰电流与扫描速度呈线性关系,说明该电极过程是表面电化学控制过程。Cyt c/3DOM GTD/ITO修饰电极对H2O2具有良好的催化性能,线性范围为3.0×10-7~1.70×10-5mol/L,检出限为3.6×10-8mol/L(S/N=3),响应时间为5 s,且该修饰电极具有较好的重现性和稳定性。     

Lead(II) ion-selective electrode based on polyaminoanthraquinone particles with intrinsic conductivity

A new polyvinylchloride membrane electrode was facilely prepared by using polyaminoanthraquinone (PAAQ) microparticles with an intrinsically electrical conductivity as a lead(II) ionophore. It is found that the electrode performance will significantly be improved with adding 1 wt% PAAQ microparticles and decreasing the membrane thickness. A 90 μm-thick membrane electrode consisting of PAAQ(salt):polyvinyl chloride:dioctylphthalate:sodium tetraphenylborate of 1:33:66:1 (wt) but without any traditional lead(II) ionophore achieved the optimal performance and exhibited a good Nernstian response for Pb(II) ions over a wide concentration range from 2.5 × 10⁻⁶ to 0.1 M with a slope of 28.9 mV/decade and a detection limit down to 776 nM. A reasonably short response time of 12 s was revealed together with a long lifetime over a period of around 4 months in a wide pH range between 2.8 and 5.2. A fixed interference method indicated that the electrode has an excellent selectivity for lead(II) ion over alkali, alkaline earth and other heavy metal ions. The proposed electrode has been also found to be a powerful indicator electrode for potentiometric titration of Pb(II) ions with EDTA. The electrode can be used to accurately monitor the Pb(II) pollution in environmental waters.     

Stripping voltammetric determination of silver(I) at carbon paste electrode modified with 3-amino-2-mercapto quinazolin-4(3H)-one

A differential pulse anodic stripping voltammetric method was developed for the determination of Ag(I) at a 3-amino-2-mercapto quinazolin-4(3H)-one modified carbon paste electrode. The analysis procedure consisted of an open circuit accumulation step in stirred sample solution for 12 min. This was followed by medium exchange to a clean solution where the accumulated Ag(I) was reduced for 15 s in −0.6 V. Subsequently an anodic potential scan was effected from −0.2 to +0.2 V to obtain the voltammetric peak. The detection limit of silver(I) was 0.4 μg L⁻¹ and R.S.D. for 10, 100 and 200 μg L⁻¹ silver(I) were 2.4, 1.8 and 1.3%, respectively. The calibration curve was linear for 0.9-300 μg L⁻¹ silver(I). Many coexisting ions had little or no effect on the determination of silver(I). The procedure was applied to determination of silver(I) in X-ray photographic films and natural waters. In X-ray photographic film samples, the results have compared to those obtained by atomic absorption spectroscopy.     

The influence of X-ray resonant Raman scattering effects on the detection of copper(II) tetrasulphonated phthalocyanine (CuTSPc) thin-films deposited on gold electrodes

The influence of X-ray resonant Raman scattering on the detection capabilities of copper(II) tetrasulphonated phthalocyanine (CuTSPc) thin-films on gold electrodes has been investigated by means of synchrotron radiation X-ray fluorescence. In particular the paper focuses on the influence of the excitation energy in the relative narrow energy region of 9.2 to 11.7 keV on the detection limits and the peak-to-background ratios of copper.     

Stripping voltammetric determination of trace amounts of mercury using a carbon paste electrode modified with 2-mercapto-4(3H)-quinazolinone

A carbon paste electrode modified with 2-mercapto-4(3H)-quinazolinone was used for the voltammetric determination of mercury(II). Mercury was preconcentrated onto the surface of the modified electrode only by the complexing effect of the modifier without application of potential (i.e. in open-circuit conditions). After exchange of the medium, the accumulated amount of mercury(II) was determined by differential pulse anodic stripping voltammetry. The response depended on the concentration of mercury in the bulk solution, preconcentration time, and other parameters. The detection limit was 0.1 g 1^–1 Hg(II) for a preconcentration time of 15 min. Preconcentration for suitable times yielded a linear calibration graph from 0.5 to 6000 g 1^–1 Hg(II). For multiple determinations (5 runs), the relative standard deviation was 5% for a concentration of 100 g 1^–1 Hg(II). The proposed procedure was used to determine trace mercury in plant and sewage sludge samples with good results.On leave from Hainan University, Hainan Peoples Republic of China     

Preparation of a carbon ceramic electrode modified by 4-(2-pyridylazo)-resorcinol for determination of trace amounts of silver

A 4-(2-pyridylazo)-resorcinol (PAR)-modified carbon ceramic electrode (CCE) prepared by the sol-gel technique has been reported for the first time in this paper. By immersing the CCE in aqueous solution of PAR (0.001 mol L⁻¹), after a short period of time, a thin film of PAR was rapidly formed on the surface of the electrode due to its strong adsorption properties. A differential pulse anodic stripping voltammetric (DPASV) method was developed for determination of Ag(I) at the modified carbon ceramic electrode. The analysis procedure consisted of an open circuit accumulation step in a sample solution which was continuously stirred for 12 min. This was followed by replacing the medium with a clean solution where the accumulated Ag(I) was reduced for 15 s in −0.6 V. Then, the potential was scanned from −0.2 to +0.2 V to obtain the voltammetric peak. The detection limit of silver(I) was 0.123 μg L⁻¹, and for seven successive determinations of 10, 100 and 200 μg L⁻¹ Ag(I), the relative standard deviations were 2.1, 1.4 and 1.03%, respectively. The calibration curve was linear for 0.5-300 μg L⁻¹ silver(I). The procedure was applied to determine silver(I) in X-ray photographic films and super-alloy samples.     

Voltammetric Properties of All‐solid State Ion‐selective Electrodes with Multiwalled Carbon Nanotubes‐poly(3‐octylthiophene‐2,5‐diyl) Nanocomposite Transducer

Voltammetric response of an all‐solid‐state ion‐selective electrode was studied on example of potassium‐selective sensor with poly(vinyl chloride) based membrane and nanocomposite transducer containing poly(3‐octylthiophene‐2,5‐diyl) and multiwalled carbon nanotubes. Factors limiting the rate of the electrochemical process and the response were discussed. The challenge in voltammetric applications of ion‐selective electrodes is thickness of the plastic membrane. It was found that although a relatively thick ion‐selective membrane was applied, as typically used in potentiometric studies, the position of the reduction peak, corresponding to potassium ions incorporation, was dependent on ions concentration in a Nernstian manner. This opens possibility of deviation from the paradigm of ultrathin membranes in voltammetric applications, thus potentially extending the sensors lifetime. The high resistance of the membrane did not affect the voltammetric characteristics, because the resistance was independent of ions concentration in solution. On the other hand, high resistance results in charge trapping effect in the solid contact material, leading to advantageous retention of the oxidized‐conducting state of the solid contact, independently of the applied electrode potential.     

A novel chemically modified carbon paste electrode based on a new mercury(II) complex for selective potentiometric determination of bromide ion

A new modified carbon paste electrode based on a recently synthesized mercury (II) complex of a pyridine containing proton transfer compound as a suitable carrier for Br⁻ ion is described. The electrode has a linear dynamic range between 3.00×10⁻² and 1.0×10⁻⁵ M with a near-Nernastian slope of 61.0±0.9 mV per decade and a detection limit of 4.0×10⁻⁶ M (0.32 ppm). The potentiometric response is independent of the pH of the solution in the pH range 4.0–8.3. The electrode possesses the advantages of low resistance, fast response and good over a variety of other anions. It was applied as an indicator electrode in potentiometric titration of bromide ions and for the recovery of Br⁻ from tap water.     

Electrochemical behavior and determination of fluphenazine at multi-walled carbon nanotubes/(3-mercaptopropyl)trimethoxysilane bilayer modified gold electrodes

A novel multi-walled carbon nanotubes/(3-mercaptopropyl)trimethoxysilane (MPS) bilayer modified gold electrode was prepared and used to study the electrochemcial behavior of fluphenazine and determine it. Fluphenazine could effectively accumulate at this electrode and produce two anodic peaks at about 0.78 V and 0.93 V (versus SCE). The peak at about 0.78 V was much higher and sensitive, thus it could be applied to the determination. Various conditions were optimized for practical application. Under the selected conditions (i.e. 0.05 M pH 3.5 HCOOH-HCOONa buffer solution, 5 μl 1 mg ml⁻¹ multi-walled carbon nanotubes for Φ=2.0 mm electrode, accumulation at open circuit for 180 s), the anodic peak current was linear to fluphenazine concentration in the range from 5×10⁻⁸ to 1.5×10⁻⁵ M with correlation coefficient of 0.9984, the detection limit was 1×10⁻⁸ M. For a 1×10⁻⁵ M fluphenazine solution, the relative standard deviation of peak current was 2.51% (n=8). This method was successfully applied to the determination of fluphenazine in drug samples and the recovery was 96.4-104.4%. The electrode could be easily regenerated and exhibited some selectivity, but some surfactants reduced the peak current greatly. The modified electrode was characterized by alternating current impedance and electrochemical probe.     

Lipase-catalyzed enantioselective transesterification of 3-hydroxy-3-(2-thienyl) propanenitrile in liquid carbon dioxide

The transesterification of 3-hydroxy-3-(2-thienyl) propanenitrile catalyzed by Pseudomonas fluorescens lipase (PFL) in liquid carbon dioxide (CO₂) was reported. Compared with that in organic solvent (n-hexane), the catalytic performance of PFL was dramatically enhanced in liquid CO₂. Under the optimal reaction conditions, PFL exhibited an excellent enantioselectivity (E-value: 92.9) with a high enzyme activity (82.5?μmol/g/min). Besides, the remained (S)-3-hydroxy-3-(2-thienyl) propanenitrile with high enantiomeric purity (ee?>?99%) was obtained in 4?h when the conversion was about 52%.

Lipase-catalyzed transesterification of 3-hydroxy-3-(2-thienyl) propanenitrile in liquid CO₂     

Conformational analysis of 12-crown-3 and sodium ion selectivity of electrodes based on bis(12-crown-3) derivatives with malonate spacers

A conformational analysis was performed on two crown ethers (12-crown-3 and 12-crown-4) using a combination of semi-empirical and ab initio methods. The lowest conformations of 12-crown-3 and 12-crown-4 were found to have exodentate C_3v and C₂ structure, respectively. In the case of the sandwich-type complexation, the nucleophilic cavity of 12-crown-3 rather than that of 12-crown-4 seemed to be optimal for complexation with the Na⁺ ion. Four new bis(12-crown-3) derivatives (1–4) were examined as potential sodium ion-selective ionophores in poly(vinylchloride) (PVC) membrane electrodes. The ion-selective electrode (ISE) based on di(1,5,9-trioxacyclododecanylmethyl) 2-dodecyl-2-methylmalonate (1) had the highest selectivity for the sodium ion among the alkali and alkaline earths studied. The sodium ion selectivity of the ISE based on bis(12-crown-3) derivative 1 was superior to that of the ISE based on the bis(12-crown-4) analogue.     

Electrochemically selective determination of dopamine in the presence of ascorbic and uric acids on the surface of the modified Nafion/single wall carbon nanotube/poly(3-methylthiophene) glassy carbon electrodes

A voltammetric method based on a combination of incorporated Nafion, single-walled carbon nanotubes and poly(3-methylthiophene) film-modified glassy carbon electrode (NF/SWCNT/PMT/GCE) has been successfully developed for selective determination of dopamine (DA) in the ternary mixture of dopamine, ascorbic acid (AA) and uric acid (UA) in 0.1M phosphate buffer solution (PBS) pH 4. It was shown that to detect DA from binary DA-AA mixture, the use of NF/PMT/GCE was sufficient, but to detect DA from ternary DA-AA-UA mixture NF/SWCNT/PMT/GCE was required. The later modified electrode exhibits superior electrocatalytic activity towards AA, DA and UA thanks to synergic effect of NF/SWCNT (combining unique properties of SWCNT such as high specific surface area, electrocatalytic and adsorptive properties, with the cation selectivity of NF). On the surface of NF/SWCNT/PMT/GCE AA, DA, UA were oxidized respectively at distinguishable potentials of 0.15, 0.37 and 0.53 V (vs. Ag/AgCl), to form well-defined and sharp peaks, making possible simultaneous determination of each compound. Also, it has several advantages, such as simple preparation method, high sensitivity, low detection limit and excellent reproducibility. Thus, the proposed NF/SWCNT/PMT/GCE could be advantageously employed for the determination of DA in real pharmaceutical formulations.     

Simultaneous determination of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) in food samples using a carbon composite electrode modified with Cu3(PO4)2 immobilized in polyester resin

A simple electrochemical method was developed for the single and simultaneous determination of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) in food samples using square-wave voltammetry (SWV). A carbon composite electrode modified (MCCE) with copper (II) phosphate immobilized in a polyester resin was proposed. The modified electrode allowed the detection of BHA and BHT at potentials lower than those observed at unmodified electrodes. A separation of about 430 mV between the peak oxidation potentials of BHA and BHT in binary mixtures was obtained. The calibration curves for the simultaneous determination of BHA and BHT demonstrated an excellent linear response in the range from 3.4 × 10⁻⁷ to 4.1 × 10⁻⁵ mol L⁻¹ for both compounds. The detection limits for the simultaneous determination of BHA and BHT were 7.2 × 10⁻⁸ and 9.3 × 10⁻⁸ mol L⁻¹, respectively. In addition, the stability and repeatability of the electrode were determined. The proposed method was successfully applied in the simultaneous determination of BHA and BHT in several food samples, and the results obtained were found to be similar to those obtained using the high performance liquid chromatography method with agreement at 95% confidence level.     

玻碳电极上Ru（bpy）3^2＋的吸附及其电致化学发光的研究

通过电化学循环伏安法和电致化学发光方法,研究了Ru(bpy)32 在玻碳电极上的吸附,研究结果表明,2Ru(bpy)3 的浓度和与玻碳材料接触的时间,直接影响了Ru(bpy)32 在玻碳上的吸附.还考察了吸附的Ru(bpy)32 在玻碳电极上被氧化后脱附的情况.     

Bis(3-pyridyl)methylvinylsilane (L1) and 1,2-di(3-quinolyl) dimethyl disilane (L2): Synthesis and complexation reactions. Anion controlled solid state structures of cationic Ag(I)-L1 complex

3-Bromopyridine and 3-bromoquinoline on reaction with n-butyllithium give lithiated products which on reaction with dichloromethylvinylsilane and 1,2-dichlorodimethyldisilane at −78 °C result in the ligands bis(3-pyridyl)methylvinylsilane (L1) and 1,2-di(3-quinolyl)dimethyl disilane (L2). The complexation reactions of both these ligands with Ag(I), Pd(II) and Cu(II) have been explored. The ¹H, ¹³C{¹H} and ²⁹Si{¹H}NMR and IR spectra of both the ligands and their metal complexes have been found characteristic. The complex of L1 with silver(I), [Ag(L1)]ClO₄ (1) gives suitable single crystals characterized by X-ray diffraction. Its structure consists of two dimensional sheets, having 25-membered metallamacrocycle ring, in which Ag has distorted tetrahedral geometry and is bonded to vinyl (η²) group. On reacting AgCF₃SO₃ with L1 and subjecting the single crystals of the resulting complex to X-ray diffraction it has been found that contrary to 1 there is no bond between vinyl group and silver, resulting in infinite molecular strands, in which coordination geometry of silver is distorted trigonal planar. anion acts as a bridge between two molecular strands through F?H (aromatic) and Ag?O secondary interactions. The Ag-C distances in 1 are 2.309(5) and 2.350(12) Å. The CC bond length does not exhibit significant change on bonding with silver in 1.     

槲皮素在聚谷氨酸修饰玻碳电极上的伏安行为及检测

制备了聚谷氨酸修饰玻碳电极,通过循环伏安法和差分脉冲伏安法研究了槲皮素在该修饰电极上的电化学行为。在pH 5.00的B-R缓冲液中,槲皮素在修饰电极上于0.28 V(vs Ag/AgCl)电位处产生一个灵敏的DPV阳极氧化峰,氧化峰电流与槲皮素的浓度在1.0×10-8～5×10-5 mol/L的范围内呈良好的线性关系,最低检测限为4.0×10-9 mol/L。实验表明,聚谷氨酸修饰电极可提高槲皮素的检测灵敏度,该电极用于芦丁水解产物中槲皮素的检测,回收率为103.4%～104.5%。