氯离子伏安刻蚀制备高活性多孔银膜及其对三氯乙酸的电化学检测（英文）

采用无机阴离子促进的伏安刻蚀技术在银线表面制备高活性多孔银膜。优选的氯离子在伏安条件下通过微反应刻蚀,促使银丝表面形成自支撑的多孔通道。当在银丝电极上施加连续的正电位后,银电极表面在氯离子作用下快速形成AgCl膜,经施加的电位反向,在电化学还原作用下氯离子剥离,AgCl膜自发转化为自支撑的多孔银膜。研究表明,制备的多孔银膜(p-Ag film)对三氯乙酸具有较高的电催化活性,与原始银丝(r-Ag wire)相比,电化学活性表面积和电催化性能分别提高了174和3.7倍。将其用于三氯乙酸的电化学检测时,在浓度为0.1~518.1μmol·L-1范围内,制备的多孔银膜电极的最低检测限可达70 nmol·L-1(拟合相关性系数R2=0.9983)。     

Flow injection potentiometric detection of trimethylamine in seafood using tungsten oxide electrode

A simple flow injection gas/diffusion method for the determination of trimethylamine (TMA) in seafood with potentiometric detection using tungsten oxide electrode has been developed. The method is based on the diffusion of TMA through a PTFE membrane from a sodium hydroxide donor stream to a phosphate buffer acceptor stream. The TMA in the acceptor stream passes through an electrochemical flow cell containing a tungsten oxide wire and a silver/silver chloride electrode, where TMA was sensitively detected. The parameters affecting the sensitivity of the electrode such as sodium hydroxide concentration, buffer concentration, pH, flow rate and injected volume were studied in details. The electrode response was linear in the concentration range from 1 to 10 μg ml⁻¹ TMA with a correlation coefficient (R²) of 0.991 and a detection limit of 0.05 μg ml⁻¹ TMA. The intra- and inter-days precision (R.S.D.) was found to be, respectively, 1.20 and 1.6% (n=6). The method was applied to the determination of TMA in fish tissue and recoveries of 99-100% were obtained for fish extracts. Results were in close agreement with those obtained by the existing classical official method. Common interference from those species that can diffuse through the membrane were removed by the addition of formaldehyde to the seafood extract. The method is simple, feasible with satisfactory accuracy and precision and thus, could be used for monitoring seafood quality with a sampling rate of 20±2 sample h⁻¹.     

Silver particle-decorated carbon paste electrode based on ionic liquid for improved determination of nitrite

A simple silver particle-modified carbon paste electrode is proposed for the determination of low concentration levels of nitrite ions. The electrode consists of a carbon powder decorated with silver sub-micrometre particles (AgPs) and a hydrophobic ionic liquid trihexyltetradecylphosphonium chloride as a binder. It has been shown that AgPs exhibit a strong electrocatalytic effect on the nitrite oxidation. For optimal electroanalytical performance the electrode was conditioned via silver oxidation/reduction cycle. The electrode revealed a linear square-wave voltammetric response in a wide examined concentration range of 0.05 to 1.0 mmol L^− 1, limit of detection (LOD) of 3 μmol L^− 1 and excellent repeatability with RSD of 0.3%.     

Development of sequential injection-lab-at-valve (SI-LAV) micro-extraction instrumentation for the spectrophotometric determination of an anionic surfactant.

The development of instrumentation for sequential injection analysis with a "lab-at-valve" (SIA-LAV) micro-extraction system is presented. The extractive determination of an anionic surfactant using methylene blue was selected as a model. Sample, reagents and organic solvent were sequentially aspirated into an extraction coil connected to the center of a selection valve, where extraction took place by flow reversal. The aqueous and organic phases were separated in a LAV unit attached to one port of the valve. The LAV unit situated a fiber-optic spectrophotometer to monitor the absorbance change of the extract product in the organic phase. The developed SIA-LAV system offers an alternative micro-total analysis system for automated micro-extraction.     

Determination of total chlorine in waste oil

Summary A simple method has been developed to determine the concentration of organic chlorine in waste oil. The determination is based on the conversion of organic chlorine to inorganic chloride by reaction with sodium biphenyl followed by extraction with nitric acid and a mixture of nitric acid and water. The concentration of chloride is determined by direct potentiometry with an ion-selective electrode. The limit of determination amounts to 3·10^–5 mol·l^–1 chloride ions with a standard deviation of 3.5%. Different samples of waste oil have been analyzed and the results have been compared to those obtained by combustion in a H₂/O₂ flame followed by potentiometric titration with silver nitrate.     

Gas diffusion-flow injection determination of total inorganic carbon in water using tungsten oxide electrode

A novel gas diffusion-flow injection method has been developed for the rapid and sensitive determination of total inorganic carbon (TIC) in water. The method is based on the diffusion of CO₂ across gas permeable membrane from a donor stream containing 0.1 M HCl to an acceptor stream of sodium acetate (10⁻⁵ mol l⁻¹ and pH 10). The CO₂ trapped in the acceptor stream passes through an electrochemical flow cell contains a tungsten oxide wire and a silver/silver chloride electrode, where it was sensitively detected. The parameters affecting the sensitivity of the electrode such as buffer concentration, pH, flow rate and injected volume were studied in detail. The electrode response was linear in the concentration range from 5 to 100 μg ml⁻¹ CO₃²⁻ with a correlation coefficient (R²) of 0.998. Precision (R.S.D.) was 1.42% for 20 μg ml⁻¹ standard solution of CO₃²⁻ (n=10). The detection limit was 0.20 μg ml⁻¹ CO₃²⁻. The method was evaluated by the injection of real natural water samples and an average recovery of 100.1% was obtained. The sampling rate was 30 samples h⁻¹. The method is simple, feasible with satisfactory accuracy and precision and thus could be used for monitoring TIC in water.     

Determination of chloride in admixtures and aggregates for cement by a simple flow injection potentiometric system

A simple flow injection system using three 3-way solenoid valves as an electric control injection valve and with a simple home-made chloride ion selective electrode based on Ag/AgCl wire as a sensor for determination of water soluble chloride in admixtures and aggregates for cement has been developed. A liquid sample or an extract was injected into a water carrier stream which was then merged with 0.1M KNO(3) stream and flowed through a flow cell where the solution will be in contact with the sensor, producing a potential change recorded as a peak. A calibration graph in range of 10-100 mg L(-1) was obtained with a detection limit of 2 mg L(-1). Relative standard deviations for 7 replicates injecting of 20, 60 and 90 mg L(-1) chloride solutions were 1.0, 1.2 and 0.6%, respectively. Sample throughput of 60 h(-1) was achieved with the consumption of 1 mL each of electrolyte solution and water carrier. The developed method was validated by the British Standard methods.     

Determination of Low Cyanide Levels Using a Deposited-on-Wire Silver/Silver Selenide Electrode

Because of extreme toxicity, cyanide is important in water quality control,and cyanide-selective electrode method is one of the best methods for fast determination of cyanide content. In this paper, a silver/silver selenide electrode is prepared quickly by holding a silver wire in vapours of molten selenide. The electrodes were tested in following steps.     

Needle-type ultra micro silver/silver chloride reference electrode for use in micro-electrochemistry.

A needle-type ultra micro silver/silver chloride reference electrode having a micro capillary with outer and inner diameters of 1.0 microm and 0.5 +/- 0.2 microm, respectively, was constructed. This micro reference electrode can be stuck into a living cell, and is applicable to use in very small environments, such as an electrochemical cell of an electrochemical scanning tunneling microscope or the detection portion of a micro-TAS. Excellent stability and repeatability of the micro reference electrode potential could be obtained by filling the micro capillary with agar gel containing 3.33 mol/L potassium chloride as a salt bridge, by covering the bare part of the silver wire on which silver chloride was deposited, and by electromagnetic shielding of the measurement cell and wire lead from the electromagnetic waves. The electrode showed stable potential for 7 days after its fabrication using 3.3 mol/L potassium chloride aqueous solution containing silver chloride as an internal electrolyte solution. The electrode exhibited constant electrode potential and excellent stability in test solutions of pH 5-9. The electrode potential of a commercial pH glass electrode measured against the micro reference electrode in standard pH buffer solutions was in good accordance with the Nernst equation.     

A Cryptate Reference Electrode for Ionic Liquids

The cryptate electrode (Ag/Ag⁺222), prepared by immersing silver wire in a solution of silver(I) salt and the cryptand 222 (4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane) in ionic liquids have been studied. The potential of the electrode is stabilized by the equilibrium of the Ag⁺ ion complexation by the cryptand, similarly to the potential stabilization by the ionic product of slightly soluble salts, used in aqueous electrodes of the second kind. The Ag/Ag⁺222 cryptate electrode (concentration of the cryptate was much higher than the silver(I) cation concentration, [222]>[Ag⁺]) may be used as a reference electrode in room temperature ionic liquids. The potential of the Ag/Ag⁺222 electrode is less sensitive to the presence of impurities, such as halides or water, in comparison to the Ag/Ag⁺ electrode. After anodic or cathodic polarization, the potential of the Ag/Ag⁺222 electrode comes back to the initial open circuit potential quickly. Preparation of the Ag/Ag⁺222 reference electrode is very easy: a silver wire is immersed in a solution of Ag⁺ salt and cryptand 222 (both available commercially) in the ionic liquid under study.     

Exploiting sequential injection analysis with lab-at-valve (LAV) approach for on-line liquid-liquid micro-extraction spectrophotometry

Sequential injection analysis (SIA) with lab-at-valve (LAV) approach for on-line liquid-liquid micro-extraction has been exploited. Sample, reagent and organic solvent were sequentially aspirated into a coil attached to a central port of a conventional multiposition selection valve, where the extraction process was performed. The aqueous and organic phases were separated in a conical separating chamber LAV unit attached at one port of the valve. The organic phase containing extracted product was then monitored spectrophotometrically. The system offers a novel alternative on-line automated extraction in a micro-scale and has been successfully demonstrated for the assays of diphenhydramine hydrochloride (DPHH) in pharmaceutical preparations and anionic surfactant in water samples.     

No more conventional reference electrode: Transition time for determining chloride ion concentration

Ion selective electrodes (ISE) are used extensively for the potentiometric determination of ion concentrations in electrolytes. However, the inherent drift in these measurements and the requirement of a stable reference electrode restrict the feasibility of this method for long-term in-situ applications. This work presents a chronopotentiometric approach to minimize drift and avoid the use of a conventional reference electrode for measuring chloride ion concentration. An anodic current pulse is applied to a Ag/AgCl working electrode which initiates a faradaic reaction that depletes the chloride ions near the electrode surface. The rate of change in potential at the Ag/AgCl electrode, due to chloride ion depletion, reaches an inflection point once the chloride ions deplete completely near the electrode surface. The moment of the inflection point, also known as the transition time, is a function of the chloride ion concentration and is described by the Sand equation. It is shown that the square root of the transition time is linearly proportional to the chloride ion concentration. Drift in the response over two weeks is negligible: 59 μM/day when measuring 1 mM of Cl⁻ ions using a 10 A m⁻² current pulse. The transition time at a specific ion concentration can be tuned by the applied current pulse, e.g., in a solution containing 5 mM chloride ions, the transition times with current pulses of 10 and 20 A m⁻² are 1.56 and 0.25 s, respectively. The moment of inflection determines the response, and thus is independent of the absolute potential of reference electrode. Therefore, any metal wire can act as a pseudo-reference electrode, enabling this approach for long-term and integrated-sensor applications such as measurement inside concrete structures.     

Synthesis of silver nanowires and their applications in the electrochemical detection of halide

A silver nanowires modified platinum (Ag NWs/Pt) electrode was developed for simultaneous and selective determination of chloride, bromide and iodide ions by cyclic voltammetry in aqueous solutions. Silver nanowires were synthesized by an l-cysteine-assisted poly (vinyl pyrrolidone) (PVP)-mediated polyol route. X-ray diffraction (XRD) and scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) were employed to investigate the prepared nanowires. The intrinsic high surface area and the fast electron transfer rate ascribed from the nanowire structure could further improve halide detection performance. The determination was based on measurement of the well-separated oxidation peak currents of respective silver halides formed on the surface of silver during an anodic potential sweep. The concentration range was linear from 50 μM to 20.2 mM for bromide and iodide and 200 μM to 20.2 mM for chloride, and the sensitivity was 0.059 μA/mM, 0.042 μA/mM and 0.032 μA/mM for chloride, bromide and iodide, respectively. The correlation coefficient was 0.999 in each case. The Ag NWs/Pt electrode offered a useful platform for the development of a highly sensitive halide sensor.     

Potentiometric detection of halides and pseudohalides in anion chromatography

A small piece of silver wire, coated with an insoluble silver salt, can be used as a selective potentiometric detector for halides in ion chromatography. Several coated electrodes were examined by electron microscopy and their response to various anions evaluated in a flow-injection system. A silver/silver chloride was found to be a selective and reproducible detector for chloride, bromide, iodide, thiocyanate and thiosulfate separated by ion chromatography. Calibration curves were non-linear and had slopes ranging from 40 to 60 mV per concentration decade in the range 0.1–2 mM. A working range of 0.05–2 mM was used. This electrode is also satisfactory when gradient elution is used in ion chromatography.     

Discontinuous-flow potentiometric determination of chloride in a large-volume wall-jet cell using an ion-selective electrode based on a silver chloride film chemically deposited on a silver iodide support

A robust and sensitive chloride ion-selective electrode can be prepared by modifying the surface of an iodide-selective electrode using the chemical reaction with mercuric chloride in an oxidizing medium containing excess chloride. A thin film of silver chloride is thus formed ensuring a rapid and reproducible response to chloride. The analytical parameters of this electrode are similar to those of commercial silver chloride ion-selective electrodes, but its electrical impedance and signal noise are substantially lower and the response somewhat faster. Its sensitivity toward surfactants is somewhat suppressed. The electrode was used for discontinuous flow potentiometric (DFP) determinations in a large-volume wall-jet cell in which the electrode surface can be continuously reactivated by a cleaning solution contained in the cell. The method was applied to determination of chloride in ground waters from an industrial waste dumping site. The limit of determination is low 9 mug Cl(-)/l (2.6 x 10(-7)M), the precision good (the relative standard deviation varies from 0.6 to 3.0% for chloride contents from 2.90 to 0.15 mg/l, respectively) and the method correlates satisfactorily with the results of an indirect AAS determination of chloride. The sample throughput is high-90 measurements can be carried out per hour, corresponding to 30-40 determinations per hour.     

基于三维纳米银修饰电极的硝酸根微型传感芯片研究

研制一种基于金叉指微电极阵列(IDA)的电流型硝酸根离子(NO-3)微传感电极芯片.基于微机电系统(Micro-Electro-Mechanical Systems,MEMS)工艺制备金IDA微电极,通过电化学沉积技术在IDA微电极表面修饰三维枝状结构纳米银敏感膜,利用敏感膜对硝酸根离子良好的电催化还原性能,采用脉冲方波伏安(SWV)电化学测量方法,实现对硝酸根离子在25～1000μmol/L浓度范围内的快速检测,灵敏度达9.5 nA/(μmol/L),线性度为99.98%,检测下限为10μmol/L.考察水体中常见的NO-2,F-,3PO 4-,SO 42-,2CO3-,NH+4,Na+和K+等离子对该传感芯片的干扰性能,传感芯片表现出较好的抗干扰性能.制备的三维枝状结构纳米银修饰IDA微电极可实现水环境(pH 5.0～9.0)中NO-3的电化学检测,对应用于自然水环境中硝酸根离子的现场检测具有积极意义.     

Development of a system with enzyme reactors for the determination of fish freshness

A continuous system for the determination of fish freshness with double enzyme reactors was developed and applied to the determination of the freshness indicator K [Formula: see text] where IMP, HxR and Hx are Inosine monophosphate, Inosine and Hypoxanthine, respectively. The system was assembled with a three electrode screen-printed element (graphite as working electrode, silver as counter and silver, silver chloride as reference electrode) placed in a flow cell, a sample injection valve and two enzyme reactors. The determination of the total amount of HxR and Hx is realized by flowing the sample through two reactors in series: one reactor was packed with nucleoside phosphorylase (Np) and the other with xanthine oxidase (XO) immobilized on aminopropyl glass. Similarly, the other term of the equation was evaluated by flowing through the two reactors the sample treated by Alkaline phosphatase (AlP) for 5-10 min at 45 degrees C. One assay could be completed within 5 min. The system for the determination of fish freshness was reproducible within 2-3% (n=4). The immobilized enzymes were fairly stable for at least 3 months at 4 degrees C. More than 200-300 samples could be analyzed in about one month by using these enzyme reactors provided the disposable screen-printed electrode should be changed every 30-40 real samples. The results obtained suggest that the proposed sensor system provides a simple, rapid and economical method for the determination of fish freshness (K). We applied the present system with two reactors for the determination of K values in fish samples and compared the results with those obtained by the XO-reactor. Correlation factor and regression line between the two methods were 0.992 and Y=-3.14+1.03X respectively. We concluded that the present flow injection analysis (FIA) system with XO and Np reactors was suitable as a simple, easy to handle and reliable instrument for quality control in the fish industry.     

FIA-potentiometry in the sub-Nernstian response region for rapid and direct chloride assays in milk and in coconut water

A simple and reliable FIA-potentiometric system for rapid assays of chloride in certain food samples is described and evaluated. The system is constituted by an aquarium air pump to propel the carrier solution, a manually operated injector, a homemade dialysis flow cell, a solid-state chloride detector (Ag/AgCl), a reference electrode and a multimeter connected to a microcomputer for data acquisition. The dialysis unit enables direct analysis of liquid food samples without any other previous treatment. The principal novelties are the precision (R.S.D. of 1.2% for whole milk) and rapidity (90 determinations/h) of FIA measurements near and below the lower end of the linear (Nernstian) response region of the chloride ion-selective electrode (ISE), with an estimated detection limit (3 s) of 0.4 mg L⁻¹ Cl⁻ in the sample injected in donor stream. Data of peak potential versus sample chloride concentration (donor stream) was accurately fitted with a quadratic polynomial over the range between 4 and 1000 mg L⁻¹ (r² = 0.9999) and used as a calibration curve. The method was applied to the determination of chloride in milk and in coconut water samples. The validation of the results was done by comparison with a NIST reference material (milk) or by capillary electrophoresis (coconut water). For all analysis, no significant difference at a 95% confidence level was observed.     

The renovated silver ring electrode in determination of lead traces by differential pulse anodic stripping voltammetry

The study of a new type of working electrode - the renovated silver ring electrode (RSRE) - for lead ions detection via differential pulse anodic stripping voltammetry (DP ASV) without removal of oxygen is reported. The only four constituents of the RSRE: a specially constructed silver ring electrode, a silver sheet used as silver counter/quasi-reference electrode and a silicon O-ring, are fastened together in a polypropylene body. The renovation of this electrode is carried out through mechanical removal of solid contaminants and electrochemical activation in the electrolyte which fills the RSRE body. Excellent repeatability and reproducibility - also in organic samples solutions - were reached in a period of a few weeks through the renovation of the electrode surface before each measurement. The reduction and stripping of lead on silver electrode under the DP ASV conditions are underpotential deposition/dissolution phenomena. The RSRE is used for the determination of Pb ions in concentrations ranging from 1 × 10⁻⁹ to 1 × 10⁻⁷ M. The repeatability of DP ASV runs in synthetic solutions covering the entire concentration range is better than 2%. Obtained calibration curves are represented by a correlation coefficient of at least 0.999. The detection limit (LOD) for the time of electrodeposition equal to 60 s is 0.2 × 10⁻⁹ M. LOD for Pb²⁺ detection at the RSRE is similar to this reported for a rotating silver electrode in subtractive anodic stripping voltammetry (E. Kirowa-Eisner, et al., Anal. Chim. Acta, 385 (1999) 325). The analysis of Pb²⁺ in synthetic solutions with and without surfactants, certified reference materials and natural water samples have been performed.     

Flow injection potentiometric determination of saccharin in dietary products with relocation of filtration unit

A flow injection potentiometric procedure for saccharin determination in dietary products is proposed. Saccharin is precipitated as mercurous saccharinate and the excess of the mercurous cation is potentiometrically measured using a silver wire coated with a mercury film as the working electrode. A filter unit is used to avoid contact between the precipitate and the electrode surface. With relocation in the flow manifold, the accumulated precipitate is removed on-line. Sucrose, glucose, aspartame, sodium cyclamate and sodium benzoate do not interfere when present in amounts similar to those observed in commercial products. Results are comparable with those obtained by UV-spectrophotometry and the correlation coefficient between methods is equal to 0.9930. A linear relationship between DeltaE (mV) and the logarithm of saccharin concentration was obtained in the saccharin concentration range 2 x 10(-3) - 1 x 10(-2)M. The sampling frequency is 60/hour and only 0.76 mg of Hg(2+)(2) is consumed in each determination.