Titrimetric determination of aluminium in zinc-aluminium alloys, with edta and a cu(II)-selective electrode

The end-point for the titration of EDTA with Cu(II), as measured by a Cu(II)-selective electrode, varies with pH and temperature. Moreover, the effect of pH and temperature on the behaviour of this electrode differs according to whether fluoride is present. As a consequence, the determination of aluminium in zinc-aluminium alloys by the Freegarde and Allen method with use of a Cu(II)-selective electrode must be performed with close control of pH and temperature to maximize accuracy and repeatability.     

固态碳糊电极电位法测定利多卡因注射液

本文报道了一种以利多卡因与单质碘形成的缔合物为电活性物的全固态碳糊利多卡因电极,电极的线性响应范围5.0×10-2～4.0×10-5mol.L-1,级差电位为30mV/pC,检测下限为3.0×10-5mol.L-1。该电极响应迅速,重现性好,用该电极测定了盐酸利多卡因注射液中利多卡因的含量,结果与药典法相符。     

A comparative study of liquid and solid inner contact roxatidine acetate ion-selective electrode membranes

A comparative study was conducted using two designs of a roxatidine acetate (ROX)-selective electrode; a conventional liquid inner contact called electrode A and a graphite-coated solid contact called electrode B. The fabrication of electrodes was based on roxatidine-tetraphenylborate (ROX-TPB) as an ion-association complex in a PVC matrix using different plasticizers. Electrode A has a linear dynamic range of 2.2×10-5 mol/L to 1.0×10-2 mol/L, with a Nernstian slope of 54.7 mV/decade and a detection limit of 1.4×10-6 mol/L. Electrode B shows linearity over the concentration range of 1.0×10-6 mol/L to 1.0×10-2 mol/L, with a Nernstian slope of 51.2 mV/decade and a limit of detection of 1.1×10-7 mol/L which is remarkably improved as a result of diminishing ion fluxes in this solid contact, ion-selective electrode. The proposed sensors display useful analytical characteristics for the determination of ROX in bulk powder and its pharmaceutical formulation. The present electrodes show clear discrimination of ROX from several inorganic, organic ions, sugars, some common drug excipients and the degradation product (3-[3-(1-piperidinyl methyl) phenoxy] propyl amine) of ROX. Furthermore, the proposed electrodes were utilized for the determination of ROX in human plasma, where electrode B covers drug Cmax which indicated its applicability to pharmacokinetic, bioavailability and bioequivalent studies. The results obtained by the proposed electrodes were statistically analyzed and compared with those obtained by a reported HPLC method. No significant difference for either accuracy or precision was observed.     

KTiOPO4单晶膜钾离子选择性电极的研究

本文采用KTiOPO4单晶薄片作为离子活性传感膜, 制备了钾离子选择性电极。20℃时, 其线性响应范围为1.2×10^-^5～1.0mol.dm^-^3氯化钾溶液, 平均响应斜率为58mV/-lgak, 对钠离子的电位选择性系数为4.0×10^-^4。该电极的优点是电极斜率受酸度变化影响小, 稳定性和重现性好, 寿命长。     

Weighted calibration with reduced number of signals by weighing factor modelling: Application to the identification of explosives by ion chromatography

The linear weighted regression model (LW) can be used to calibrate analytical instrumentation in a range of quantities (e.g. concentration or mass) wider than possible by the linear unweighted regression model, LuW (i.e. the least squares regression model), since this model can be applied when signals are not equally precise through the calibration range. If precision of signals varies within the calibration range, the regression line should be defined taking into account that more precise signals are more reliable and should count more to define regression parameters. Nevertheless, the LW requires the determination of the variation of signals precision through the calibration range. Typically, this information is collected experimentally for each calibration, requiring a large number of replicate collection of signals of calibrators. This work proposes reducing the number of signals needed to perform LW calibrations by developing models of weighing factors robust to daily variations of instrument sensibility. These models were applied to the determination of the ionic composition of the water soluble fraction of explosives. The adequacy of the developed models was tested through the analysis of control standards, certified reference materials and the ion balance of anions and cations in aqueous extracts of explosives, considering the measurement uncertainty estimated by detailed metrological models. The high success rate of the comparisons between estimated and known quantity values of reference solutions, considering results uncertainty, proves the validity of developed metrological models. The relative expanded measurement uncertainty of single determinations ranged from 1.93% to 35.7% for calibrations performed along 4 months.     

Coated-wire ion-selective electrode for the determination of gold(III)

A coated-wire gold(III)-selective electrode based on the 1,2,4,6-tetraphenyl-pyridinium tetrachloroaurate(III) ion-pair is described. The response is Nernstian in the gold concentration range 10^?2–3 × 10^?6 (slope 59.0 mV/pAu). Of the 22 ions tested, only the interference of thallium(III) is important. The electrode is applied to the determination of gold in an Ag-Pd-Au alloy with satisfactory results.     

A highly selective and sensitive thorium(IV) PVC membrane electrode based on a dithio-tetraaza macrocyclic compound.

A poly(vinyl chloride)-based membrane composed of dithio-tetraaza macrocyclic compound as a neutral carrier with sodium tetraphenylborate (NaTPB) as an anion excluder and nitrobenzene (NB) as plasticizer was prepared and investigated as a Th(IV)-selective electrode. The electrode exhibits a Nernstian slope of 14.2 +/- 0.3 mV per decade over a wide concentration range (1.0 x 10(-6) to 1.0 x 10(-1) M) with a detection limit of 8.0 x 10(-7) M between pH 3.5 and 9.5. The response time of the sensor is about 10 s and it can be used over a period of 5 months without any divergence in potential. The proposed membrane sensor revealed a good selectivity for Th(IV) over a wide variety of other metal ions and proved to be a better electrode in many respects than those reported in the literature. It was successfully applied as an electrode indicator as well as in the direct determination of thorium ions in standard and real samples.     

Construction of a new Hg(2+)-selective liquid-state electrode

The construction and basic characteristics of a new liquid-state Hg(2+)-selective membrane electrode are discussed. The membrane consists of the PAN chelate of Hg(II), dissolved in CHCl(3). The linear response range of the electrode is 10(-1) -10(-5)M Hg(2+) with a slope of 28.5 mV/decade of concentration. The response time of the electrode in dilute solutions is less than 3 min, and in concentrated solutions it is only a few sec. The electrode has been used in precipitation or complexation titrations in which Hg(2+) is involved (e.g., in the determination of some organic compounds in drug synthesis).     

A solid state Cr(VI) ion-selective electrode based on polypyrrole

We report on a graphite electrode onto which polypyrrole was electrodeposited and then doped with chromate ion. This electrode can serve as a Cr(VI)-selective solid-state electrode. Electropolymerization of pyrrole was performed potentiostatically at 0.80?V (vs. SCE) using battery graphite as the working electrode in a solution containing 0.10?M of pyrrole and 20?mM of chromate. A platinum wire was used as an auxiliary electrode. The new electrode displays high selectivity, a very wide dynamic range, a sufficiently fast response time and a good shelf lifetime. It shows a linear Nernstian response over 1.0?×?10^?6 to 1.0?×?10^?1?M concentration range (with a slope of 26.55?±?0.20?mV per log of concentration). The detection limit is 0.5?μM, and the pH optimum is 7.0.

An integrated electrochemical fructose biosensor based on tetrathiafulvalene-modified self-assembled monolayers on gold electrodes

An integrated amperometric fructose biosensor based on a gold electrode (AuE) modified with a self-assembled monolayer (SAM) of 3-mercaptopropionic acid (MPA) on which fructose dehydrogenase (FDH) and the mediator tetrathiafulvalene (TTF) are co-immobilized by cross-linking with glutaraldehyde is reported. Variables concerning the behavior of the biosensor were optimized by taking the slope value obtained for the fructose calibration plot in the 0.1–1.0 mM concentration range as a criterion of selection. At an applied potential of +0.20 V, a good repeatability of such slope values (RSD=6.7%, n=10) was obtained with no need to apply a cleaning or pretreatment procedure to the modified electrode. Moreover, results from five different TTF-FDH-MPA-AuEs yielded a RSD of 5.8%. The useful lifetime of one single biosensor was approximately 30 days, exhibiting a 93% of the original response on the 33rd day. A linear calibration graph was obtained for fructose over the 1.0×10^–5–1.0×10^–3 M range, with a limit of detection of 2.4×10^–6 M. The effect of potential interferents was evaluated. The TTF-FDH-MPA-AuE also performed well in the flow-injection mode. The biosensor was used for the determination of fructose in real samples, and the results compared with those provided by using a commercial enzyme test kit.     

Uncertainties in Determination of pH

 A statistical analysis of multi-point calibration procedure for practical measurement of pH under laboratory conditions is given. The procedure is shown to provide the necessary elements for simple assignment of an uncertainty to a pH measurement – an essential element of quality control. Performance of ordinary least squares regression for prediction of confidence limits is compared to orthogonal regression, inverse regression and Monte Carlo simulations. In case of pH measurement by multi-point calibration procedure, methods considering uncertainties in both axes are found to be statistically more satisfactory than ordinary least squares regression. By analysis of 50 pH calibration data, randomly selected from 250 5-point glass electrode calibrations, it is found that the practical differences, however, are of minor importance. The significance of uncertainty in pH is demonstrated for an example from metal ion speciation in aqueous solution. Received September 20, 1999. Revision April 19, 2000.     

Voltammetric Determination of Methimazole Using a Carbon Paste Electrode Modified with a Schiff Base Complex of Cobalt

The electrochemical behavior of methimazole, as an antithyroid agent, is investigated on the surface of a carbon‐paste electrode modified with a newly synthesized Schiff base complex of cobalt. The prepared modified electrode showed an efficient catalytic role in the electrochemical oxidation of methimazole, leading to remarkable decrease in oxidation overpotential and enhancement of the kinetics of the electrode reaction. The mechanism of the electrocatalytic process on the surface of the modified electrode is analyzed by obtaining the cyclic voltammograms in various potential sweep rates and pHs of the buffer solutions. The differential pulse voltammetry is applied as a very sensitive analytical method for the determination of sub‐micromolar amounts of methimazole. A linear dynamic range of 1×10^?6 to 1×10^?4 M with a detection limit of 5×10^?7 M is resulted for methimazole. The modified electrode is successfully applied for the accurate determination of methimazole in pharmaceutical and clinical preparations. The linear range in calibration curves remains constant in addition to tablet preparations of methimazole and also in spiking to the synthetic human serum samples. In comparison to calibration curves in background buffer solution, the slope of the curves showed a variation less than 3% in determinations in background solutions of tablet and human synthetic serum samples. These results showed high efficiency of the Voltammetric procedure for accurate determination of methimazole in drug and clinical preparations. The modified electrode can be prepared very easy and renewed in its surface by simple polishing. The reproducibility of the electrode response, based on ten measurements during two month, was 3.2% for the slope of the calibration curve.     

Schiff碱型和仲胺型双冠醚II: 用双冠醚作载体的PVC膜钾离子选择性电极

用六个含二个苯并-15-冠-5单元的席夫碱型和仲胺型新型双冠醚作载体制备了钾离子选择性PVC膜电极,并研究了它们的电极行为,这些电极对所有的其它碱金属和碱土金属离子展现出显著的钾离子选择性,可期望有一定的应用价值.     

Anodic stripping voltammetry of silver(I) using a carbon paste electrode modified with multi-walled carbon nanotubes

We describe a silver(I)-selective carbon paste electrode modified with multi-walled carbon nanotubes and a silver-chelating Schiff base, and its electrochemical response to Ag(I). Effects of reduction potential and time, accumulation time, pH of the solution and the stripping medium were studied by differential pulse anodic stripping voltammetry and optimized. The findings resulted in a method for the determination of silver over a linear response range (from 0.5 to 235 ng?mL^?1) and with a detection limit as low as 0.08 ng?mL^?1. The sensor displays good repeatability (with the RSD of ±?2.75 % for 7 replicates) and was applied to the determination of Ag(I) in water samples and X-ray photographic films.

Electroanalytical Determination of Vancomycin at a Graphene‐modified Electrode: Comparison of Electrochemical Property between Graphene,Carbon Nanotube,and Carbon Black

Carbon nanotube, graphene and carbon black, as electrode modifiers, were compared and evaluated for the electrochemical determination of vancomycin. Among them, the best results were obtained at the graphene‐modified electrode. Additions of vancomycin using square wave voltammetry at the graphene‐modified electrode showed a linear range from 0.70 μM to 50 μM and a detection limit of 0.20 μM was obtained. To control the correct dose of vancomycin and reduce its side effects, its accurate determination in blood plasma is very important. Therefore, the method was applied for the vancomycin determination in spiked human plasma samples and satisfactory recoveries were observed. The developed method exhibited fast analysis, high sensitivity, good repeatability and freedom from other interfering species.     

Voltammetric Determination of Chloride Ion in Automotive Fuel Ethanol

Cathodic stripping voltammetry with a hanging mercury drop electrode was used in this study to determine chloride ions in automotive fuel ethanol. Choosing the correct stripping voltammetric technique, the correct choice of deposition potential and time provided well defined voltammetric waves with good repeatability and relatively small errors, with a determination limit of 0.13 mg L^?1, for only 10 s of deposition time, with better sensitivity and repeatability than the normalized method, as well as consumed less volume of the sample, being suitable for routine analysis.     

Organic analysis with a new Ag(+)-selective membrane electrode

A new Ag(+)-selective membrane electrode obtained by impregnating a graphite rod (attached to the end of a Teflon tube) with the silver(I) chelate of 1-(2',3',5'-tri-O-benzoyl-beta-D-ribofuranosyl)-4-thioxo-5-methylthio-6-azauracil dissolved in chloroform gives a stable and reproducible response to silver in the 10(-1)-10(-5)M range with a slope of 60 mV/decade. A new method for determination of some beta-chlorovinyl ketones is based on use of the electrode in potentiometric titration of the chloride displaced by tertiary amines from beta-chlorovinyl ketones in forming the corresponding quaternary ammonium salts.     

2011年约稿： 电感耦合等离子体原子发射光谱法测定铜合金中锆量的不确定度评定

讨论了采用电感耦合等离子体发射光谱法测定铜合金中锆量分析结果不确定度产生的原因。建立了数学模型,对测量重复性,标准溶液,标准曲线变动性,试液体积,试样称量,数字修约等引起的不确定分量进行评定,计算了合成标准不确定度和扩展不确定度,并给出铜合金中锆量测定结果的报告。评定结果表明：测量重复性,标准曲线线性回归引起的不确定度对总不确定度影响最大。所以,在测定中应进行多次平行测定,特别注意标准曲线的校正和绘制校准曲线所用标准样品的选择。     

Chromium(III) ion selective electrode based on glyoxal bis(2-hydroxyanil)

A poly(vinyl chloride) membrane based on glyoxal bis(2-hydroxyanil) as membrane carrier was prepared and investigated as a Cr(III)-selective electrode. The electrode has a linear dynamic range of 3.0×10⁻⁶-1.0×10⁻² mol l⁻¹, with a Nernstian slope of 19.8±0.5 mV per decade and a detection limit of 6.3×10⁻⁷ mol l⁻¹. It has a fast response time of <20 s and can be used for at least 3 months without any considerable divergence in potential. The proposed electrode revealed good sensitivities for Cr(III) over a wide variety of metal ions and could be used in a pH range of 2.7-6.5. Above all, the membrane sensor has been used very successfully for the analysis of some food materials and alloys for the determination of Cr(III) ion.     

Fabrication of Nano Flower‐shaped Platinum on Glassy Carbon Electrode as a Sensitive Sensor for Lead Electrochemical Analysis

Platinum nanoflowers modified glassy carbon electrodes (PtNFs/GCE) was fabricated simply for lead determination in water samples. The modified electrodes were prepared by electrodeposition in hexachloroplatinic acid solution at constant potential. The influence of deposition time and potential on surface morphology, chemical composition, electrochemical properties of electrode were investigated. At ?0.2 V of potential and 150 s of deposition duration, platinum developed as nanoflower shape and scattered densely all over the glassy carbon surface, producing the largest electrochemically active surface areas. The highest differential pulse stripping voltammetry (DPSV) signal of lead was obtained by using the prepared electrode. Under optimized experimental condition of electrolyte, accumulation potential and time, the peak current was found to be linear proportion to lead concentration in range of 1 to 100 μg L^?1 (slope=0.371) with a limit of detection of 0.398 μg L^?1. The method has good repeatability and reproducibility with relative standard deviations of 1.47 % and 4.83 %, respectively. The modified PtNFs/GCE also demonstrated an excellent long‐term stability with only 9 % decrease in Pb peak current over 30 days. Moreover, the performance of the modified PtNFs/GCE in determination of Pb(II) in two industrial wastewaters was good agreement with data obtained by a graphite furnace atomic absorption spectrometry (GFAAS) method.