Theory of the surface acoustic wave/impedance sensor system and its application to the end-point determination in titrimetry

Theory and characteristics of the surface acoustic wave (SAW)/impedance sensor system in electrolyte solution are reported. This kind of sensor was constructed by a 62-MHz SAW resonator and a pair of conductive electrodes in series. By using the circuit network analysis theory, two oscillation equations were derived and used to explain the frequency-shift response to solution conductance. Results showed that the sensor possesses high sensitivity to the solution conductivity and can be applied to conductivity measurements in solution. Its sensitivity and accuracy could be improved in the presence of a large amount of unreacting foreign electrolytes. The sensor was successfully applied to four types of titration (acid-base, precipitation, oxidation-reduction and compleximetric titration) by monitoring the frequency-shift response. Factors influencing the frequencimetric titration curve were also investigated. Analytes at levels down to 1 × 10⁻⁵ M could be determined by the proposed titration technique. The total acidity in several food samples was determined and the results were consistent with those obtained by conventional methods.     

The extended Langmuir's method and its application to double-layer interaction

On the basis of Langmuir's suggestion we simplified Poisson-Boltzmann equation and derived the relation of surface potential, potential midway and the plate distance. Thus we used the force equation derived by Langmuir to calculate the interaction energy. This method may apply to the cases of high potential, low potential, constant potential, and constant charge.     

Investigation of the use of thermometric titrimetry for the determination of acidic substances in wine

The use of thermometric titrimetry in the determination of acidic substances in red wine is described. The titration curve obtained in the thermometric titration of red wine with strong base presents two inflections. The stoichiometry corresponding to the first inflection presents good agreement with the so-called "total acidity" of wine, and is proposed for its determination. The second inflection is related to the content of phenolic substances in red wine.     

Exploration of the electrical double-layer structure: Influence of electrolyte components on the double-layer capacitance and potential of maximum entropy

Understanding the electrical double-layer structure is of paramount importance for designing efficient electrochemical energy conversion systems. Under this aspect, this short review explores the influence of the electrolyte on parameters such as the double-layer capacitance and the potential of maximum entropy. Investigation of those parameters offers a deeper understanding on how the interfacial structure changes near reaction conditions. As a consequence, one can tune the catalyst activity by creating a more favorable environment in the electrolyte. The aim of this short review is to provide the reader with recent studies examining the electrode/electrolyte interface from experimental and theoretical standpoints.     

The use of sulfamic acid as a primary standard in nonaqueous titrimetry

A method has been developed for the standardization of a typical nonaqueous base lithium methoxide, with an inorganic primary standard, sulfamic acid. 'T'his acid was found to dissolve readily in four independant basic solvents, dimethyl formamide, ethylenediamine, n-butylamine and dimethyl sulfoxide. Sulfamic acid could be titrated in each of these solvents, by both visual and potentiometric means with lithium methoxide dissolved in benzene-methanol. No gels nor precipitates resulted in the course of the titrations and the accuracy of the method was comparable to that obtained using benzoic acid as the primary standard. Conductometric titrations were also performed using sulfamic acid dissolved in two systems, dimethyl formamide and glacial acetic acid. In the latter solvent it was possible to titrate sulfamic acid with perchloric acid in glacial acetic acid.     

Modeling the surface phenomena in carbon paste electrodes by low frequency impedance and double-layer capacitance measurements

Impedance and capacitance studies have been performed with covalently coupled Glucose oxidase (GOD) enzyme, covalently coupled flavin adenine dinucleotide (FAD), reconstituted GOD enzyme and blank carbon paste electrodes to study the changes in the electrochemical interfacial properties. Impedance studies were performed using a low frequency impedance technique and the electrochemical surface capacitance was measured by a pulse technique. We have attempted to fit the experimental values to an equivalent circuit model. The Randles' cell circuit with Warburg impedance modeled well the experimental values and the behavior of the enzyme electrodes. The individual components of the model were calculated and the parameters were explained. The blank paste electrode showed a constant phase element behavior.     

Sum frequency generation spectroscopy and double-layer capacitance studies of the 1-butyl-3-methylimidazolium dicyanamide-platinum interface

The orientation of the cation and the anion of 1-butyl-3-methylimidazolium dicyanamide at the platinum-liquid interface, using sum frequency generation (SFG) spectroscopy is reported. Sum frequency spectra at two different polarizations and different potentials are recorded, and analysis of polarization-dependent spectra is performed to estimate the orientation of the dicyanamide anion and the alkyl and ring moieties in the cation as a function of the potential applied to the platinum electrode. In addition, cyclic voltammetry and electrochemical impedance spectroscopy are conducted. A model of the double-layer structure at the electrified interface is presented from the analysis of capacitance and SFG data.     

The use of Metomega Chrome Blue BBL as a metal indicator and its application for the determination of calcium and magnesium in serum

Summary Metomega Chrome Blue BBL was used as a metal indicator for the detection and titration of calcium, magnesium, manganese, nickel and manganese. A displacement reaction was described for the titration of cadmium using Mn-EDTA. A stepwise titration was conducted for the direct titration of both calcium and magnesium in blood serum.Fenugreek mucilage was used as a media for increasing the sensitivity limits of detection of barium, cadmium, cerous, calcium, copper, cobalt, magnesium, manganese, nickel, lead and zinc.     

Non-aqueous cerimetric determination of dithiocarbamates and its application to the determination of amines

A non-aqueous titrimetric method for determination of dithiocarbamates with cerium(IV), is described. The compounds are titrated at room temperature, with visual and potentiometric end-point detection. In visual titrations, the reagent serves as self-indicator and turns the solution yellow at the end-point. Methyl Red can also be used as the indicator. The method has been applied to the determination of amines after their quantitative conversion into dithiocarbamates by reaction with carbon disulphide. The proposed method is accurate to +/- 0.8% with a relative standard deviation of +/- 0.7%.     

三甲氧基苯基荧光酮分光光度法测定锡的研究和应用

研究了新显色剂三甲氧基苯基荧光酮分光光度测定锡的方法。在酸性介质中,表面活性剂吐温 40存在下,试剂与锡形成稳定的橙红色络合物,在510nm处具有最大吸收,其表观摩尔吸光系数ε510=1.48×105L·mol-1·cm-1,锡量在0～0 80μg mL范围内符合比尔定律。方法已应用于铝合金、碳素钢等样品中微量锡的测定。     

Simultaneous Raman spectroscopic and differential double-layer capacitance measurements of pyridine adsorbed on roughened silver electrodes

It is shown that differential double-layer capacitance data can be obtained simultaneously with the recording of the Raman spectra of adsorbates at a roughened silver microelectrode. The use of such data to provide information about the structure of the silver electrode/aqueous KCl (0.1 M)/pyridine (0.1 M) interface is demonstrated.     

The micro-volumetric determination of lead with thionalide and its application to the analysis of tin-base and lead-base alloys

The authors have elaborated an exact micro-volumetric method for the determination of lead with thionalide. The method has been successfully applied to the determination of lead in tin-base and lead-base alloys, following the isolation of lead as lead sulphate and its redissolution in ammonium acetate.     

Borate-polyol complexes in aqueous solution: determination of enthalpies by thermometric titrimetry

Enthalpies for the reaction of borate with 1,2-ethanediol, 1,2-propanediol, 1,2,3-propanetriol and d-mannitol have been determined by thermometric titrimetry. From these enthalpies and equilibrium constants taken from the literature, corresponding entropies have been calculated. The data refer to aqueous solutions at 25 degrees and I = 1.0M (NaNO(3)). The results indicate reasons for the differences in the stabilities of the complexes.     

Spectrophotometric determination of bismuth with semi-xylenol orange and its application in metal analysis

Semi-Xylenol Orange forms a 2 : 1 chelate with bismuth(III), which has a logarithmic value of 3.08 for its conditional formation constant and a molar absorptivity of 4.2 x 10(4) l.mole(-1).cm(-1). Beer's law is obeyed at 540 nm over the range 10-30 mug of Bi(III), with a standard deviation of 1.1 mug (n = 18). Lactic acid is used as an auxiliary complexing agent to prevent olation and oxolation. Interference from up to 1.3 mg of copper can be eliminated by the combined use of masking Cu(II) with thiourea, ascorbic acid and thiosemicarbazide and "post-masking" Bi(III) with sodium chloride. The proposed method has been successfully applied to the direct determination of 0.002% of Bi in lead metal, with a coefficient of variation varying from 3.7 to 6.9%.     

The palladium electrode in aqueous and nonaqueous titrimetry

Two modifications of the palladium-hydrogen electrode of Schwing and Rogers have been made and tested. A new form of “generation” electrode with a vertical palladium diaphragm and fast constant speed circulation has been devised. This form of electrode responds rapidly and has been used in a variety of acid-base titrations in aqueous and nonaqueous systems.