Electrochemical reduction of sodium metavanadate in an equimolar KCl-NaCl melt

Electrochemical reduction of sodium metavanadate in an equimolar KCl-NaCl melt and the effect of acid-base properties of environment on this process are studied by a voltammetry method on a stationary platinum electrode. It is established that the limiting current of the NaVO₃ electroreduction process has a kinetic nature. The process proceeds via an autoinhibition scheme and its rate is limited by an acid-base reaction conjugated with an irreversible charge transfer reaction. A substantial role of cationic composition of the melt is revealed experimentally. Following acidification of the KCl-NaCl-NaVO₃ melt by Mg²⁺ (from MgCl₂), the process passes from an irreversible kinetic regime into a reversible diffusion (quasi-diffusion) process. Values of stability constants for vanadates produced with the aid of acid-base titration of vanadium pentoxide by oxygen ions in experimental conditions are presented. These values are taken into account when calculating kinetic parameters of the NaVO₃ electroreduction.     

Nonionic surfactant-selective electrode and its application for determination in real solutions

A liquid membrane nonionic surfactant sensitive electrode has been prepared, based on a new barium pseudocationic complex of a highly ethoxylated fatty alcohol polyglycol ether and tetraphenylborate as sensing material. The complex has been incorporated into the plasticized PVC-membrane and used as sensing material.The electrode exhibited positive linear non-Nernstian response toward different nonionic surfactants and sub-Nernstian response toward tetraphenylborate with the lower detection limit of 3.3 × 10⁻⁷ mol dm⁻³ in barium chloride solution.The interfering effect of some alkaline, alkaline earth, and heavy metal cations, has been demonstrated by displaying their calibration curves compared with that of Triton X-100.The electrode has been used as an end-point indicator for potentiometric titration of analytical and technical grade polyethoxylated nonionic surfactants, modelled detergent products, and commercial detergents.     

The thermodynamic dissociation constants of the anticancer drugs camptothecine, 7-ethyl-10-hydroxycamptothecine, 10-hydroxycamptothecine and 7-ethylcamptothecine by the least-squares nonlinear regression of multiwavelength spectrophotometric pH-titration data

The mixed dissociation constants of four anticancer drugs - camptothecine, 7-ethyl-10-hydroxycamptothecine, 10-hydroxycamptothecine and 7-ethylcamptothecine, including diprotic and triprotic molecules at various ionic strengths I of range 0.01 and 0.4, and at temperatures of 25 and 37 °C - were determined with the use of two different multiwavelength and multivariate treatments of spectral data, SPECFIT32 and SQUAD(84) nonlinear regression analyses and INDICES factor analysis. A proposed strategy for dissociation constants determination is presented on the acid-base equilibria of camptothecine. Indices of precise modifications of the factor analysis in the program INDICES predict the correct number of components, and even the presence of minor ones, when the data quality is high and the instrumental error is known. The thermodynamic dissociation constant was estimated by nonlinear regression of {pK_a, I} data at 25 and 37 °C: for camptothecine and 3.02(8), and 10.23(8); for 7-ethyl-10-hydroxycamptothecine, and 2.46(6), and 8.74(3), and 9.47(8); for 10-hydroxycamptothecine and 2.84(5), and 8.92(2), and 9.98(4); and for 7-ethylcamptothecine and 3.30(16), and 10.98(18). Goodness-of-fit tests for various regression diagnostics enabled the reliability of the parameter estimates found to be proven. Pallas and Marvin predict pK_a being based on the structural formulae of drug compounds in agreement with the experimental value.     

Galvanic cell without liquid junction for potentiometric determination of copper

This paper describes potentiometric measurements in an integrated galvanic cell with both indicator and reference electrodes. Both electrodes are conducting polymer-based. The copper-sensitive indicator electrode is made by using poly(3,4-ethylenedioxythiophene) (PEDOT) doped with 2-(o-arsenophenylazo)-1,8-dihydroxynaphthalene-3,6-disulphonic sodium salt (Arsenazo-I) as the electroactive substance in the film, while the reference electrode is based on PEDOT doped by 2-morpholineoethanesulfonic acid (MES). It is shown that the galvanic cell can be used for determination of copper both in non-aqueous media (where all PVC-based membranes failed) and in the presence of chloride ions, which disturb the signal of conventional copper ion-selective electrodes with solid-state membranes. It is further shown that the titration of copper ions can be successfully monitored using the described electrochemical cell.     

Chemical analysis of acidic silicon etch solutions: I. Titrimetric determination of HNO3, HF, and H2SiF6

The chemical etching of silicon using HF-HNO₃ mixtures is a widely used process in the processing of silicon wafers for microelectronic or photovoltaic applications. The control of the etch bath composition is the necessary condition for an effective bath utilization, for the replenishment of the consumed acids, and to maintain a certain etch rate. The present paper describes two methods for the total analysis of the individual etch bath constituents HF, HNO₃, and H₂SiF₆. Both methods start with an aqueous acid-base titration determining the total acid concentration and the concentration of H₂SiF₆. The first method is an acid-base titration using a 0.1 mol L⁻¹ methanolic solution of cyclohexylamine (CHA) as non-aqueous titrant to determine the content of nitric acid. Then, the amount of hydrofluoric acid is calculated from the difference between the total acid and nitric acid content. The second method is based on the determination of the total fluoride concentration using a fluoride ion-selective electrode (F-ISE). The content of hydrofluoric acid is obtained from the difference between the total fluoride content and the amount of fluoride bound as H₂SiF₆. The amount of nitric acid results finally calculated as difference to the total acid content.     

Direct analysis of bottom sediments by a microcoulometric titration method for determination of total organic halide pollutants

Up to now the content of the organic halides in sediments was measured as extractable organic halides compounds by different methods including microcoulometric titration one. We describe a procedure for microcoulometric determination of total organic halide pollutants by using a direct combustion of the sediments into the microcoulometric system furnace. An accelerated removal of the inorganic chlorides by reaction with potassium nitrate using ultrasonic radiation was attained. The procedure was validated for analysis of bottom sediments from natural and anthropogenic sources. The repeatability RSD = 8.5%, the expanded relative uncertainty U (n = 7, P = 95%, k = 2) = 6.4%, the reproducibility RSD was within the range 10.0–7.3%, the average recovery R = 97.6% and method LOD = 11 mg kg⁻¹ Cl. Correspondence: Zara V. Aneva, Analytical Department, University “Prof. Dr. Assen Zlatarov”, Nr. 1 Prof. Yakimov street, 8010 Bourgas, Bulgaria     

Polyacrylamide and poly(itaconic acid) complexes

Intermolecular complex formation through hydrogen bonding between poly(itaconic acid), partially neutralized and non-neutralized, and polyacrylamide was studied by potentiometry. The complexes were obtained by template polymerization of itaconic acid and partially neutralized itaconic acid on polyacrylamide as a template. All the complexes were characterized by elemental analysis, FTIR spectroscopy and thermal analysis.     

用自动凯氏定氮仪测定水中氨氮

用MgO控制预蒸馏水中的pH值,以硼酸溶液为吸收液,用稀硫酸进行中和滴定,用自动凯氏定氮仪测试水中的氨氮,检测下限为1mg/L,相对标准偏差在0.32%~1.04%范围内,加标回收率为96%~104%,并将该法与纳氏试剂比色法和离子色谱法进行了比较。     

Compatibility and stability tests of risperidone with soft-drinks by isothermal titration microcalorimetry

Isothermal titration microcalorimetry has been applied to investigate the compatibility testing of risperidone oral solution with soft-drinks and the interaction with tea tannin such as (–)-epigallocatechin, (–)-epicatechin, theaflavin and their gallates. In aqueous solution, risperidone was exothermically bound to tea tannin with binding affinity (10³–10⁴ M^–1), small enthalpy and entropy changes reflecting van der Waal’s interaction to form an insoluble complex at 1:1 molar ratio. The heat effect of risperidone titrated into soft-drinks containing tannin was exothermic and proportional to the quantity of the complex. While, no significant heat effect was found for risperidone titrated into a pet-bottled water and an infusion of parched barley without tea tannin. These results were agreed with stability testing of risperidone in some soft-drinks by HPLC method.     

Effect of External Acidity of Mordenite-Supported Catalysts on the 2,2-Dimethylbutane Content in Hydroisomerization Products of n-Hexane

We have used potentiometric titration with tetrabutylammonium hydroxide to determine the acid center content on the outer surface of dealuminated natural and synthetic mordenites. We have established a symbatic relationship between the 2,2-dimethylbutane content in the hydroisomerization products of n-hexane on dealuminated palladium-containing mordenites and the number of their external acid centers. We have studied the possibility of partial deactivation of such centers during ion-exchange deposition of palladium on the catalysts, using a tetraammine palladium solution.