Theory and practice of electrochemical titrations with dual microband electrodes

Dual parallel microband electrodes, operated as a generator–collector pair and made by a simple, inexpensive mass-production method, have been used to implement a ‘titration’ method. The solution contains the electro-inactive analyte and a reagent from which the titrant can be generated electrochemically. The galvanostatically generated titrant is detected at the collector amperometrically. The collection efficiency is affected by the reaction between the titrant and the analyte. Determination of ascorbic acid by titration against ferricyanide is given as an example. The measurement is performed as follows: After application of the collector potential, the boundary conditions between measurements are renewed by a quick pulsed motion of the electrode assembly. Then the generator current is applied. Following an initial delay, the collector current increases as t^1/2, with slope and collection efficiency dependent on analyte concentration. This results in a fast and effective method for implementing some standard titration methods without the need for accurate volume measurement and reagent preparation. The accuracy is determined by the reproducibility of electrodes. The present work shows concentration measurements in the mM scale to ≈±10%, in a time of a few seconds. The highly stable extrapolation method used for numerical simulation of the generator–collector experiment, which takes into account the non-uniform current distribution over a microband electrode with a galvanostatic boundary condition, is developed using a conformal map. A good agreement between simulations and experimental results was obtained in voltammetric, potential step and generator–collector measurements. It is shown that a useful approximate calculation can be made rather easily by representing the problem in terms of a reaction layer in the conformal space.     

硼酰化钴中硼的快速测定

硼酰化钴中硼的测定采用EDTA作为钴的络合掩蔽剂,消除了钴对测定硼的影响。同时改用溴甲酚绿-甲基红-酚酞三元混合指示剂作为测定硼的指示剂,使滴定终点灵敏、准确。建立了一种测定硼酰化钴中硼含量的简便、快速的分析方法。     

Potentiometric determination of sulphur in secondary alumina

Summary A procedure for determination of sulphur in adsorbates based on combustion of samples in a high-frequency induction furnace, and subsequent registration by potentiometric titration in an alcoholic medium is described. Optimum conditions for the titration are discussed. A new type of indicator electrode with integrated impedance transformation electronics has been used. The technique was applied with good results to samples of secondary alumina (standard deviation 0.01%).

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Potentiometrische Bestimmung von Schwefel in sekundärem Aluminiumoxid

Zusammenfassung Das beschriebene Verfahren zur Schwefelbestimmung in Adsorbaten beruht auf der Verbrennung der Probe in einem Hochfrequenz-Induktionsofen und nachfolgender potentiometrischen Titration in alkoholischem Medium. Die optimalen Titrationsbedingungen werden diskutiert. Es wurde eine neuartige Indicatorelektrode mit integrierter Impedanztransformation benutzt. Bei der Anwendung auf sekundäres Aluminiumoxid wurden gute Ergebnisse erzielt (Standardabweichung 0,01%).

     

Amperostatische Coulometrie von Ferrocen und seinen Derivaten in Acetonitril

Zusammenfassung Zur amperostatischen Coulometrie von Ferrocenen wird Cu(I)BF₄ als Hilfsstoff zugegeben, da Ferrocen sich leicht durch Cu(II)(BF₄)₂ oxidieren läßt. Der Verlauf der Titration wird biamperometrisch verfolgt. Die Proben enthalten nur wenige Milligramme der betreffenden Verbindungen. Die Resultate sind zufriedenstellend.

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Amperostatic coulometry of ferrocene and its derivatives in acetonitrile

Summary Cu(I)BF₄ was added as an auxiliary substance as Cu(II) (BF₄)₂ can bring about the oxidation of ferrocene. The advancement of the titration was followed by means of biamperometry. The samples contained a few milligrams of the compounds concerned and the results were satisfactory.

     

Precise potentiometric titration of manganese

Summary A method for the precise automatic potentiometric titration of manganese is described. Manganese ions are titrated with permanganate as a titrant in fluoride medium. The ideal quantity to titrate is about 30 mg of manganese. The endpoint of the reaction is recorded automatically. By adding more than 98% of the titrant by weight and the remaining part by means of an automatic burette the precision of the method could be improved to 0.03%. Systematic deviations are eliminated by calibrating the reagent with well-known reference solutions.

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Genaue potentiometrische Manganbestimmung

Zusammenfassung Mangan wird mit Permanganat in Fluoridmedium titriert. Die optimale Menge für die Titration beträgt etwa 30 mg Mn. Der Endpunkt der Reaktion wird automatisch registriert. Durch Zusatz von mehr als 98% des Titrationsmittels als Einwaage und Vervollständigung der Reaktion mit Hilfe einer automatischen Bürette kann eine Genauigkeit von 0,03% erzielt werden. Systematische Fehler werden durch Eichung mit bekannten Referenzlösungen vermieden.

     

基于质子条件式的终点误差精确式

容量分析中,滴定终点的误差决定了该分析方法的可靠性。根据质子条件式,可推导出终点误差的精确式。该表达式用滴定开始前而不是终点时物质的浓度进行计算;用滴定终点时的p H进行计算,不需要计算化学计量点时的p H;所得出的精确式具有通用性,能有效降低学习与记忆的难度,提高计算结果的准确度。     

An automatic system for acidity determination based on sequential injection titration and the monosegmented flow approach

An automatic sequential injection system, combining monosegmented flow analysis, sequential injection analysis and sequential injection titration is proposed for acidity determination. The system enables controllable sample dilution and generation of standards of required concentration in a monosegmented sequential injection manner, sequential injection titration of the prepared solutions, data collecting, and handling. It has been tested on spectrophotometric determination of acetic, citric and phosphoric acids with sodium hydroxide used as a titrant and phenolphthalein or thymolphthalein (in the case of phosphoric acid determination) as indicators. Accuracy better than |4.4|% (RE) and repeatability better than 2.9% (RSD) have been obtained. It has been applied to the determination of total acidity in vinegars and various soft drinks. The system provides low sample (less than 0.3 mL) consumption. On average, analysis of a sample takes several minutes.     

Assay of Bicarbonate Content in Certain Effervescent Formulations

Abstract

A quantitative method was developed for the assay of the bicarbonate content in a number of potassium-replacement effervescent tablets with citric acid. The method involved treatment of an aliquot of the crushed tablet with water, then with 0.5 N sulfuric acid, followed by quantitative absorption of the liberated carbon dioxide into 0.2 N sodium hydroxide in a closed system with a calcium chloride-protected vent. The sodium carbonate-sodium hydroxide solution was subjected to a two-step titration with standard acid using phenolphthalein and bromophenol blue indicators for the first and second step, respectively. Overall percent recovery (± SD) of potassium bicarbonate from simulated tablets were: 99.6 ± 0.9% (n = 4); in presence of potassium citrate, 100.0 ± 1.3% (n = 4); and in presence of potassium chloride and L-lysine hydrochloride, 101.5 ± 1.9% (n = 3). Application of the method to commercial products near the expiration date showed potassium bicarbonate contents of 80–90% of label claim. The method may be applied to the assay of any bicarbonate salt in other effervescent formulations.     

Theory of Precision in Linear Titration Curves

Abstract

Error propagation in linear titration methods are considered in terms of the precision in measurement of the slopes and intercepts of the titration curve. Simulated curves including random errors were analyzed. The results indicate that the analytical precision is independent of the angle between the curves when the difference in slopes in fixed.     

EDTA滴定法测定草酸中硫酸根

在马弗炉(200℃)灼烧至草酸全部挥发,滴加(1 1)盐酸,使刚果红试纸由红变蓝色(或调节pH到4左右),除去二氧化碳。加入钡镁混合液,沉淀6h(或放置过夜)。加入(1 1)氨水调节pH值约为8—9,加入10mL氨-氯化铵缓冲溶液,2滴铬黑T指示剂,用EDTA标准溶液滴定SO2-4含量。