Determination of chloride in sulphuric acid by potentiometric mercurometric titration

The chloride content of concentrated sulphuric acid is determined by mercurometric titration in 80% v/v methanol medium, with a mercury pool as indicator electrode. The method is simple, fast, accurate and reasonably sensitive (limit of detection 4.5 μg/ml), and suitable for routine application.     

The titration error in potentiometric precipitation titration

The titration error can be calculated with the aid of the value of the buffer index determined at the inflection point of the titration curve when a precipitation titration is followed with an ion-selective electrode. When the precipitate is not formed ideally in the titration (i.e., is not formed under equilibrium conditions) the titration error cannot be predicted from the values of the solubility product, nor can the values of the solubility product be calculated from titration data at the inflection point.     

Microcomputer-aided high-speed potentiometric titration system by linear titration plots

Summary An apparatus for high-speed potentiometric titration was assembled and its advantage was demonstrated. Titrant additions were made stepwise in large volumes. The optimum increment volumes were automatically chosen by microcomputer, depending upon the sample concentration. Time intervals between the successive additions were controlled so as to add a new increment immediately after the electrode was equilibrated. On-line calculation of the equivalence volume was conducted based upon linear titration plots, using only four titration points before the equivalence point. The apparatus was capable of determining the concentration of strong and weak monoprotic acids in less than 22s with relative standard deviations of 0.1–0.2%.

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Potentiometrisches Titrationssystem hoher Geschwindigkeit, das auf linearen Titrationskurven beruht und mit einem Mikrocomputer arbeitet

Zusammenfassung Der Aufbau des Geräts wird beschrieben und seine Vorzüge werden diskutiert. Die Zugabe des Titrationsmittels erfolgt stufenweise in großen Anteilen. Die optimalen Volumina werden automatisch je nach Konzentration von einem Mikrocomputer bestimmt. Die Zeitintervalle zwischen den Zugaben werden so gesteuert, daß jeweils nach Gleichgewichtseinstellung der Elektrode eine neue Zugabe erfolgt. Aufgrund linearer Eichkurven erfolgt die online Berechnung des Äquivalenzvolumens, wobei nur vier Titrationspunkte vor dem Äquivalenzpunkt verwendet werden. Mit Hilfe des Gerätes können starke und schwache monoprotische Säuren in weniger als 22 s mit einer relativen Standardabweichung von 0,1–0,2% bestimmt werden.

     

Microtitrimetry by controlled current potentiometric titration

The classical methods of titration require large volumes of chemicals. Microtritimetry is the method of choice since it utilizes small quantities of chemicals and yields less waste compared to other conventional methods. Thus it benefits both the analytical chemists and the environment. In this communication, microtitrimetry is performed by employing the technique of differential electrolytic potentiometry for the location of the end point. Oxidation-reduction titration using platinum electrodes is described. For the first time the endpoint for a sample of 1.0 μL of 0.10 M Fe(II) has been located by titration using a solution of Ce(IV). The optimum conditions such as volume of cerium ammonium sulfate added, current applied to polarize the electrodes in case of dc controlled current potentiometric titration (CCPT). The effect of changing the percentage bias of the square wave used to polarize the electrodes on the differential peak in case of ac CCPT has been investigated. The precision of this microtitrimetric method is also reported.     

The nonaqueous,potentiometric titration of free hydrochloric acid in chloride-containing polymers

The thermal and/or catalytic degradation of chloride-containing polymers causes dehydrohalogenation which produces hydrochloric acid. A nonaqueous method has been developed for the termination of hydrochloric acid. The sample is dissolved in tetrahydrofuran and titrated potentiometrically with a standard tetrabutylammonium hydroxide solution in a 7.5% (V/V) aqueous tetrahydrofuran solution with a combination glass-calomel electrode. The method has a relative precision of ±3.7% at the 95% confidence limit and a sensitivity of 25 ppm HCI.     

Liquid-liquid interfaces as potentiometric ion-sensors-I The n-butanol-water interface as indicating sensor for the potentiometric titration of some acids and bases

The property that liquid-liquid interfaces modify their electrical charge as a function of the composition of the two phases in contact has been used to detect the end-points in a series of acid-base titrations in the aqueous phase. Although the titration curves are not classical in shape, the equivalence points can be located if the solutions are not too dilute. Good results for concentrations down to 10(-3)N have been obtained. The electrode has a fast response. The influence of surface-active substances on the titration has also been investigated.     

自动电位滴定法快速测定钾盐中的钾含量

钾含量的测量常用火焰光度法和四苯硼钾重量法。火焰光度法适用于微量分析 ,对较高含量钾的测定误差较大 ,四苯硼钾重量法的测定准确度高 ,但操作繁琐 ,测定周期长 ,易出错。本文采用四苯硼钠溶液电位滴定法 ,测定高、中含量组分钾 ,测定周期短 ,所用试剂少 ,且不受样品中水不溶物的干扰 ,选择性好 ,测定的准确度和精密度均在 0 .2 %以下 ,适用于钾盐、卤水、复合肥和钾肥中钾的测定。1　实验部分1 .1　仪器和药品ZD 2型自动电位滴定仪 (上海雷磁仪器厂 ) ,PK 1型钾离子选择电极 ,2 1 7型饱和甘汞电极 (双盐桥 )。四苯硼钠标准液 :0 .1mol…     

Gran电位滴定法测定乳酸环丙沙星

介绍了乳酸环丙沙星测定的Gran电位滴定法。采用Gran线性函数进行电位滴定,经图解外推或线性回归处理求出计量点,可直接用于测定乳酸环丙沙星原料药的含量。该法用于多批原料药的测定,结果与药典法基本一致。     

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.

     

Microdetermination of alkaloids in organic solvents by potentiometric titration

A small-intefacial voltaic cell (antimony scratch) is shown to be satisfactory for end-point detection in titrations of various alkaloids and other basic drugs and their salts in ethanol, chloroform or dibutyl ether media with picric acid in the same medium. Small (0.4–4 mg) amounts can be determined. This method has the advantages of being simple and rapid with sharp end-points. The recoveries were 96.52-100.8% for the determinations of 19 drugs and their salts. The relative error was ±5% for five pharmaceutical tablets and injections.     

Critical comparison of evaluation methods of potentiometric titration data using a microcomputer-controlled automatic potentiometric titration system

A microcomputer-controlled automatic potentiometric titrator withP controlled intelligent auto-sampler has been built for serial analysis. Controlling and evaluating programs have also been written. In order to use the most powerful evaluating method, a comparison was made between the methods. The data of the titration curves were obtained by the implicit relation characterizing the curve. The different evaluating methods were tested by using these data. The effects of random errors stemming from measurements were also investigated. The methods used were: two point differentiating formula, differentiation of interpolating and smoothing spline functions, the Gran method, and implicit regression with the Gauss-Newton-Marquardt method. Regression is outstanding among the methods, but it needs much more computing time compared with others. The second-best method is the differentiation with smoothing spline function with end point determination based on finding the sign reversal of the second derivative. This method is much faster than regression.     

Artificial neural networks applied to potentiometric titration of multi-component polybasic acid mixtures

A three-layer artificial neural network model with back-propagation of error is used to treat potentiometric acid-base titration data for estimating the concentrations of individual components in polybasic weak acid mixtures. The network's architecture and parameters were optimized and an empirical rule for dynamically adjusting the learning rate is put forward to improve the network's performance. Satisfactory prediction results were obtained for three-component samples containing maleic acid, propandioic acid and succinic acid with an average relative error of 4.5%.     

The potentiometric titration of fluoride without fluoride ion-selective electrodes

Graphite and platinum sensors were investigated as indicators in the potentiometric titration of fluoride vs lanthanum(III) and thorium(IV). In every case a partially nonaqueous medium yielded larger breaks than in aqueous solution, similar to the fluoride electrode. All the sensors yielded endpoint breaks which were smaller than those obtained with a fluoride ion-selective electrode. The largest breaks were obtained with the vitreous carbon, pyrolytic graphite, and platinum sensors. Conditioning in neutral permanganate solution significantly enhanced the breaks for all types of graphite, except vitreous carbon. The break obtained with the platinum electrode can be enhanced by application of a polarizing current of 2.0 μA in the reducing direction.     

End-point detection in potentiometric titration by continuous wavelet transform

The aim of this work was construction of the new wavelet function and verification that a continuous wavelet transform with a specially defined dedicated mother wavelet is a useful tool for precise detection of end-point in a potentiometric titration. The proposed algorithm does not require any initial information about the nature or the type of analyte and/or the shape of the titration curve. The signal imperfection, as well as random noise or spikes has no influence on the operation of the procedure.The optimization of the new algorithm was done using simulated curves and next experimental data were considered. In the case of well-shaped and noise-free titration data, the proposed method gives the same accuracy and precision as commonly used algorithms. But, in the case of noisy or badly shaped curves, the presented approach works good (relative error mainly below 2% and coefficients of variability below 5%) while traditional procedures fail. Therefore, the proposed algorithm may be useful in interpretation of the experimental data and also in automation of the typical titration analysis, specially in the case when random noise interfere with analytical signal.     

Characterization of di(2-ethylhexyl)thiophosphoric acid by potentiometric titration and capillary zone electrophoresis

 The acidity constant of di(2-ethylhexyl) thiophosphoric acid (DEHTPA) was investigated using potentiometric measurements with a pH glass electrode. Owing to the low solubility of DEHTPA in pure water, its concentration and acidity constants were determined by linearised pH-metric titration in 16.7% ethanol. A K_a value of (2.39±0.08)×10^-4 was obtained. Quantitative determination of DEHTPA was performed by capillary zone electrophoresis (CZE) with carbonate buffer (pH 11.0) as a background electrolyte, operating at −20 kV with direct UV detection at 210 nm. The migration time was 8.97 min and the detection limit was 5 ppm. Received: 2 September 1996/Revised: 19 November 1996/Accepted: 21 November 1996     

Analysis of an electrolyte for gold plating by potentiometric titration

A procedure is developed for determining gold(I) and gold(III) compounds present simultaneously by argentometric potentiometric titration. The procedure is used for the analysis of a hexacyanoaurate-tetrachloroaurate solution for gold plating, to study the nature of different reactions occurring in the preparation of the solution, and to find the quantitative composition of the solution as a function of the preparation conditions.     

Studies on fluorescein-VII The fluorescence of fluorescein as a function of pH

The relative fluorescence of fluorescein over the pH range 3-12 has been measured at 516 nm, with excitation at 489 nm. The relative fluorescence is essentially zero at pH 3, increases slowly between pH 4 and 5, rises rapidly between pH 6 and 7, reaches a maximum at pH 8, and remains constant at above pH 8. The curve of relative fluorescence as a function of pH lies somewhat above the corresponding curve describing the fraction of fluorescein present as the doubly charged anion, Fl(2-), indicating much weaker fluorescence of the singly charged anion, HFl(-), and very much weaker fluorescence by the neutral species, H(2)Fl. The fluorescence data have been used to calculate a value for the third dissociation constant. Because of the complexity of the system, one unknown dissociation constant and three (relative) fluorescence constants, a series of three variable regressions on the data was made. The final values were K(HFl) = 4.36 x 10(-7) (mu = 0.10) for the third dissociation constant and K(H(2)Fl) = 0.8; kappa(HFl) = 5.7; kappa(Fl) = 100.0 for the relative fluorescence constants.