A new automatic recording titrator and its applications

A new type of automatic recording titrator has been developed. The titrant is added intermittently and the titration curve is recorded stepwise, potential changes being registered in the intervals between deliveries of titrant. The increments of titrant and the intervals can be pre-set, but give the best results if controlled automatically during the titration. The end-point and the volume of titrant consumed are read from the recorded titration curve.     

Multicommutated generation of concentration gradients in a flow-batch system for metronidazole spectrophotometric determination in drugs

The titration by using the perchloric acid as titrant and malachite green as indicator is the classical method for the determination of metronidazole, 2-(2-methyl-nitroimidazol-1-yl) ethanol, in drugs. However, this procedure is slow, laborious and consumes great amount of reagents and samples. Moreover, it requires careful manipulation because the reagents cause irritation in the skin and in the eyes. To overcome these drawbacks an automatic system is proposed. It uses three-way solenoids valves, an open chamber and it exploits concentration gradients generated into the chamber in a multicommutated way. As the proposed system embodies the characteristics of flow-batch systems and of multicommutation techniques in flow, it is here named flow-batch-multicommutated titrator. The system is fully controlled by microcomputer running software written in LabView 5.1 graphic language. It processes 60 samples per hour with relative standard deviation smaller than 2.3% (n=6) and in each titration it consumes 2.5 and 1.5 ml of sample and titrant, respectively. By applying the paired t-test, no statistic differences at the 95% probability level between the results of the proposed system and classical titration were observed.     

An automatic titration control unit

A unit is described for the automatic termination of coulometric or volumetric titrations in conjunction with a suitable valve millivoltmeter and motorized buret or constant current generator. Two values of potential can be preset on the instrument, in either rising or falling sequence. On reaching the first potential, the end-point is approached by pulsed addition of the titrant ; the titration is terminated at the second potential, The on and off time cycles for the pulsing circuit are independently variable from 0.1 to 1.0 sec on and 3 to 15 sec off.     

Controlled dynamic titrator

The controlled dynamic titrator described operates with constant titrant flow and time-proportional sample flow; sample and titrant are mixed in a microcell and the equivalence point is reached when the products of the normalities and flow rates of the titrant and the sample are equal. Titration times are measured and printed out. The concentration of the sample is inversely proportional to the titration time. The automatic titrator is discontinuous and suitable for on-line and off-line use. The cycle time of the motor-driven programmer is 2 min. Flow-through detectors for potentiometric, photometric or voltammetric indication can be used for a selection of acid—base and redox titrations. With this equipment, titration of large series of liquid samples with similar contents is simple.     

An automatic back titration method for microchemical analysis

An automatic back titration method for microchemical analysis is introduced, which is based on conventional volumetric analysis's principle and the use of flow injection analysis apparatus for the automation and microminiaturization of the process. The sample and a known, but excess amount of a calibrated reagent solution are injected and propelled into a titration cell, where their reaction takes place. The excess of the reagent is then titrated with a titrant containing an indicator and the end point is monitored photometrically. Since homogeneous mixing in the titration cell is obtained magnetically in the whole process, there is a linear relationship between the analyte's concentration and the volume of the titrant consumed. Nickel in the range of 10-70 g 1(-1) is determined by the above method, in which 30 microl of sample and 500 microl of EDTA are injected and the excess of EDTA is titrated with a standard zinc salt solution containing xylenol orange which could be blocked by nickel ion in a direct titration. This method is characteristic of low sample and reagent consumption, high sampling rate as high as 45 samples h(-1), negligible effect of sample's viscosity, small carry-over effect (lower than 0.14%), and very good precision, whose relative standard deviations are as small as 0.24%.     

A generalized approach for the calculation and automation of potentiometric titrations Part 1. Acid-Base Titrations

Fast and accurate calculation procedures for pH and redox potentials are required for optimum control of automatic titrations. The procedure suggested is based on a three-dimensional titration curve V = f(pH, redox potential). All possible interactions between species in the solution, e.g., changes in activity coefficients and influences of redox potential on pH variations, are taken into account. The number of titrant additions can be reduced considerably without loss of precision, by using the fact that the pH of a protolyte or mixture of protolytes at some fraction titrated does not depend strongly on the actual concentration.     

High precision automated conductometric titrations with the bipolar pulse technique

An automated conductometric titration system has been designed and investigated. Stepper motor driven burets have been constructed to provide precise delivery of small volumes of titrant. A bipolar pulse conductance instrument of wide dynamic range is briefly reviewed as a tool in conductometric titrations. Several types of titrations have been carried out to investigate the accuracy and reproducibility of this apparatus. The precision for titrant volumes of 40µl is ±0.64% relative standard deviation.     

A simple automatic titrator based on a digital balance

A computer-controlled automatic titrator incorporating a weight burette is described. The titration vessel is mounted on the pan of a zero-displacement digital balance which records the weight of added sample as well as the weight of titrant added during the titration.     

Process monitored spectrophotometric titration coupled with chemometrics for simultaneous determination of mixtures of weak acids

A new spectrophotometric titration method coupled with chemometrics for the simultaneous determination of mixtures of weak acids has been developed. In this method, the titrant is a mixture of sodium hydroxide and an acid-base indicator, and the indicator is used to monitor the titration process. In a process of titration, both the added volume of titrant and the solution acidity at each titration point can be obtained simultaneously from an absorption spectrum by least square algorithm, and then the concentration of each component in the mixture can be obtained from the titration curves by principal component regression. The method only needs the information of absorbance spectra to obtain the analytical results, and is free of volumetric measurements. The analyses are independent of titration end point and do not need the accurate values of dissociation constants of the indicator and the acids. The method has been applied to the simultaneous determination of the mixtures of benzoic acid and salicylic acid, and the mixtures of phenol, o-chlorophenol and p-chlorophenol with satisfactory results.     

Tracer-monitored flow titrations

The feasibility of implementing tracer-monitored titrations in a flow system is demonstrated. A dye tracer is used to estimate the instant sample and titrant volumetric fractions without the need for volume, mass or peak width measurements. The approach was applied to spectrophotometric flow titrations involving variations of sample and titrant flow-rates (i.e. triangle programmed technique) or concentration gradients established along the sample zone (i.e. flow injection system). Both strategies required simultaneous monitoring of two absorbing species, namely the titration indicator and the dye tracer. Mixing conditions were improved by placing a chamber with mechanical stirring in the analytical path aiming at to minimize diffusional effects. Unlike most of flow-based titrations, the innovation is considered as a true titration, as it does not require a calibration curve thus complying with IUPAC definition. As an application, acidity evaluation in vinegars involving titration with sodium hydroxide was selected. Phenolphthalein and brilliant blue FCF were used as indicator and dye tracer, respectively. Effects of sample volume, titrand/titrant concentrations and flow rates were investigated aiming at improved accuracy and precision. Results were reliable and in agreement with those obtained by a reference titration procedure.     

A periodic thermometric-titration calorimeter for researching reactions in solution

A titration calorimeter has been built with automatic recording and digital solution volume display; it combines high accuracy in measuring reaction heats with accurate titrant dispensing. The design allows one to replace the titrant during the experiment. The methods reduce the working time considerably by comparison with the usual calorimetric method.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 4, pp. 507–511, July–August, 1988.     

Optimization of the automatic microtitration of chlorides,bromides and iodides

Summary The most favourable conditions for performing the potentiometric micro-scale determination of chlorides, bromides and iodides by their automatic titration with silver nitrate have been investigated. For this purpose, an automatic device has been considered which is able to perform the titrant addition, either for preselected time intervals, or by adjusting them automatically so that the change of potential with time reaches a preselected value.The results obtained indicate that rapid (about two minutes) and accurate titrations can be performed for chlorides with almost all of the parameters chosen, while results affected by a large positive error are obtained for bromides and iodides when the operation modes adopted imply too frequent titrant additions.The weighed samples contain 1.5 to 4 mg halide.     

Titrations using an apparatus for recording the antilogarithm of pH or pM

A titration apparatus plotting either the concentration of sample ion or the concentration of titrant ion has been tested. An antilog apparatus, converting measured e.m.f. values into concentrations is connected to ordinary titration equipment. The instrument has been tested by means of acid—base titrations (titrations of mixtures of weak acids and of a weak and a strong acid), precipitation titrations (determination of the chloride concentration in tap-water, titration of mixtures of halides), titrations with ion-selective electrodes (determination of the fluoride content of toothpaste) and complexometric titrations (determination of copper with EDTA, using mercuric ion as indicator ion and amalgamated silver rod as indicator electrode, or using a copper-selective indicator electrode). The method considerably simplifies the evaluation of the results as compared to conventional potentiometric titrations.     

The analysis of anhydrous titanium trichloride

Titrimetric determinations of titanium and chloride were examined for their suitability in establishing the stoichiometry of titanium trichloride. Aluminium metal reduction of titanium(IV) to titanium(III) in aqueous sulphuric acid solution gave higher precision than the Jones Reductor procedure ; in both cases exceptional care was necessary before titration in order to prevent some reoxidation of reduced titanium by dissolved oxygen in the titrant. Deaerating the ferric alum titrant and delivering it under nitrogen made it possible to obtain a virtually complete titanium recovery. A convenient apparatus is described. A procedure is also described for the elimination of interference in the Volhard chloride determination due to the presence of high concentrations of titanium sulphate and of gelatin used for sample encapsulation.     

Maßanalyse und Katalyse

The application of automatic titration instruments for volumetric determinations using catalytic indicator reactions is described. Examples for a photometric (Mn²⁺ with EDTA), potentiometric (Hg²⁺ and Ag⁺ with KI, I^? with Hg²⁺) and biamperometric (Cu²⁺ with EDTA) regulation of the automatic titrator are given. In some of these methods, contrary to the usual way, it is the inhibitor which serves as a titrant (“titration with the brake”) and not the catalyst.     

Reaktion von Vanadium(IV) mit 3′-Pyridylfluoron und seine photometrische Bestimmung

The application of automatic titration instruments for volumetric determinations using catalytic indicator reactions is described. Examples for a photometric (Mn²⁺ with EDTA), potentiometric (Hg²⁺ and Ag⁺ with KI, I^? with Hg²⁺) and biamperometric (Cu²⁺ with EDTA) regulation of the automatic titrator are given. In some of these methods, contrary to the usual way, it is the inhibitor which serves as a titrant (“titration with the brake”) and not the catalyst.     

Acid-base titrations by stepwise addition of equal volumes of titrant with special reference to automatic titrations-III Presentation of a fully automatic titration apparatus and of results supporting the theories given in the preceding parts

This paper forms Part III of a series in which the first two parts describe methods for evaluating titrations performed by stepwise addition of equal volumes of titrant. The great advantage of these methods is that they do not require an accurate calibration of the electrode system. This property makes the methods very suitable for routine work. e.g., in automatic analysis. An apparatus for performing such titrations automatically is presented. Further, results of titrations of monoprotic acids, a diprotic acid, an ampholyte, a mixture of an acid with its conjugate base, and mixtures of two acids with a small difference between the stability constants are given. Most of these titrations cannot be evaluated by the Gran or Hofstee methods but yield results having errors of the order of 0.1% if the methods proposed in Parts I and II of this series are employed. The advantages of the method of stepwise addition of equal volumes of titrant combined with the proposed evaluation methods, in comparison with common methods such as titration to a preset pH, are that all the data are used in the evaluation, permitting a statistical treatment and giving better possibilities for tracing systematic errors.     

Photochemical redox titrations with tungsten(V)

A titration method has been developed for the determination of micromolar quantities of dichromate, vanadate and hexacyanoferrate(III) with in situ photochemical generation of tungsten(V) as the titrant. Precision of 1–3% was obtained. Spectrophotometric end-points were utilized because of the intense blue color of the titrant (λ_max 770nm; _max7.10³). Because the titrant reacts with oxygen, a closed, argon-flushed, circulating photolysis apparatus was constructed. Optimal solution condi- tions were investigated ; tungsten reagent must be added as the solid just before titra-tion. An induced reaction between dichromate and glucose was found, but satisfactory linear calibration curves were obtained. With reduced photolytic intensity, 0.2 μeq of dichromate can be determined.     

络合体系中的相对滴定法及其应用于铝的测定

本文提出了络合体系中的相对滴定分析法，它以滴定到一定的状态时，滴定剂体积与被测物的基之间的线性关系为定量基础，用仪器分析的定量方法进行定量，适应于所有类型的络合体系，即使对滴定突跃很小或根本无突跃的体系也同样适用。用氟离子滴定铝离子的实验结果表明本方法的精密度很高。一般相对误差小于0．1％。即使对于铝离子的量小到10-7mol／L时，在最佳实验条件下的相对误差也不大于0．2％。该方法既具有滴定分析法的高精密度，又具有仪器分析法可以测量微量物质的优点，并且设备和方法简单。     

Computer-controlled titrations: Part 1. Considerations based on systems theory

Automated titrimetric procedures are considered on the basis of systems theory, with emphasis on the dynamic behaviour of the system. In the case of continuous addition of titrant, conditions are derived for the maximum addition speed and a correction procedure is given. Control algorithms for discontinuous addition of titrant are given, including an algorithm for on-line estimation of the dynamic (overall) effects of the titration system; this is useful for determining the waiting time between two successive additions of titrant. Shannon's theorem is utilized in order to decide on the sampling of the titration curve, both for continuous and discontinuous additions of titrant. Finally, confidence intervals for the end-point determination are derived, based on zero crossing statistics, and applied on the second derivative of a sigmoidal titration curve.