A conductometric method for colloid titrations

A negative or positive colloid sample solution can be directly titrated, respectively, with a polycationic (poly-N, N-diallyldimethylammonium chloride) or polyanionic (potassium polyvinylsulfate) titrant to a conductometric end-point. With the conventional toluidine blue indicator method a positive colloid solution is titrated directly with a polyanionic titrant, but a negative colloid solution must be treated with an excess of a polycationic titrant, which is back-titrated with the polyanionic titrant. For positive colloid solutions, both indicator and conductometric methods are suitable; for negative colloids the conductometric method is preferable because of its constant titration vlues over a range of pH values.     

Potentiometric flow titration of iron(II) and chromium(VI) based on flow rate ratio of a titrant to a sample

A new potentiometric flow titration has been proposed based on the relationship of the flow rates between titrant and sample solutions. A sample solution is pumped at a constant flow rate. The flow rate of the titrant solution is gradually increased at regular time intervals and a flow rate for the titrant solution in the vicinity of the equivalence point is obtained. The concentration of the sample is calculated by C(S) (mol l(-1))=(R(T) (ml min(-1))xC(T) (mol l(-1)))/R(S) (ml min(-1)), where C(S), C(T), R(S), and R(T) denote the unknown sample concentration, titrant concentration in the reservoir, the flow rate of the sample solution which is a constant rate, and the flow rate of the titrant solution at an inflection point, respectively. The potentiometric flow titration of iron(II) with cerium(IV) and of chromium(VI) with iron(II) has been presented. The titration time of the proposed method is about 10 min per sample. An R.S.D. of the method is 0.77% for seven determinations of 1x10(-3) mol l(-1) iron(II). Similarly, the flow titration of chromium(VI) with iron(II) is carried out over the range 1x10(-4)-1x10(-3) mol l(-1) chromium(VI) and is successfully applied to the determination of chromium in high carbon ferrochromium.     

Choice of chemical conditions in order to obtain linear titration curves in potentiometry

In the titration of an acid HA with a strong base, [HA] diminishes, on the whole, in proportion to the addition of titrant. However, [HA] = K_HA[H] [A], and if [A] is kept constant [HA] will be proportional to [H]. Therefore if [H] instead of [HA] is plotted against ml of titrant added, one obtains a linear titration curve. [A] is kept constant by addition of NaA before titration in such high concentration that the formation of A can be neglected during the titration. When an acid stronger than acetic acid is titrated, sodium acetate can be used as the added salt. Even mixtures of adds, mono- or polybasic, then yield'straight titration curves since one is in fact titrating acetic acid in the presence of excess of acetate. For weaker acids sodium sulphite is used. In the oxidation-reduction titration of, for example, ferrous iron with permanganate, the potential measured is dependent on the ratio [Fe²⁺]/[Fe³⁺]. If [Fe³⁺] is kept constant by the addition of ferric chloride before the titration, the potential win be dependent only on [Fe²⁺]. Since this diminishes in proportion to the added volume of titrant, straight titration curves can be obtained in this case also. No correction for dilution should be made.     

固定pH滴定法测定弱酸弱碱性药物

报道一种水溶液吕测定弱酸弱碱性药物的新型滴定分析方法－固定ｐＨ滴定法，其理论基础是弱酸弱碱在水溶液中各种存在形式的分布系数在ｐＨ值固定时为常数，对甲硝唑，盐酸美西律等离散常数在１０＾－８至１０＾－１１范围内的７种弱酸弱碱性药物进行测定。结果与药典法吻合，回收率在９９．４％～１００．６％，方法简便，快速，准确，制剂中的赋形剂及色物不影响测定。     

恒电位氟-铝配位滴定法测定铝的研究

以氟离子溶液作滴定剂,氟离子选择性电极作指示电极,对恒电位配位滴定法测定铝进行了研究,导出了该测定法的计算模型。测定结果的准确度受电位的控制误差对滴定剂体积误差的影响及滴定剂体积的相对误差两个因素影响。在滴定的中间位置,准确度比较高。随着滴定剂体积的增加,测定的灵敏度增加。方法可用于金属铝及锌一铝合金中铝的测定。     

Potentiometric titrations using dual microband electrodes.

We present a novel method of analysis using potentiometric end-point detection and dual microband electrodes in generator-collector mode. The titrant is electrogenerated using either a constant current or a current that increases linearly with time, and the fluxes of reactive material rather than molar amounts are balanced. The advantage of the ramp current system over the constant current method is that all of the information needed for a full titration curve and a proper analysis can be obtained during a single scan. The method was applied to the determination of vitamin C with ferricyanide and to the determination of thiosulfate and sulfite with iodine using gold microband electrodes. As a new type of analysis, a potentiometric titration that uses dissolving silver microband electrodes in order to generate the titrant is demonstrated. The system was applied to the detection of chloride, iodide, thiosulfate and cyanide. The accuracy of the analysis is +/-10%, limited mainly by the present screen-printing process, and the method is well adapted for measurements on the millimolar scale.     

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.     

Formula for the equivalence volume in potentiometric titration. As illustrated by the microdetermination of organohalogens with ion-selective electrode

An equation for calculating the equivalence volume in potentiometric titration is suggested. The derivation of this equation is illustrated by the potentiometric titration of halide with incremental addition of the titrant silver nitrate. The equation is generally applicable to any potentiometric titration involving a simple and rapid reaction whose Nernstian response is constant. It is proposed to utilize it for common microdeterminations involving ion-selective electrodes.     

非水滴定法测定酰胺缩醛

对非水滴定酰胺缩醛的溶剂、滴定剂和指示剂进行了选择试验，用ＨＣｌ甲醇标准液进行滴定，通过电位滴定曲线或甲基橙指示剂可以准确的确定滴定终点，方法简便，结果准确。     

Thermometric and potentiometric titrations of modified glass surfaces

Glass surfaces modified with N-2-aminoethyl-3-aminopropyltrimethoxysilane have been titrated with copper(II) by constant rate thermometric titration and by manual potentiometric titration with Gran plot end-point location. The results indicate that the titrant reacts with the bound ligand in a two-step process, with the thermometric titration responding to the first step and the potentiometric titration responding to the combined steps.     

Ion-selective electrodes in potentiometric titrations; a new method for processing and evaluating titration data

A new method to convert the potential of an ion-selective electrode to concentration or activity in potentiometric titration is proposed. The advantage of this method is that the electrode standard potential and the slope of the calibration curve do not have to be known. Instead two activities on the titration curve have to be estimated e.g. the starting activity before the titration begins and the activity at the end of the titration in the presence of large excess of titrant. This new method is beneficial when the analyte is in a complexed matrix or in a harsh environment which affects the properties of the electrode and the traditional calibration procedure with standard solutions cannot be used. The new method was implemented both in a method of linearization based on the Grans's plot and in determination of the stability constant of a complex and the concentration of the complexing ligand in the sample. The new method gave accurate results when using titrations data from experiments with samples of known composition and with real industrial harsh black liquor sample. A complexometric titration model was also developed.     

Mechanism and reaction rate of the karl fischer titration reaction: Part V. Analytical Implications

The Karl Fischer titration procedure for the determination of water has been studied. In view of the results of previous investigations, a methanolic sodium acetate—sulfur dioxide solution is recommended as solvent and an iodine solution in methanol as titrant. The advantages of this procedure over a conventional Karl Fischer titration are: a much more rapidly reacting reagent, the possibility of a visual end-point detection, a titrant of constant titre over a long period of time, and the absence of the disagreeable odour of pyridine.     

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.     

Coulometric titration with air transported sample

Air transported samples of a mixture containing the analyte and a supporting electrolyte are consecutively propelled into a microconduit system through a titration cell, a coil and a detector cell. Different amounts of electrochemically generated titrant are obtained in the separate samples while they are passing through the titration cell. Various quantities of the titrant are achieved by changing the duration of the titrant generating process that is done by various time for the sample solution staying in the titration cell (different sample movement rate). The titrated sample is then homogenised in the coil and detected in an electrochemical detector cell that supplies necessary data for the analyte determination. The declared method is experimentally verified on coulometric titration of hydrochloric acid (HCl) with electrogenerated sodium hydroxide and a titration of aniline with bromine generated in a bromide solution.     

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.     

A simple photo-electric carbon dioxide titrator

A simple photo-electric apparatus is desscribed for the automatic titration of small amounts of carbon dioxide The apparatus is based on automatic titrant shut-off controlled by a photoresistor and is used for the non-aqueous titration proposed by Blomet al. (pyridine/monoethanolamine medium, sodium methanolate titrant).     

Some theoretical considerations in analytical chemistry : A method of calculating asymmetrical titration curves avoiding the use of cubic equations

A method is offered for the exact calculation of data for unsymmetrical titration curves in which the solution of cubic equations is avoided. Instead of calculating ion concentrations from the volume of titrant added in the conventional way, the calculation is reversed, and titrant volumes are calculated from supplied values of the ion which is not in excess. The necessary precision is attained more easily by calculating the difference between the titrant volume and the equivalence point volume, so that the use of seven figure logarithms is unnecessary.     

Determination of sulphuric acid in process effluent streams using sequential injection titration

Sulphuric acid in process effluent streams from an electrorefining copper plant was analysed with a sequential injection (SI) titration system using sodium hydroxide as titrant. In the proposed SI titration system a base titrant, acid analyte and base titrant zone were injected sequentially into a distilled water carrier stream in a holding coil and swept by flow reversal through a reaction coil to the detector. The base zones contained bromothymol blue as indicator and the endpoint was monitored spectrophotometrically at 620 nm. The influence of carrier stream flow rate, acid and base zone volumes and titrant concentration on the linear range of the method was studied to obtain an optimum. A linear relationship between peak width and logarithm of the acid concentration was obtained in the range 0.006-0.178 mol l(-1) of H(2)SO(4) for a NaOH concentration of 0.002 mol l(-1). The results obtained for the SI titration of process samples were in good agreement with a standard potentiometric method with an RSD<0.75% and a sample frequency of 23 samples h(-1).     

Potentiometric back-titration of sulfate ion using a tetraphenylborate derivative as a titrant and a titrant-sensitive plasticized poly(vinyl chloride) membrane electrode

A potentiometric back-titration method for the determination of sulfate ions using a plasticized poly(vinyl chloride) membrane electrode without added ion-exchanger is described. A solution of a derivative of tetraphenylborate is used as titrant. The method is based on the ion association between an excess of 2-aminoperimidinium added to the sulfate containing sample and the tetraphenylborate derivative in the titrant. The titration end-point is detected as a sharp potential change due to an increase in the concentration of the free tetraphenylborate derivative at the equivalence point. The sharpness of the titration curve at the end-point is compared for two tetraphenylborate derivatives. Good results are obtained with a solution of sodium tetrakis (4-fluorophenyl) borate.     

Potentiometric titration of anionic polyelectrolytes using a cationic surfactant solution as a titrant and a titrant-sensitive plasticized poly(vinyl chloride) membrane electrode

A potentiometric titration method for the direct determination of anionic polyelectrolytes using a plasticized poly(vinyl chloride) membrane electrode is described. A cationic surfactant solution is used as titrant. The method is based on ion association between the anionic polyelectrolyte in the sample and the cationic surfactant in the titrant. The end-point is detected as a sharp potential change due to an increase in the concentration of the free cationic surfactant at the equivalence point. The sharpness of the titration curve at the end-point is compared for several cationic surfactants; a solution of stearyltrimethylammonium ion has been found to be superior. Received: 8 October 1996 / Revised: 17 December 1996 / Accepted: 18 December 1996