Photometric complex-formation titrations of submicromole amounts of metals in the presence of an approximately equivalent amount of indicator

The photometric titration of the metal indicator complex MI with a ligand L is discussed. A tangent procedure is adopted for the determination of the end-point. From this procedure, in combination with an assumed maximum titration error, titration conditions have been derived. A procedure is introduced which, in conjunction with the derived titration conditions, permits the selection of a suitable titration medium by means of a diagram in which log K, log alpha and log chi are plotted vs. pH. The procedure is applied to determination of lead and zinc in the presence of citric acid, the medium used for their paper-electrophoretic separation. The use of citric acid introduces some limitations; it is shown that the method developed is generally applicable.     

Determination of quaternary ammonium compounds by potentiometric titration with an ionic surfactant electrode: single-laboratory validation

A potentiometric titration for determining the quaternary ammonium compounds (QAC) commonly found in antimicrobial products was validated by a single laboratory. Traditionally, QACs were determined by using a biphasic (chloroform and water) manual titration procedure. Because of safety considerations regarding chloroform, as well as the subjectivity of color indicator-based manual titration determinations, an automatic potentiometric titration procedure was tested with quaternary nitrogen product formulations. By using the Metrohm Titrando system coupled with an ionic surfactant electrode and an Ag/AgCl reference electrode, titrations were performed with various QAC-containing formulation products/matrixes; a standard sodium lauryl sulfate solution was used as the titrant. Results for the products tested are sufficiently reproducible and accurate for the purpose of regulatory product enforcement. The robustness of the method was measured by varying pH levels, as well as by comparing buffered versus unbuffered titration systems. A quantitation range of 1-1000 ppm quaternary nitrogen was established. Eight commercially available antimicrobial products covering a variety of matrixes were assayed; the results obtained were comparable to those obtained by the manual titration method. Recoveries of 94 to 104% were obtained for spiked samples.     

非终点滴定法与其应用

为了实现滴定分析的快速和自动化,本文借鉴以往研究的经验针对其不足[1~8],提出了一种新的分析方法,滴定中只要加二次标准液,将采集到的数据通过适当的数学计算,即可得到样品液的浓度,本法不需要已知反应常数、电极转换系数等,对中和度没有严格要求[9~11],故具有可操作性和实用性。本法不需要确定终点,不需要全过程滴定,为滴定分析的自动、快速化提供了充分的条件,特别适合冶金、环境、食品、药品的大批量快速分析和在线分析。根据该方法的原理即可开发出一种新的自动分析仪。     

Activity Coefficients of Individual Ions from Titration Data

It is shown that the activity coefficients of the anions resulting from the dissociation of a weak polyprotic acid can be obtained from titration data. Activity coefficients are determined in terms of the activity coefficient of the undissociated acid. The extracted activity coefficients are also dependent on the pH scale adopted in the titration process and are considered as operational coefficients. The computational procedure uses an exact equation representing the titration curve and a nonlinear least-squares fitting procedure. As an illustration, the activity coefficients of the anions of succinic acid are determined. The method also allows study of the variation of the activity coefficients with the ionic strength in a straightforward manner.     

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.     

Novel Integrated Flow-Based Steam Distillation and Titration System for Determination of Volatile Acidity in Wines

Novel integrated flow-based steam distillation and titration system with spectrophotometric detection was developed for determination of volatile acidity in wines. Using the system, the distillation procedure was carried out in an automatic manner, starting with introducing into a heated steam distillation module a sample and subjecting it to steam distillation. Under selected conditions, all the analyte was transferred to the distillate; therefore, the system did not require calibration. The collected distillate and titrant were introduced into the next monosegments in varying proportions, in accordance with the developed titration procedure, and directed to the detection system to record the titration curve. The titration was stopped after reaching the end point of titration. Procedures for distillation and titration were developed and verified separately by distillation of acetic acid, acetic acid in the presence of tartaric acid as well as acetic acid, tartaric acid, and titratable acidity, with precision (relative standard deviation) and accuracy (relative error) for both procedures lower than 6.9 and 5.6%, respectively. The developed steam distillation and titration systems were used to determine volatile acidity in samples of white and rosé wines separately and as the integrated steam distillation and titration system, both with precision lower than 9.4% and accuracy better than 6.7%.     

A new radiometric titration method based on separation by means of ion exchange,I

A new radiometric titration procedure is proposed, which is based on phase separation by means of an ion exchanger in the solution. The method can be applied in both complexometry and oxidimetry. A mathematical expression has been derived for the titration curves in both cases. In complexometry, a straight line is possible depending on the concentration, the mass-distribution coefficient and the complex constant, while the titration curve in oxidimetry should always be a straight line.     

Use of Surfactant-Stabilized Emulsions for the Alkalimetric Determination of Indometacin

The proton-donor properties of 1-(p-chlorobenzoyl)-5-methoxy-2-methylindole-3-acetic acid (indometacin) were studied in emulsions based on different surfactants and their mixtures. A procedure for the alkalimetric titration of indometacin with detecting the titration end-point in the presence of Cresol Red was developed using an emulsion based on dodecylpyridinium chloride. The conditions for determining indometacin in medicinal forms by pH-metric titration were selected.     

Spectrophotometric extracave titrations-VII Titrations with di-2-naphthylthiocarbazone

An investigation of the possibilities of the use of di-2-naphthylthiocarbazone as titrant in spectrophotometric extractive titrations has been undertaken. A selective procedure for successive titration of silver in an ammoniacal medium has been developed and applied to the analysis of germanium dioxide. It has been established that the consecutive titration of mercury and zinc in the microgram range is possible. Because of low selectivity of this titration, a separation of mercury and zinc from other ions is necessary.     

Coulometry applied to gas-phase chromatograpy

It has been found that coulometry is an excellent procedure for identification and quantitative determination of the components of an organic mixture, separated by vapor-phase chromatography. A millicoulometer is described which can be used either for manual or automatic titration. The eluted components are absorbed in a suitable solution where they are continuously titrated by an electrolytically generated reagent. Photometric, amperometric and potentiometric end-points may be used for the titration of compounds with an active functional group such as volatile acids, bases, mercaptans and aldehydes. The procedure can be extended to all organic vapors by burning them at the end of the column and converting them into carbon dioxide which can be coulometrically titrated.     

Estimation of uncertainty in p<Emphasis Type="Italic">K</Emphasis><Subscript>a</Subscript> values determined by potentiometric titration

A procedure is presented for estimation of uncertainty in measurement of the pK(a) of a weak acid by potentiometric titration. The procedure is based on the ISO GUM. The core of the procedure is a mathematical model that involves 40 input parameters. A novel approach is used for taking into account the purity of the acid, the impurities are not treated as inert compounds only, their possible acidic dissociation is also taken into account. Application to an example of practical pK(a) determination is presented. Altogether 67 different sources of uncertainty are identified and quantified within the example. The relative importance of different uncertainty sources is discussed. The most important source of uncertainty (with the experimental set-up of the example) is the uncertainty of pH measurement followed by the accuracy of the burette and the uncertainty of weighing. The procedure gives uncertainty separately for each point of the titration curve. The uncertainty depends on the amount of titrant added, being lowest in the central part of the titration curve. The possibilities of reducing the uncertainty and interpreting the drift of the pK(a) values obtained from the same curve are discussed.     

Digital image-based titrations

The exploitation of digital images obtained from a CCD camera (WebCam) as a novel instrumental detection technique for titration is proposed for the first time. Named of digital image-based (DIB) titration, it also requires, as a traditional titration (for example, spectrophotometric, potentiometric, conductimetric), a discontinuity in titration curves where there is an end point, which is associated to the chemical equivalence condition. The monitored signal in the DIB titration is a RGB-based value that is calculated, for each digital image, by using a proposed procedure based on the red, green, and blue colour system. The DIB titration was applied to determine HCl and H₃PO₄ in aqueous solutions and total alkalinity in mineral and tap waters. Its results were compared to the spectrophotometric (SPEC) titration and, by applying the paired t-test, no statistic difference between the results of both methods was verified at the 95% confidence level. Identical standard deviations were obtained by both titrations in the determinations of HCl and H₃PO₄, with a slightly better precision for DIB titration in the determinations of total alkalinity. The DIB titration shows to be an efficient and promising tool for quantitative chemical analysis and, as it employs an inexpensive device (WebCam) as analytical detector, it offers an economically viable alternative to titrations that need instrumental detection.     

Simultaneous determination of equivalence volumes and acid dissociation constants from potentiometric titration data

New iterative methods for analysis of potentiometric titration data of (a) mixtures of weak monoprotic acids with their conjugate bases, (b) solutions of polyprotic (di- and triprotic) acids, and (c) mixtures of two diprotic acids are presented. These methods, using data exclusively resulting from the acidic region of the titration curve permits the accurate determination of the analytical concentration of one or more acids even if the titration is stopped well before the end point of the titration. For the titration of a solution containing a conjugate acid/base pair, the proposed procedure enables the extraction of the initial composition of the mixture, as well as the dissociation constant of the concerned acid. Thus, it is possible by this type of analysis to distinguish whether a weak acid has been contaminated by a strong base and define the extent of the contamination. On the other hand, for the titration of polyprotic acids, the proposed approach enables the extraction of the accurate values of the equivalence volume and the dissociation constants K(i) even when the ionization stages overlap. Finally, for the titration of a mixture of two diprotic acids the proposed procedure enables the determination of the composition of the mixture even if the sum of the concentrations of the acids is not known. This method can be used in the analysis of solutions containing two diastereoisomeric forms of a weak diprotic acid. The test of the proposed procedures by means of ideal and Monte Carlo simulated data revealed that these methods are fairly applicable even when the titration data are considerably obscured by 'noise' or contain an important systematic error. The proposed procedures were also successfully applied to experimental titration data.     

A collaborative study of four methods of assay of benzylpenicillin

The assay of benzylpenicillin by iodimetric titration, spectrophotometry with a mercury(II) chloride—imidazole reagent, titration with mercury(II) nitrate in acetate buffer solution, and titration with mercury(II) perchlorate in aqueous pyridine solution, was examined in four laboratories. The first two methods were applied to two samples (the third one being the reference sample), the mercury(II) nitrate titration to three, and the mercury(II) perchlorate method to two samples. The four methods gave very similar results, but the purity obtained with the mercury(II) perchlorate method was slightly lower, and this procedure is less desirable because pyridine is used as solvent. There were no great differences in the relative standard deviations of the four methods. The titration with mercury(II) nitrate is preferred because it is an absolute method.     

The coulometric titration of bromate with cuprous copper

A coulometric procedure has been developed by which 18 to 240 μg quantities of bromate may be determined to within 0.3 μg. The bromate is allowed to react with bromide in an acid solution and electrolytically generated cuprous copper is used for the titration. A dual platinum electrode indicator system is used in an amperometric end-point procedure     

Determination of hexafluoropropan-2,2-diol in its binary mixtures with water

A visual titration method for the determination of hexafluoropropan-2,2-diol (HFPD) in HFPD-water mixtures is suggested. The procedure involves the titration of the weakly acidic HFPD with sodium methoxide, using dimethylformamide or ethanol as solvent and thymol blue as indicator. The results are in good agreement with the ones obtained by potentiometric titration in water.     

A new radiometric titration method based on separation by means of ion exchange

The determination of zinc with EDTA is chosen as an example for the earlier suggested new radio-complexometric titration procedure, in which phase separation is achieved by means of a strongly basic anion exchanger in the solution. Concentrations of zinc solutions down to 10⁻⁶ M have been determined. The reverse titration,viz. of EDTA with zinc solution, which can be used as back-titration in complexometry, is also possible. However, theoretical relations for this latter type of titration are not simple.     

Sequential potentiometric microdetermination of chloride and phosphate and its application to the determination of phosphorus and chlorine in organic compounds

Orthophosphate has been determined at the micro level in the presence of chloride by argentimetric potentiometric titration. Chloride is titrated first, at pH 3 in water-propan-2-ol (1:1 v/v), and phosphate in the same solution, buffered at pH 8.5-9.0. Under these conditions, the titration error from partial co-precipitation of silver oxide near the equivalence point is minimized. A procedure for performing the titration with an automatic apparatus is described. The method has been applied to the determination of phosphorus and chlorine in the same organic compound after mineralization by the Sch?niger method.     

Differential electrolytic potentiometric determination of some amino acids in dosage forms

The application of direct-current differential electrolytic potentiometry to the nonaqueous titration of amino acids was investigated. The basic character of amino acids in acetic acid was enhanced to permit their direct titration with perchloric acid. A pair of antimony electrodes was used as an indicating system. The shapes of the titration curves obtained were almost symmetrical with sharp peaks. The optimum current density for those titrations was found to be 1-2 microA/cm2. The procedure was applied successfully to the determination of certain amino acids in drug formulations, and the results were favorably compared statistically with those obtained by official methods.