Flow injection titration-linear or logarithmic

A simple and rapid Continuous Flow Injection Titration method utilizing a pretitration step was developed to automate the assay of high sulfuric acid concentrations over a narrow range in an oil refinery stream. A Coulometric Flow Injection Titration method was developed to perform Karl Fisher titration. Multiple functions of the mixing chamber in these FIA titrations such as for pretitration dilution, and reduction of viscosity are discussed. The cell also serves as the detector. Appropriate combining of these functions allows FIA titrations to become a powerful tool in automating routine assays.     

平头pH电极-流动注射联用技术快速滴定食醋中醋酸的方法研究

采用一种具有平头结构的pH电极作为流动注射分析(FIA)的检测器,构建了流动注射自动化酸度滴定系统.优化了样品进样量、流速、载液浓度和反应管长度等参数.用NaOH溶液作为载液,在4.639×10-4～0.212 mol·L-1范围内醋酸浓度的对数与FIA峰的峰面积成正比,该方法的相对标准偏差(RSD)小于0.5%.采用...     

Bromine number determination by coulometric flow-injection titration

The bromine number, the number of grams of bromine which react with 100 grams of a substance under given conditions, is a widely used parameter in the chemical and petroleum industries. A method of performing the bromine number determination by coulometric flow-injection titration, using both sequential injection with sinusoidal flow and single zone techniques, is described. Titrations of olefins, known interfering compounds, and petroleum distillates were performed and compared with the results of conventional bromine number titrations. Analyses yielded a relative standard deviation of 2%. Results compared favorably with those obtained by the conventional method for both pure (97%) olefins and petroleum distillates. The method was found to be insensitive to interference from nitrogen compounds. The CFIT technique combines the advantages of coulometric titrations: controlled generation of reagent, avoidance of reagent standardization requirements and reagent storage and stability problems; with the advantages of FIA: small volume requirements which reduce cost and waste, controllable dilution through flow programming, toxic materials contained within a closed environment, and the capability of being automated.     

Titrimetric methods for the determination of surface and total charge of functionalized nanofibrillated/microfibrillated cellulose (NFC/MFC)

Total and surface charge of three different carboxymethylated nanofibrillated/microfibrillated cellulose (NFC/MFC) samples were investigated by using titrimetric methods (conductometric and polyelectrolyte (PE) titrations). Conductometric titration was found to be suitable method for the NFC total charge measurements when the back titration with HCl was applied. Surface charge measurements of NFC/MFC were conducted by using both indirect and direct PE titrations. The direct PE titration was found to be a more suitable method for the surface charge determination of NFC/MFC whereas the indirect PE titration produced too high surface charge values. This is presumably due to kinetically locked polyelectrolyte conformations on the NFC/MFC surfaces or entrapment of residual polymer after adsorption onto the NFC/MFC gel network. Finally, NFC was propargyl-functionalized and the changes in surface and total charge were successfully monitored and compared to those of propargyl-functionalized pulp. A good correlation between the titrimetric methods and elemental analysis was observed.     

Determination of Na(2)O from sodium aluminate NaAlO(2)

The aim of the work was to find a suitable method and conditions for determining Na(2)O wt.% from NaAlO(2). Problems were encountered while titrating NaAlO(2) with hydrochloric acid. The problematic area was the pH range 4-10 where aluminum precipitates as hydroxides. The different species of the aluminate solution were determined using potentiometric and complexometric titrations. The equivalent point of the potentiometric titration was detected using Gran's plotting method. Precipitation of aluminum hydroxides did not interfere with titrations, because in potentiometric titrations the pH value was over 10 and in complexometric titrations the pH was 4. The results were accurate and determinations were easy to carry out. Sodium was also determined by DCP-AES.     

Acid-base titrations by stepwise addition of equal volumes of titrant with special reference to automatic titrations-IV Photometric titration of an acid

In Part I of this series, evaluation methods for potentiometric titrations of acids performed by stepwise addition of titrant were introduced. These methods are non-approximative and may therefore in principle be applied to titrations of acids of any strength. This paper demonstrates that photometric titrations performed by stepwise addition of titrant may also be evaluated by the proposed methods. The photometric method is compared with the potentiometric method of monitoring the course of a titration.     

Logarithmic diagrams as an aid in complexometric titrations where 1:2 or 2:1 as well as 1:1 metal-ligand complexes are regarded as principal species

Logarithmic diagrams have earlier been used for theoretical treatment of complexometric titrations where only the 1:1 complex is formed in the main reaction between a metal ion M and a ligand L. This approach has now been extended to include titrations where 1:2 and 2:1 complexes are also formed. Four different types of diagram can be drawn. These diagrams can be used to determine pM (or pL) at the equivalence point, the titration ratio at different pM (or pL) values and the titration error. One of these diagrams is easy to construct and use. The method also has the advantage that it can directly indicate whether the titration is best performed with 1:1 or 2:1 (1:2) stoichiometry. Two typical examples, namely the titration of a manganese solution with triethylenetetraminehexa-acetic acid and of a copper solution with pyridine-2,6-dicarboxylic acid, are discussed. The two titrations proceed with the formation of the complexes Mn(2)L (2: 1) and CuL(2) (1:2) respectively, in addition to the 1:1 complex in each instance.     

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.     

Some observations on catalytic conductometric titrations

Conductometric and high-frequency conductometric methods for the determination of the endpoint of catalytic titrations were developed. Titrations of sodium acetate were made in a mixture of acetic anhydride and acetic acid (7:3–11:3) which was 0.05–0.1 mol dm⁻³ in sodium perchlorate. Integral and derivative titration curves were recorded in both coulometric and volumetric titrations. Different acylation reactions, as well as dehydration of formic acid, were used as the indicator reactions. The optimal conditions of determination—choice of volume ratio of acetic anhydride to acetic acid, rate of the titrating reagent addition, concentration of sodium perchlorate, and concentration of several alcohols, water, and formic acid as components of the indicator reactions—were determined. Using the catalytic conductometric method, amounts of 0.04–11 mg of sodium acetate were determined with a relative standard deviation of less than 0.8 and 1.6% in volumetric and coulometric addition, respectively. Using the catalytic high-frequency conductometric method, amounts of 1–11 mg of sodium acetate were determined with relative standard deviation less than 0.5% (volumetrically) or less than 1.4% (coulometrically). The obtained results were compared with those of potentiometric and catalytic thermometric titrations.     

零流电位法在酸碱滴定中的应用研究

探讨了零流电位法在酸碱滴定中的检测原理及应用,通过考察强碱滴定弱酸、强碱滴定强酸、强酸滴定弱碱以及强酸滴定强碱四种滴定体系,探明了零流电位法在酸碱滴定中的适用性。通过氢氧化钠滴定醋酸对本方法进行评价,实验结果表明:本法的相对误差为-0.4%,同一根电极的滴定值的相对标准偏差(RSD)为0.4%(n=5),同一根电极五天滴定值的RSD为0.6%,五根电极滴定值的RSD为0.5%。本方法具有较高的准确性、稳定性和重现性。     

Computer controlled titration with piston burette or peristaltic pump – a comparison

The advantages and problems of the use of piston burettes and peristaltic pumps for dosage of titrant solutions in automatic titrations are shown. For comparison, only the dosing devices were exchanged and all other components and conditions remained unchanged. The results of continuous acid base titration show good agreement and comparable reproducibility. Potentiometric sensors (glass electrodes) with different equilibration behaviour influence the results. The capability of such electrodes was tested. Conductometric measurements allow a much faster detection because there is no equilibration of electrodes. Piston burettes should be used for titration with very high precision, titration with organic solvents and slow titrations. Peristaltic pumps seem to be more suitable for continuous titrations and long time operation without service.     

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.     

Potentiometric study of reaction between periodate and iodide as their tetrabutylammonium salts in chloroform. Application to the determination of iodide and potentiometric detection of end points in acid-base titrations in chloroform

A potentiometric method for the titration of tetrabutylammonium iodide (TBAI) in chloroform using tetrabutylammonium periodate (TBAPI) as a strong and suitable oxidizing reagent is described. The potentiometric conditions were optimized and the equilibrium constants of the reactions occurring during the titration were determined. The method was used for the determination of iodide both in chloroform and aqueous solutions after extraction into chloroform as ion-association with tetraphenylarsonium. The reaction between TBAPI and TBAI was also used as acid indicator for the potentiometric detection of end points of acid-base titrations in chloroform.     

Comparison of three electrochemical end-point detection methods to assay potassium dichromate by coulometric titration

Coulometric titrations with three electrochemical end-point detection methods were performed to assay potassium dichromate as a standard for oxidation–reduction titration. The assay as an oxidizing agent was carried out with ferrous ions produced by electrolytically reducing ferric ions. Three end-point detection methods were employed and compared with each other: constant potential amperometry, potentiometry, and constant voltage biamperometry (a dead-stop method). The last one was found to provide high accuracy in the coulometric titration of potassium dichromate. Solution form samples were also measured to confirm the possible existence of chromium(III) in potassium dichromate by both coulometric titration and ion-exchange chromatography with inductively coupled plasma time-of-flight mass spectrometry.     

Thermometric titration in investigation of the formation of polyanions of molybdenum(VI), tungsten(VI), vanadium(V), and chromium (VI)-I: comparison of thermometric and potentiometric titration curves

A new twin-cell thermometric titrator has been devised and used for thermometric titration of solutions of sodium molybdate, sodium tungstate, sodium orthovanadate, ammonium metavanadate, and potassium chromate with perchloric acid. The thermometric titration curves were compared with corresponding pH-titration curves for elucidation of the reactions occurring in the titrations. Thermometric titrimetric methods have been developed for the determination of tungsten, vanadium and chromium.     

Direct determination of thiol pKa by isothermal titration microcalorimetry

Knowledge of the acid dissociation constant (pKa) of a molecule is a critical step toward understanding its structure and reactivity. Current methods for pKa measurement, including electrochemical, spectroscopic, and spectrophotometric titrations, have proven to be useful but also have significant limitations. To overcome these limitations, we report the use of isothermal titration calorimetry (ITC) as a new method for pKa determination. We demonstrate by the measurement of the pKa values for free cysteine, glutathione, and a cysteine residue in a protein that this method is rapid and accurate.     

Titration of 6-aminopenicillanic acid with mercury (II) solution.

A simple, absolute method for the determination of 6-aminopenicillanic acid (6-APA) is described. The method involves two titrations with mercury(II) nitrate solution at pH 4.8, the first on an untreated solution and the second on a solution which has been acetylated, alkali-hydrolysed, and neutralized. The first titration accounts for the degradation products of 6-APA; the second titration gives the sum of these products and the intact 6-APA in the sample. The method is rapid and accurate.     

Determination of fiber charge components of Lo-solids unbleached kraft pulps

Four different titration methods for measurement of fiber charge were used in this study. Each method gave different fiber charge values depending on the acidity of the end point and the interaction between the fiber chemical components and the titrant. Also, the interactions between the ionizable groups on the fiber had significant effects on the interpretation of these results. The conductometric titrations showed trends similar to the results obtained from the potentiometric titration. The conductometric titrations with NaOH produced higher fiber charge values, higher than the titrations with NaHCO(3). The differences between the results obtained from the potentiometric and polyelectrolyte titrations, which were associated with the dissolved fiber components during the delignification, were linearly related to the Kappa number of pulps. The positive intercept of this linear relationship indicated that the kraft pulping process not only removed the ionizable groups associated with the dissolved components, but at the same time provided conditions to form new ionizable groups in the fibers. The polyelectrolyte titration results indicated that the lignin content in the fibers did not affect the fiber surface charge. Data extracted from the FTIR spectra of protonated fibers were highly correlated with the fiber charge values obtained from the conductometric titration with NaOH.     

Möglichkeiten für die Automatisierung komplexometrischer Titrationen

In the automatation of complexometric titration such indication procedures are of special interest which show a distinct electrical signal at the titration endpoint. Although potentiometric and amperometric methods are well suited for this purpose their range of application is either not wide enough or the expenditure on measuring devices is too high. Voltametric indication, however, does not involve these drawbacks. This method allows the indication of practically all complexometric titrations with great accuracy in either acid, neutral, ammoniacal or alkaline solutions, including backtitration and substitution titration, independent of the chelating reagent used. Therefore it is very useful for the purpose in question. Using the combination polarized noble-metal cathode/polarized noble-metal anode coated with a thin film of oxides of non-noble-metals (such as Bi, Tl, and Mn) is of particular advantage in so far as the titration of alkaline earths may also be indicated by the said method. The conditions under which such anodes are prepared are described; their efficiency is demonstrated.     

Rapid Automatic Determination of Calcium and Magnesium in Aqueous Solutions by FIA Using Potentiometric Detection

A pH‐sensitive detector for flow‐through potentiometry based on a graphite/quinhydrone/silicone composite electrode was applied to determine calcium and magnesium in aqueous solutions. The determinations are performed by FIA titrations with EDTA as the carrier solution. The method was applied to the analysis of mineral water, drinking water, and river water. The results were compared with those obtained by batch complexometric titration. The proposed new method is suitable for the simple, rapid and automated determination of water hardness in small sample volumes of aqueous solutions. The detection limit for both ions is about 1×10^?5 mol L^?1, the standard deviation is less than 2%. The sampling frequency is 60 determinations per hour.