A turbidimetric method for colloid titrations

Positive colloid solutions can be titrated with the polyanion potassium polyvinylsulfate with toluidine blue as indicator, but negative colloid solutions must be treated with an excess of the polycation polydiallyldimethylammonium chloride which is backtitrated with potassium polyvinylsulfate. By turbidimetry however, positive or negative colloid solutions can be directly titrated with, respectively, the polyanionic or polycationic titrant. Two methods, the construction and differential methods, can be used. The latter method is particularly useful when a flocculent precipitate appears during the titration.     

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.     

2-methoxyethanol as a solvent for conductometric acid-base titrations

Conductometric titrations of a series of organic acids in 2-methoxyethanol were performed with 1,3-diphenylguanidine (DPG) as titrant. For benzoic, p-chlorobenzoic and picric acids, phenylphenol and barbital, excellent recoveries were obtained from well-defined conductance vs. volume plots. Results for the dicarboxylic phthalic and adipic acids were also good. However, the titration curves for the difunctional salicylic and p-hydroxybenzoic acids were not clearly defined. The results are discussed and compared with cnductometric titrations of acids in other non-aqueous solvents. Several determinations of electrolyte conductance as a function of concentration revealed that, as expected, the selected substances are weak electrolytes in methoxyethanol.     

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.     

Calorimetric and conductometric titrations of nanostructures of water molecules in iteratively filtered water

This work continue the study of the physico-chemical properties of samples of pure, twice distilled water, when subject to a procedure of iterative filtrations through Pyrex glass filters (Büchner funnels). After the filtrations, electrical conductivity and heat of mixing with NaOH and HCl solutions increase. The hypothesis is that the iterative filtration procedure, that involves a flux of energy and material in an open system, is able to induce the formation of “dissipative structures” or nanostructures of water molecules (WNS). Water exhibits an extraordinary auto-organization potentiality triggered by several kinds of perturbations, including mechanical ones. We measured the heats of mixing of acid or basic solutions with such iterated filtered waters (IFW) and their electrical conductivity, comparing with the analogous heats of mixing, electrical conductivity of the solvent. We found some relevant exothermic excess heats of mixing and higher conductivity than those of the untreated solvent. The heats of mixing and electrical conductivity of IFW show a good correlation, underlining a single cause for the behavior of the samples.     

A new method for simultaneous estimation of micellization parameters from conductometric data

A simple method for determination of the counterion binding parameter (alpha) and aggregation number (N) from conductivity data is proposed. The method is based on fitting the values of the first derivative of conductivity (kappa) versus total surfactant concentration (c(t)) function according to the equation derived from the mass action model (MAM) by using different conductivity models. Sodium dodecylsulphate (SDS) and dodecyltrimethylammonium bromide (DTAB) were chosen for validation of the proposed method. It was shown that the method gives a fairly accurate values for micellisation parameters of SDS (N=51-64, alpha=0.74-0.75) and DTAB (N=56-62, alpha=0.77-0.79), both in good agreement with the literature data. In addition, application of the proposed method does not require the value of the critical micelle concentration (cmc).     

The use of benzidine dihydrochloride for sulfate determinations : A direct conductometric titration method

Sulfate in small quantities may be determined by direct conductometric titration with standard benzidine dihydrochloride solution within a maximum error of less than one percent. Optimum conditions have been determined for the procedure.     

A simple and precise conductometric method for the determination of losartan in pharmaceutical products

Losartan is an antihypertensive agent that lost its patent protection in 2010, and, consequently, it has been available in generic form. The latter motivated the search for a rapid and precise alternative method. Here, a simple conductometric titration in aqueous medium is described for the losartan analysis in pharmaceutical formulations. The first step of the titration occurs with the protonation of losartan producing a white precipitate and resulting in a slow increase in conductivity. When the protonation stage is complete, a sharp increase in conductivity occurs which was determined to be due to the presence of excess of acid. The titrimetric method was applied to the determination of losartan in pharmaceutical products and the results are comparable with values obtained using a chromatographic method recommended by the United States Pharmacopoeia. The relative standard deviation for successive measurements of a 125 mg L^?1 (2.71×10^?4 mol L^?1) losartan solution was approximately 2%. Recovery study in tablet samples ranged between 99 and 102.4%. The procedure is fast, simple, and represents an attractive alternative for losartan quantification in routine analysis. In addition, it avoids organic solvents, minimizes the risk of exposure to the operator, and the waste treatment is easier compared to classical chromatographic methods.      

A modified gran method for determination of equivalence points in potentiometric precipitation titrations

Gran's method is frequently applied in potentiometric titration to obtain a more precise estimate of the equivalence point, particularly when the analyte concentration is too low to give well defined end-points. With precipitation reactions, however, when the analyte concentration is comparable to the solubility of the precipitate, even the use of Gran's method will not avoid significant errors. A correction term is introduced and a computer program outlined to overcome this problem. Titrations of 10^-4 M chloride are used for illustration.     

A new sensor for thermometric titrations

A new thermometric sensor, which is a transistor (OC71), has been introduced to follow thermometric titrations successfully to clear end points. The sensor was suitable in both normal and differential modes of titration. It is possible to titrate down to 1.32 μmol of HCl and 26.4 μmol of H₃BO₃in a final 20 ml solution with accuracy and precision of 1%, 2.2% and 1.4%, 2.2%, respectively. The sensor, in association with a pH glass electrode, was used for the determination of pK values of some well established weak acids such as, acetic acid (4.77), phosphoric acid (pK₁ = 2.18, pK₂ = 7.20 and pK₃ = 12.32) as well as for a very weak acid of uncertain pK values H₃BO₃ (pK₁ = 9.20, pK₂ = 12.7 and pK₃ = 13.80). The sensor was also examined for kinetic catalytic determination of iron(III) in water, milk and pharmaceuticals.     

A conductometric device for monitoring of enzyme-catalyzed reactions

A new conductometric device is described for measurement of conductance changes during enzyme-catalyzed reactions. The use of platinum resistances inside the cell allows temperature regulation to be obtained without circulating water. Solutions are introduced and removed from the cell with a peristaltic pump. The device is evaluated by assaying serum urea concentrations down to 40 nM. The results correlate well with a spectrophotometric method based on biacetylmonoxime (r=0.997).     

A potential high-throughput method for the determination of lipase activity by potentiometric flow injection titrations

Potentiometric FIA titrations were performed to determine enzyme activities of lipase type B from Candida antarctica, CAL-B. Two substrates, triacetin and tributyrin were hydrolyzed in phosphate buffer solutions, and the concentration change of the base component of the buffer was titrated in a carrier solution containing hydrochloric acid and potassium chloride. The system was calibrated with butyric acid and acetic acid, respectively. FIA titration peaks were evaluated with respect to peak height and peak area. Butyric acid and acetic acid could be titrated in the buffer solution from 3 × 10⁻³ mol L⁻¹ to 0.1 mol L⁻¹. The detection limit of enzyme activity was determined to be 0.07 U mL⁻¹ (15 min reaction time) and the minimum activity was calculated to be 0.035 units corresponding to 35 nmol min⁻¹. The specific activities of lipase B for the hydrolysis of tributyrin and triacetin were determined as 16 ± 2 U mg⁻¹ and 2 ± 0.2 U mg⁻¹ (per mg commercial lipase preparation), respectively.     

A novel power-controlling approach for integrated,conductometric gas sensors

An original power controlling driving/reading circuit for Porous Silicon JFET (PSJFET) gas sensors is presented. The PSJFET is an integrated p-channel JFET with two independent gates: a meso-structured PS layer, acting as a sensing, floating gate, which modulates the JFET current upon adsorption/desorption of specific analytes, and a high-impedance electric gate, which allows the JFET current tuning independently from analytes in the environment. The circuit exploits the independence of the sensing and electrical gate terminals to set/control the sensor power-dissipation, which is kept almost constant independently from adsorption/desorption-induced effects, while simultaneously carrying out a current-voltage conversion. For such a purpose, a negative feedback loop is used to modulate the PSJFET electric gate voltage, which becomes the output signal, while keeping constant the source-drain sensor current and, hence, the power dissipation. The proposed approach is validated by performing time-resolved measurements on PSJFET sensors under different NO₂ concentrations (100ppb, 300ppb, 500ppb), at room temperature.     

A continuous reading vacuum tube voltmeter for electrometric titrations

A simple, continuous-reading, mains-operated, vacuum-tube voltmeter for electrometric titrations is described, using two tubes EBC₃ in a Wheatstone-bridge circuit.     

A graphical approach to redox titrations

Summary A method for drawing a logarithmic diagram which gives a correct representation of the equilibrium concentrations of the various species taking part in a redox titration is described. The use of this kind of diagrams for evaluating the titration error and for calculating the titration curve is illustrated. The symmetry properties of titration curves and the linearity range of Gran plots are also discussed on the basis of the logarithmic diagrams.

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Graphische Behandlung von Redox-Titrationen

Zusammenfassung Ein Verfahren wird beschrieben zur Aufstellung eines logarithmischen Diagramms, das eine korrekte Darstellung der Gleichgewichtskonzentrationen der verschiedenen Teilnehmer an einer Redoxtitration bietet. Der Gebrauch eines solchen Diagramms zur Auswertung des Titrationsfehlers und zur Berechnung der Titrationskurve wird gezeigt. Aufgrund der logarithmischen Diagramme werden auch die Symmetrieeigenschaften von Titrationskurven und der Linearitätsbereich von Gran-Diagrammen diskutiert.

     

Photometric titrations

Within the last few years, photometric titration has become an increasingly important analytical method. The principles of the method are discussed and sources of error briefly mentioned. A comprehensive review of recent applications of the technique is given.