Determination of lead(II) by argentimetry

A titrimetric method for determination of lead(II), based on the reaction between plumbite and silver ions, is described. Sodium hydroxide solution is added to the sample until the precipitate of lead hydroxide has redissolved. The solution is then made 0.025M in sodium chloride and titrated with silver nitrate. The titration is monitored with a silver electrode. An error smaller than 0.5% has been obtained for 0.05M lead (II).     

Studies on the mode of action of fajans' adsorption indicators

The mode of action of Fajans' adsorption indicators in the case of eosin with silver chloride and rhodizonate with barium sulphate is studied. It is established that because of the adsorption of the silver or barium ion the solubility product of silver eosinate and barium rhodizonate at the surface of the corresponding precipitate is reached sooner than it would be, calculated on the basis of the indicator concentration in the solution. The precipitation of silver eosinate or barium rhodizonate at the surface of the precipitate is influenced by factors affecting their solubility.     

Indirect potentiometric titration of sulphamethoxazole in the presence of trimethoprim in co-trimazole tablets using copper based mercury film electrode

A simple and rapid indirect potentiometric titration of sulphamethoxazole in the presence of trimethoprim contained in co-trimazole tablets is described. The method is based on the formation of a complex of sulphamethoxazole with a known excess of silver ions and the titration of unreacted silver ion potentiometrically using an inexpensive lab-made copper based mercury film electrode (CBMFE). The titration conditions have been optimized for the determination of 1.0-10.0 mg of sulphamethoxazole in pure and dosage forms. The precision and accuracy of the method have been assessed by the application of lack of fit test and other statistical methods. Overall mean recovery and relative standard deviations obtained were 99.88% and 1.32% (n=7) respectively. No interference was caused by other excipients present in pharmaceutical dosage forms. The application of this method for sulphamethoxazole assay in the presence of trimethoprim in tablets was validated by the comparison of results obtained by the proposed method with that of the British Pharmacopoeia (BP) method using F- and t-statistical tests of significance.     

Determination coulometrique d'alcaloides et de sels de bases organiques apres precipitation sous forme de tetraphenylborates

A coulometric microdetermination of salts of certain organic bases and alkaloids is described, based on precipitation as the tetraphenylborates and the coulometric determination of the tetraphenylborate content of the precipitate with electrogenerated silver ion. Eleven compounds were determined with satisfactory accuracy.     

Indirect complexometric determination of chromate

Chromate is determined indirectly, by precipitation as silver chromate, dissolution of the precipitate in potassium tetracyanonickelate, and titration of the liberated nickel with EDTA, with Murexide as indicator.     

Silver(I) ion-selective membrane based on Schiff base-p-tert-butylcalix[4]arene

A PVC membrane electrode for silver(I) ion based on Schiff base-p-tert-butylcalix[4]arene is reported. The electrode works well over a wide range of concentration (1.0 x 10(-5)-1.0 x 10(-1) mol dm-3) with a Nernstian slope of 59.7 mV per decade. The electrode shows a fast response time of 20 s and operates in the pH range 1.0-5.6. The sensor can be used for more than 6 months without any divergence in the potential. The selectivity of the electrode was studied and it was found that the electrode exhibits good selectivity for silver ion over some alkali, alkaline earth and transition metal ions. The silver ion-selective electrode was used as an indicator electrode for the potentiometric titration of silver ion in solution using a standard solution of sodium chloride; a sharp potential change occurs at the end-point. The applicability of the sensor to silver(I) ion measurement in water samples spiked with silver nitrate is illustrated.     

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.     

Application of silver/sulfide ion-selective electrode for the determination of aliphatic primary and secondary amines

Aliphatic primary and secondary amines were determined utilizing their reaction with carbon disulfide. A potentiometric titration of the formed dithiocarbamates (I) with silver nitrate using a silver/sulfide ion-selective electrode was carried out. The effects of solvent, base, temperature and reaction time were investigated. The optimum conditions for a quantitative formation of (I) requires a minimal amount of 1,4-dioxane, 2 drops of 0.2% sodium hydroxide solution, excess carbon disulfide to stand at room temperature for 15 min. The titration requires prior evaporation of the unreacted carbon disulfide at 46 ° C. An average recovery of 98.5% with a standard deviation of 0.69 was obtained for the analyzed amines.     

La détermination indirecte du tungsténe dans les minerais par voie complexométrique

The determination of tungsten by gravimetric methods is time-consuming and requires special precautions. A simple and rapid method is described for the indirect determination of tungsten in minerals by means of complexometric titration.The separation of tungsten (in the form of sodium, tungstate) is obtained by precipitation of this soluble salt by means of calcium chloride. The precipitate of calcium tungstate is filtered and decomposed into calcium chloride and tungstic acid (insoluble) by treating with concentrated hydrochloric acid.The filtrate is made alkaline and serves for the titration with a 0.1M solution of Complexon III. One ml of this solution corresponds to 23.1867 mg of WO₃. This determination of Lungyten takes 3 to 4 hours.     

Silver(I)-selective coated-wire electrode based on an octahydroxycalix[4]arene derivative.

The performance of octahydroxycalix[4]arene derivative used as a neutral carrier for silver polymeric membrane electrode was studied. The sensor gave a good Nernstian response of 58 +/- 1 mV per decade for silver ion in the activity range 3.3 x 10(-6) to 3.3 x 10(-2) M Ag+. The limit of detection reached 2.1 x 10(-6) M Ag+ and exhibited high selectivity for silver ion against the alkali, alkaline earth and transition metal ions. The sensor can be used in wide pH range from 1.5 to 6.5. The response time of the sensor is less than 20 s. The potentiometric sensor was used as the indicator electrode in the titration of Ag+ ions by sodium chloride solution.     

Microdetermination of phosphate with EDTA

An indirect microdetermination of phosphate via EDTA titration is described, which can be applied to minerals, soils, fertilizers, biological samples, drugs and organo-phosphorus compounds. The method is based on the precipitation of phosphate as the very insoluble silver orthophosphate (K_sp = 1.3 × 10^?20), dissolution of this precipitate in a solution of potassium cyanonickelate and titration of the nickel displaced by silver. The phosphate content is obtained indirectly by multiplying the number of ml of the titrant by a factor. The method takes about an hour after the phosphate is brought into solution. The accuracy is about 1% for samples containing 5–50 mg PO₄^3? and about 3–5% for samples with 100 to 5000 μg PO₄^3?.     

Enthalpies of reaction of calcium chloride and sodium oxalate in an aqueous NaCl solution

The heats of mixing of dilute aqueous solutions of calcium chloride and sodium oxalate with additions of 1–5 wt % NaCl at 298.15 K and the heats of dilution of calcium chloride solutions were measured. Increasing the sodium chloride content in a solution noticeably increases the time of precipitation of calcium oxalate. A fine precipitate of CaC₂O₄ formed in solutions containing 3 and 5 wt % NaCl is difficult to remove from the parts of a calorimeter cell. The enthalpies of precipitation of CaC₂O₄ depend slightly on the content of the “background electrolyte,” whereas the enthalpies of dilution, owing to ion association, significantly decrease in magnitude and become positive in a 5% NaCl solution. The “standard” enthalpy of precipitation in water, determined by extrapolation of the experimental values to the zero concentration of the background electrolyte, differs noticeably from the enthalpy of precipitation in water.     

Phase equilibria for salt-induced lysozyme precipitation: Effect of salt type and temperature

The salt-induced precipitation of lysozyme from aqueous solutions was studied through precipitation assays in which the equilibrium compositions of the coexisting phases were determined. Lysozyme precipitation experiments were carried out at 5, 15 and 25 °C and pH 7.0 with ammonium sulfate, sodium sulfate and sodium chloride as precipitating agents. In these experiments a complete separation of the coexisting phases (liquid and solid) could not be achieved. Nevertheless it was possible to determine the composition of the precipitate. The enzymatic activity of lysozyme in the supernatant phase as well as in the precipitate phase was also determined. The activity balance suggests that there is a relationship between the composition of the true precipitate and the total activity recovery.     

Potentiometric studies on organic compounds containing sulphur with a sulphide ion-selective membrane electrode

Phenylthiourea and N,N-diphenylthiourea can be determined in the concentration range 10¹–10^?3M by potentiometric titration with silver nitrate solution with a sulphide ion-selective membrane electrode. The influence of the alkali and acid concentration on the course of the reactions with the silver nitrate titrant was studied. When phenylthiourea is titrated in the presence of 0.1 M sodium hydroxide, silver sulphide is precipitated, and the phenylcyanamide formed simultaneously reacts further with silver nitrate to form a silver phenylcyanamide precipitate. When N,N-diphenylthiourea is titrated under similar conditions, silver sulphide is again formed, but no cyanamide-type compound can be formed owing to the presence of the second phenyl group. In 1 M sodium hydroxide both compounds studied react with two equivalents of silver to give silver sulphide and phenylurea or diphenylurea, respectively. In the presence of nitric acid both compounds react similarly with silver nitrate. Two molecules of the compounds react with one molecule of silver nitrate to give a white precipitate.     

New method for determining small concentrations of chloride ion

A new method has been devised for the determination of concentrations of chloride ion from approximately 10^-6 to 2·10^-4 M. The test solution is equilibrated with solid silver chloride, the silver ion concentration is determined by potentiometric titration with iodide ion, and the chloride concentration is calculated by the solubility product principle. Chloride concentrations near 10^-6 M can be determined with an accuracy of about ±5%, and at 10^-5 M the error is within ±0.5%. Chloride concentrations above 2-3· 10^-4 M cannot be accurately determined because of the formation of AgCl₂^-.     

Determination of the performance of glass electrodes in aqueous solutions in the physiological ph range and at the physiological sodium ion concentration

A method for testing glass electrodes in the physiological pH range (6.4–7.6) and at the physiological sodium ion concentration (0.15 mol l^-1), based on indirect comparison of potentials with the hydrogen gas electrode, is developed according to a scheme described earlier. The hydrogen ion sensitivity and the sodium ion error of a glass electrode can be determined with three different aqueous solutions of amine buffers and their hydrochlorides; two of these have different pH values and one also contains a sodium salt (at the higher pH value). A cell without a liquid/liquid junction, containing silver/silver chloride reference electrodes, is used at 37° C. The accuracy of both determinations is ±0.2 mV (±0.003 pH). The results for some commercial glass electrodes tested with this method are presented.     

Studies on adsorption indicators : p-ethoxychrysoidine as adsorption indicator

p-Ethoxychrysoidine is studied as adsorption indicator in the direct titration of silver with iodide, bromide, thiocyanate and chloride at pH 4–5. The explanation given by Schulek and Pungor for the colour changes has been modified in the light of compound formation on the surface of the precipitate. The silver compound of p-ethoxychrysoidine has been isolated ; its behaviour provides a suitable explanation for the colour changes as well as the pH changes in the titrations.     

The titration error in potentiometric precipitation titration

The titration error can be calculated with the aid of the value of the buffer index determined at the inflection point of the titration curve when a precipitation titration is followed with an ion-selective electrode. When the precipitate is not formed ideally in the titration (i.e., is not formed under equilibrium conditions) the titration error cannot be predicted from the values of the solubility product, nor can the values of the solubility product be calculated from titration data at the inflection point.     

Simple instrument for titrimetry without visual indicators. Gasometric titrations: Argentometry

Several argentometric determinations have been worked out to show that the gasometric titration method is applicable not only to acid-base and redox reactions, but also to precipitation and complex-formation reactions. The processes reported allow the direct and indirect determination of iodide and cyanide, as well as the direct titration of silver ion in soluble and slightly soluble silver salts.     

Comments on the potentiometric titration of halides including fluoride with a mixed titrant

An attempt was made to verify work reported by others on the potentiometric titration of halides including fluoride with a mixed titrant of silver nitrate and thorium nitrate. The platinum indicator electrode can indeed be used to monitor the titration of bromide and chloride. However, we could not verify the results reported for fluoride. There seems to be no theoretical basis on which to expect the platinum electrode to respond to changes in fluoride ion concentration.