Potentiometric End-point Detection Research Articles

Acid — base titrations of barbiturates in aqueous micellar Media

Some barbiturates have been determined in cationic micellar systems by acid-base titrimetry, using both visual and potentiometric end-point detection. The method is shown to be a convenient alternative for the direct accurate and precise assay of microgram amounts of barbiturates.

Determination of plutonium and uranium in the same aliquot by potentiometric titration

A potentiometric titration method was developed for the determination of plutonium and uranium in the same aliquot in nitric acid medium. Plutonium was first determined by oxidation to Pu/VI/ by fuming with conc. HClO4. Pu/VI/ formed was reduced to Pu/IV/ with known excess of Fe/II/ and the excess Fe/II/ was titrated with standard K2Cr2O7 to a potentiometric end point. Uranium in the same solution was determined by reduction to U/IV/ with Fe/II/ in conc. H3PO4 medium and titrating U/IV/ formed with standard K2Cr2O7 using the potentiometric end point detection technique. For the quantity of plutonium and uranium each in the range of 3–5 mg per aliquot a precision of ±0.2% and ±0.4%, respectively, was obtained.

A method for the determination of maleic anhydride content in copolymers

A simple and reliable non-aqueous direct titration method for the determination of anhydride content in maleic anhydride-vinyl acetate copolymers is described. The procedure involves reaction of the anhydride with a large excess of aniline followed by direct titration of the resulting monoacid with ethanolic NaOH using potentiometric or thymol blue end point detection. The method overcomes many of the disadvantages of previously published methods, and its application to other copolymers is considered.

Spectrophotometric determination of nonstoichiometry in hyperstoichiometric uranium dioxide

Uranium dioxide is widely used as a nuclear fuel and usually exists as hyperstoichiometric UO/sub 2+x/. In the described method UO/sub 2+x/ is dissolved in warm concentrated phosphoric acid saturated with sodium sulfate at room temperature to prevent the air oxidation of U(IV). The concentrations of U(VI) and U(IV) are directly determined by means of the absorbance of the two species at two specific wavelengths 420 and 665 nm, respectively. The results obtained are precise to +/- 0.002 O/U units and have been compared with those obtained from gravimetric titrimetry employing potentiometric end point detection. The O/U ratio determined by the two procedures agrees within 0.004 O/U units. The method has been employed to determine O/U ratio in near stoichiometric UO/sub 2/ (2.039) as well as in U/sub 3/O/sub 8/ (2.670). The developed spectrophotometric method is simple and fast and does not require inert atmosphere.

Coulometric titrations using computer-interfaced potentiometric endpoint detection

62. Bits and pieces, 25. A procedure for using a potentiometric endpoint detection system interfaced with a computer to facilitate endpoint detection.

Anodically generated cobalt(III) acetate as reagent for coulometric titrations in acetic acid

Conditions for the anodic generation of cobalt(III) acetate with high current efficiency in non-aqueous solutions of potassium acetate in acetic acid have been investigated. The presence of water or acetic anhydride in the anolyte diminishes the amount of the generated oxidant. The stability of the generated cobalt(III) acetate solution is decreased in the presence of water and at elevated temperatures. Procedures for coulometric titrations of reducing substances with cobalt(III) acetate, using the biamperometric or the potentiometric end point detection, are described.

Coulometric generation of hydrogen ions by oxidation of mercury in anhydrous acetone

The application of a mercury anode for the quantitative generation of H + ions in anhydrous acetone has been investigated. From the changes of anode potential with current density in 0.25 M sodium perehlorate in anhydrous acetone it has been established that in this solvent mercury is oxidized at a potential which is much more negative than the oxidation potentials of the bases to be titrated, the indicator used and the solvent. Protons generated in this way have been used for titration of some organic bases, with either visual or potentiometric end-point detection. The oxidation of mercury in anhydrous acetone and the reaction of mercury ions with acetone have been found to proceed with 100% current efficiency.

A Microprocessor Controlled Coulometric Titrator System For The Determination Of Chloride Ion

ABSTRACT A 6502 microprocessor based system has been developed for control, end point detection, and determination of elapsed electrolysis time for a constant current coulometer. The coulometer consists of operational amplifier controlled current source, differential potentiometric end point detection circuitry, and a KIM-1 microprocessor controlled timer/concentration level indicator. The differential potentiometric indicating electrode potential is compared with a user selected end point potential. When the preset end point potential is exceeded the electrolysis current is shut off automatically. The on-board 6530 interval timer is used to display either time in hundreths of a second or sample concentration directly. The system is applied to the determination of chloride ion in natural water samples. A detection limit of one part-per-million is noted. Relative standard deviations of less than two percent were obtained for analyzed standard chloride samples. Harware, software, and instrumentation are dis...

Electrogeneration of coulometric reagents: Applications to drug control

The coulometric electrogeneration of titanium(III) is applied to the quantitative reduction of quinone and naphthoquinone compounds of biological interest. Current efficiencies of 100% are obtained at a platinum cathode with titanium tetrachloride as supporting electrolyte in strong acidic media. Benzoquinones, which can be partially or totally destroyed in such media, are determined by using a mixture of TiCl4 and EDTANa4. The choice of experimental parameters is discussed in detail. For oxidimetric determinations, silver(II), which is well known as a very strong oxidizing agent (E0+1.90 Vvs. NHE), is produced with 100% current efficiency on a gold anode at low temperature (−10° C). The best conditions for the electrogeneration of vanadium(V) from vanadyl sulphate in dilute sulphuric acid have also been investigated. The use of amperometric or potentiometric end-point detection is discussed. Organic compounds such as hydroquinone and hydrazide derivatives can be titrated with a good accuracy.

Oxidation with permanganate in presence of fluoride: Determination of hypophosphite

A rapid method is described for the determination of hypophosphite by oxidation with permanganate in acid medium in the presence of fluoride to prevent formation of insoluble oxides of manganese. The optimum conditions for visual and potentiometric end-point detection are given. Hypophosphite is oxidized to H 2PO − 3. Under optimum conditions the titrations are fast and exhibit a reasonable potential change at the end-point. The method demonstrates the feasibility of determining amounts of H 2PO − 2 corresponding to 0.08–7 mg of phosphorus.

A new titrant for perchlorate: Cetyltrimethylammonium bromide

Cetyltrimethylammonium bromide is used in the precipitation titration of perchlorate, with potentiometric end-point detection. A perchlorate, fluoroborate or nitrate ion-selective electrode may be used. The method is more sensitive than the commonly used titration with tetraphenylarsonium chloride. It can be used over the pH range from 1.20 to at least 12.8. The titrant is much cheaper than tetraphenylarsonium chloride.

A new method for the macro- and microdetermination of tri- and tetrathionate

A rapid and precise method is described for the determination of tri- and tetrathionate. It is based on oxidation of S3O62− or S4O62− with KMnO4 in sulphuric acid medium in the presence of fluoride, required for preventing the formation of insoluble oxides of manganese. The optimum conditions for both the visual and potentiometric end-point detection are 0.1–0.16 M H2SO4 and 0.24–0.38 M NaF. Trithionate is oxidized to sulphate as an end product, whereas the oxidation product of tetrathionate comprises dithionate and sulphate according to[Formula: see text]Examination of the potentiometric titrations and the spectrophotometric scans of samples being titrated showed the presence of intermediate equilibria in solution. The species produced are identified and a theory is given for the net reactions. The method is thoroughly dependable for the determination of amounts of S3O62− or S4O62− corresponding to 0.1–10 mg of sulphur.

The influence of some organic complexing agents on the potential of copper(II) - selective electrodes. application of the silicone rubber-based electrode to the determination of citrate ion and 8-hydroxyquinoline

The behaviour of the silicone rubber-based copper(II)-selective electrode in the presence of complexing agents is discussed. The electrode shows well defined responses to several complexing agents in solutions practically free of copper(II) ions. Titrimetric determinations of citrates and 8-hydroxyquinoline with potentiometric end-point detection are described.

Oxidation with permanganate in acid medium containing fluoride: determination of bisulphite

The factors affecting the success of both visual and potentiometric end-point detection in titration of bisulphite with permanganate in the presence of fluoride are examined. The optimum conditions are 0·02 M H 2SO 4 and 0·24–0·38 M NaF. The oxidation product comprises dithionate and sulphate according to the overall reaction MnO 4 − + H + + 2HF 2 − + 3HSO 3 − ⇌ MnF 4 − + S 2O 6 2− + SO 4 2− + 3H 2O. The reverse titration is also satisfactory, but proceeds quantitatively according to MnO 4 2− + 2HF 2 − + 2HSO 3 − ⇌ MnF 4 − + 2SO 4 2− + 2H 2O.

The behaviour of tungsten electrodes in a mixture of acetic acid and acetic anhydride

Tungsten electrodes have advantageously been used for potentiometric end-point detection in perchloric acid titration of bases in a mixture of acetic acid and acetic anhydride. They have also given good results in biamperometric detection of the equivalence point in continuous coulometric titration of small quantities of bases and acids in the same solvent. Tungsten electrodes in the presence of quinhydrone behave like platinum electrodes, but in biamperometric end-point determination in the absence of quinhydrone it is better to remove the oxide layer from their surface. Some other factors affecting their behaviour have also been studied. Errors in determination do not exceed ±2% even in titration of very small quantities of substances.

Voltammetric behaviour of the nitrosodisulfonate/hydroxylaminedisulfonate redox system

Electrooxidation of hydroxylaminedisulfonate and electroreduction of nitrosodisulfonate on a platinized platinum electrode in basic media has been investigated by various voltammetric techniques. Well developed, reversible and diffusion controlled waves were obtained by using the platinum microelectrode with periodical renewal of the diffusion layer (DLPRE). The reduction of nitrosodisulfonate to hydroxylaminedisulfonate by vanadyl sulfate in basic solution has been utilized for the direct determination of nitrosodisulfonate. The titration was carried out by using amperometric, biamperometric and potentiometric end-point detection.

Use of polarized quinhydrone electrodes for potentiometric end-point detection in continuous coulometric titration of bases in non-aqueous media

A potentiometric technique for monitoring coulometric titrations of small quantities of bases in 0.1M solution of sodium perchlorate in a mixture of acetic acid and acetic anhydride has been developed. In the indicating system two polarized quinhydrone electrodes are used. The titration end-point is indicated by a potential maximum due to the concentration polarization at the indicating electrodes. The effect of the following factors on the accuracy of the method has been studied: pretreatment of the indicating electrodes, magnitude of the polarization current, generation current, relative position of electrodes in the titration cell and amount of water in the system titrated. Quantities of 2.4 × 10−6–5 × 10−5 equiv of bases were titrated by the method. Errors did not exceed ±2%.

The interference of heteronuclear chromium(III) tartrate complexes in the EDTA titration of cobalt(II), copper(II), zinc(II) and cadmium(II)

When present together in solution, chromium(III) and tartrate can interfere seriously in the titration of Co(II), Cu(II), Zn(II) and Cd(II) with EDTA. Ternary (heteronuclear) tartrate complexes containing Cr(III) and bivalent metal ion in the ratio 1:1 are formed. The conditions for the formation of these complexes have been investigated. Cadmium(II) can be determined without interference by employing potentiometric end-point detection.

Voltammetric behaviour of the nitrosodisulfonate/hydroxylaminedisulfonate redox system

Summary Electrooxidation of hydroxylaminedisulfonate and electroreduction of nitrosodisulfonate on a platinized platinum electrode in basic media has been investigated by various voltammetric techniques. Well developed, reversible and diffusion controlled waves were obtained by using the platinum microelectrode with periodical renewal of the diffusion layer (DLPRE). The reduction of nitrosodisulfonate to hydroxylaminedisulfonate by vanadyl sulfate in basic solution has been utilized for the direct determination of nitrosodisulfonate. The titration was carried out by using amperometric, biamperometric and potentiometric end-point detection.

Coulometric trace determination of water by using Karl Fischer reagent and potentiometric end-point detection

A new approach to the determination of water via the Karl Fischer reaction is described. Iodine is coulometrically generated and the end-point corresponding to a slight excess of iodine, is detected potentiometrically with a non-polarized platinum electrode. Samples of 1–500 μl containing 0·05–200 μg of water were analysed with a standard deviation of 0·015 μg in the range 0·05–20 μg of H 2O. A specially constructed electrolysis cell was used in combination with an LKB 16300 Coulometric Analyzer and the time for a complete analysis was 1–4 min, depending on sample size. The reagent composition has been optimized in order to enhance the rate of the main reaction and to minimize the extent of side-reactions. Decreasing the temperature reduced the extent of side-reactions. The displacement of end-point potential on dilution was studied and a correction is discussed.