EDTA titration of calcium and magnesium with a calcium-selective electrode

Direct semi-automatic and automatic derivative potentiometric EDTA procedures for the determination of calcium and/or magnesium with a calcium-selective electrode are described. Calcium is titrated in the presence of magnesium at pH 12.0 and the total calcium and magnesium is determined at pH 9.7. Calcium in the range 1-8 mg and magnesium in the range 0.7-5 mg are determined semi-automatically with average errors of about 0.2 and 0.3% respectively and automatically with average errors of 0.4 and 0.7%. Titration times vary from a few seconds to a few minutes.     

Determination of vanadium(V) by direct automatic potentiometric titration with EDTA using a chemically modified electrode as a potentiometric sensor

A chemically modified electrode (CME) was prepared and studied as a potentiometric sensor for the end-point detection in the automatic titration of vanadium(V) with EDTA. The CME was constructed with a paste prepared by mixing spectral-grade graphite powder, Nujol oil and N-2-naphthoyl-N-p-tolylhydroxamic acid (NTHA). Buffer systems, pH effects and the concentration range were studied. Interference ions were separated by applying a liquid-liquid extraction procedure.The CME did not require any special conditioning before using. The electrode was constructed with very inexpensive materials and was easily made. It could be continuously used, at least two months without removing the paste.Automatic potentiometric titration curves were obtained for V(V) within 5 × 10⁻⁵ to 2 × 10⁻³ M with acceptable accuracy and precision. The developed method was applied to V(V) determination in alloys for hip prothesis.     

Determination of uranyl ion by potentiometric titration using an uranyl-selective electrode

Summary A potentiometric titration of uranyl ion is described using an uranyl selective electrode based on a membrane containing a complex of UO₂-bis[di-4-(1,1,3,3-tetra-methylbutyl)phenyl phosphate] as an ion-exchanger and tritolyl phosphate as a solvent mediator. The titrations were carried out with various titrants: sodium hydroxide, potassium fluoride and sodium salts of acetate, oxalate and citrate. The equivalence points were determined by Gran's method. Good results were obtained by using sodium oxalate as a titrant for the determination of uranium in several samples of ammonium diuranate. The results were quite comparable with those obtained by X-ray fluorescence spectrometry.     

Determination of chloride in sulphuric acid by potentiometric mercurometric titration

The chloride content of concentrated sulphuric acid is determined by mercurometric titration in 80% v/v methanol medium, with a mercury pool as indicator electrode. The method is simple, fast, accurate and reasonably sensitive (limit of detection 4.5 μg/ml), and suitable for routine application.     

Determination of bismuth(III) by direct potentiometry and potentiometric titration, with an electrode sensitive to Bi(3+)

A liquid-state ion-exchange electrode containing the chelate bismuth(III) complex with 5-mercapto-3-(naphthyl-2)-1,3,4-thiadiazole-2-thione in tetrachloroethane is applied to the determination of bismuth(III) by direct potentiometry and potentiometric titration. The influence of various interfering cations is discussed. In the presence of potassium cyanide as masking agent, Ni(II), Co(II), Cu(II), Ag(I) and Hg(II) do not interfere in the potentiometric EDTA titration. Satisfactory results have been obtained for the determination of bismuth(III) in Wood's metal and two pharmaceuticals.     

Determination of phosphorous in titanium bearing minerals by potentiometric titration using Pb-ion selective electrode

A method for phosphorous determination in titanium bearing minerals by potentiometric titration using a Pb-ion selective electrode has been developed. Sample decomposition is achieved by means of K(2)CO(3) fusion in a platinum crucible at 800 degrees C for 30 min in a muffle furnace, and subsequent leaching with water of the fused melt. The aqueous leachate is neutralised with HClO(4) and subsequent boiling. The obtained solution is used for titration with Pb(ClO(4))(2), and the Pb-ion selective electrode detects the end point. The lowest concentration determinable is 0.02% P(2)O(5) in a solid sample. The method was applied on in-house titanium bearing mineral samples and on IGS-31 ilmenite sample (British Geological Survey, UK). Synthetic samples were prepared and analysed, and phosphorous recovery is in the range 98-106%. The recovery and accuracy of the present method have been validated by spiking experiments and by comparing with the spectrophotometric values, respectively. The precision of the proposed method in terms of relative standard deviation is 2.0%.     

Characterization of di(2-ethylhexyl)thiophosphoric acid by potentiometric titration and capillary zone electrophoresis

 The acidity constant of di(2-ethylhexyl) thiophosphoric acid (DEHTPA) was investigated using potentiometric measurements with a pH glass electrode. Owing to the low solubility of DEHTPA in pure water, its concentration and acidity constants were determined by linearised pH-metric titration in 16.7% ethanol. A K_a value of (2.39±0.08)×10^-4 was obtained. Quantitative determination of DEHTPA was performed by capillary zone electrophoresis (CZE) with carbonate buffer (pH 11.0) as a background electrolyte, operating at −20 kV with direct UV detection at 210 nm. The migration time was 8.97 min and the detection limit was 5 ppm. Received: 2 September 1996/Revised: 19 November 1996/Accepted: 21 November 1996     

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.     

Determination of nickel by direct automatic potentiometric titration with EDTA and a chemically modified electrode based on a strong acid ion exchanger containing 4-(3,5-dichloro-2-pyridylazo)-1,3-diaminobenzene

A chemically modified electrode (CME) was constructed and evaluated for use as an end-point indicator in the automatic titration of Ni(II) with EDTA. The CME consisted of a graphite paste prepared by mixing a strong acid ion exchanger containing 4-(3,5-dichloro-2-pyridylazo)-1,3-diaminobenzene and graphite powder-Nujol paste. This mixture showed high mechanical resistance in strongly acidic and alkaline solutions (6 M HCl-pH 12). The CME did not require any special conditioning prior to use. It could be used over long periods (5-6 months) of continuous work without renewing either the electroactive surface or paste. In buffered solutions (pH 3-4.5), automatic direct potentiometric titrations could be carried out over a wide interval of Ni(II) concentrations, ranging from 3 to 6000 ppm, with satisfactory accuracy and precision. For practical analysis, the electrode was applied to the determination of nickel in two certified composition alloys. Interferent ions were previously separated by applying an ion-exchange procedure.     

Determination of chlorine in silicate rocks by ion-exchange chromatography and direct potentiometry with an ion-selective electrode

The method has been developed for determination of chlorine in silicate rocks by ion-exchange chromatography and an ion-selective electrode.     

Spectrophotometric determination and titration of trivalent chromium with cyclohexane diamino tetraacetic acid (disodium salt)

Summary The reaction between trivalent chromium and disodium cyclohexane diamino tetra acetate (CDTA) at the boiling temperature has proved to be a suitable one for the spectrophotometric determination of small amounts of Cr^III covering the range 10–120 ppm in purely aqueous solutions. The variation of absorbancy with concentration conforms satisfactorily with Beer's law throughout the whole range. A variety of cations and anions do not interfere with such a determination. A procedure is given for the spectrophotometric titration of Cr^III with CDTA.

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Zusammenfassung Die Reaktion zwischen dreiwertigem Chrom und Dinatriumcyclohexandiamintetraacetat (CDTA) bei Siedetemperatur wird zur spektrophotometrischen Bestimmung von kleinen Mengen Chrom (III) benutzt. Das Beersche Gesetz wird im Bereich zwischen 10 und 120 ppm erfüllt. Eine größere Anzahl verschiedener Kationen und Anionen stört die Bestimmung nicht. Die spektrophotometrische Titration wird ebenfalls beschrieben.

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on leave from University of Massachusetts, Amherst, Mass., USA.     

Gran电位滴定法测定乳酸环丙沙星

介绍了乳酸环丙沙星测定的Gran电位滴定法。采用Gran线性函数进行电位滴定,经图解外推或线性回归处理求出计量点,可直接用于测定乳酸环丙沙星原料药的含量。该法用于多批原料药的测定,结果与药典法基本一致。     

聚邻氨基对酚磺酸修饰电极测定尿酸

尿酸(UA)是核蛋白和核酸的代谢产物,人体内尿酸的水平与肝脏疾患[1]、肾病[2]以及心血管疾病[3]等有着密切的关系.因此,对人体体液中尿酸的定量分析无论在药物控制方面还是在临床诊断方面都具有重要意义.     

Determination of sulfide with chloranilic acid by biamperometric and automatic potentiometric end-point detection with a lead chloranilate selective electrode

A titrimetric method for determination of sulfide and of sulphur in steels with chloranilic acid by biamperometric and automatic potentiometric end-point detection is described. The construction of the sensor for potentiometric indication is also described. The results obtained agree with those of the iodine-thiosulfate method and with the certified values for the steels.     

Selective determination of magnesium in water with divalent ion electrode using ethyleneglycol-bis(2-aminoethylether)tetraacetic acid as a complexing agent

Summary The calculated conditional constants at pH 2 to 10 for the ethyleneglycol-bis(2-aminoethylether)-tetraacetic acid (EGTA) complexes of magnesium and other metals indicate that no significant amount of magnesium is complexed by EGTA at pH below 7. The effect of pH on the electrode potential in the presence and absence of EGTA has been studied. The optimum pH found to be 7.0. At this pH magnesium can be selectively determined with a divalent electrode in the presence of most other polyvalent metal ions. Large amounts of salts affect the activity of magnesium ion and the electrode potential. Organic amines have been studied as a base to neutralize free acids in a solution, an amount of 5×10^–2 M nitrilodiethanol could be tolerated. The plot of potential vs. concentration of magnesium from 1×10^–5 to 1×10^–1 M gives a rectilinear relationship.

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Zusammenfassung Die für pH 2 bis 10 berechneten Bildungskonstanten für die Komplexe des Magnesiums und anderer Metalle mit Äthylenglykol-bis-(2-aminoäthyläther)-tetraessigsäure (EGTA) zeigen, daß keine nennenswerten Mengen Magnesium unter pH 7 gebunden werden. Der Einfluß des pH auf das Elektrodenpotential in An- und Abwesenheit von EGTA wurde geprüft. Das pH-Optimum liegt bei 7,0. Bei diesem pH kann Mg mit einer zweiwertigen Elektrode in Anwesenheit der meisten anderen polyvalenten Metallionen selektiv bestimmt werden. Große Salzmengen beeinträchtigen die Aktivität des Mg-Ions und das Elektrodenpotential. Organische Amine wurden zur Neutralisation freier Säuren in der Lösung verwendet. 5·10^–2 Mol Nitrilodiäthanol/Liter sind tolerierbar. Potential gegen Mg-Konzentration aufgetragen ergibt zwischen 10^–5 und 10^–1 Mol Mg/1 ein geradliniges Verhältnis.

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This study was supported by Office of Saline Water, U. S. Department of Interior, Grant No. USDI 14-01-0001-1643. Presented before the Division of Water, Air and Wastes Chemistry, American Chemical Society, 161st National Meeting, March 31, 1971.     

Determination of fluoride in potable waters by ion-exchange and potentiometric titration

A procedure is described for the accurate titration of fluoride at the 1 mg l . level in potable water. The procedure employs an ion-exchange step for concentration of fluoride and removal of interfering ions, and Tb(IV) as titrant. Precision and relative error of the method are both 1%.     

Ethyleneglycol-bis(aminoethyl)tetraacetic acid in the amperometric titration of cadmium in the presence of zinc

Cadmium can be titrated amperometrically with EGTA in the presence of zinc; three modifications of the titration are described. The diffusion current of cadmium may be used to follow the titration at —0.90 or —0.70 V vs, the S.C.E, in ammoniacal or acetate-buffered medium respectively The titration may also be performed in ammoniacal solution at —0.30 V vs. the S.C.E., using copper as the amperometric indicator. The influence of iron, aluminium, magnesium, alkaline earths and lead was studied. Ascorbic acid could be used to mask iron and as an effective remover of oxygen. Under appropriate conditions cadmium could be titrated in the presence of 500-fold amounts of zinc. The titration error is approximately 0.002–0.003 ml of a 0.1 M titrant solution.