Construction,assessment and applications of a dichromate-selective liquid membrane electrode based on tetrapentylammonium dichromate

A dichromate-selective liquid-membrane electrode based on tetrapentylammonium dichromate dissolved in 2-nitrotoluene is described. The electrode exhibits rapid and linear response to the activity of Cr(VI) anions in the range 5 × 10^?4–2 × 10.2 M dichromate; the slopes of the calibration graphs depend on the acidity. The electrode is useful for end-point indication in titrations of iron(II), arsenic(III), ascorbic acid, thiobarbituric acid, thiourea, and cysteine with dichromate. The electrode is also used as indicator electrode in a potentiometric reaction-rate method for the determination of hydroxyl-containing organic compounds, based on their oxidation by dichromate in acidic solution; ethanol, isopropanol, ethylene glycol, propylene glycol, butylene glycol, and several carbohydrates were determined with a mean error of 1%. The method is applied to determine the ethanol content of alcoholic beverages. Kinetic data are given for the dichromate/ethanol reaction.     

Kinetic microdetermination of copper in urine,thiosulfate, nitrilotriacetic acid,and ethyleneglycolbis (2-aminoethylether)-NNN'N'-tetraacetic acid

Summary An automatic spectrophotometric kinetic method is described for the ultramicrodetermination of copper. The method is based on the catalytic effect of copper(II) on the periodate-thiosulfate reaction. The method is also used for the determination of nitrilotriacetic acid (NTA) and ethyleneglycol-bis(2-aminoethylether)-NNN'-N'-tetraacetic acid (EGTA), on the basis of their inhibitory effect on the copper-catalyzed periodate-thiosulfate reaction, and of thiosulfate. The time required for the reaction to consume a fixed amount of periodate is measured automatically and related directly to the catalyst or inhibitor or substrate concentration. Ultramicroamounts of copper, NTA and EGTA, in the 10^–7–10^–6 M level, and microamounts of thiosulfate in the 10^–4–10^–3 M level were determined with relative errors of about 2%. The method has been applied to the determination of copper in urine.

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Zusammenfassung Eine automatische spektrophotometrische Methode für die Ultramikrobestimmung von Kupfer wurde beschrieben. Sie beruht auf dem katalytischen Effekt des Kupfers bei der Reaktion von Perjodat mit Thiosulfat. Das Verfahren dient auch zur Bestimmung von Nitrilotriessigsäure und Äthylenglykol-bis(2-Aminoäthyläther)-NNN'N'-tetraessigsäure auf der Grundlage ihrer hemmenden Wirkung auf die erwähnte Katalyse sowie zur Bestimmung von Thiosulfat. Die für den Verbrauch einer bestimmten Menge Perjodat erforderliche Zeit wird automatisch gemessen und steht in direkter Beziehung zur Konzentration des Katalysators, des Inhibitors bzw. des Substrates. Ultramikromengen Kupfer, NTA und EGTA in der Größenordnung von 10^–7 bis 10^–6 Mol sowie Mikromengen Thiosulfat von 10^–4 bis 10^–3 Mol lassen sich mit einem relativen Fehler von etwa 2% bestimmen. Das Verfahren wurde zur Bestimmung von Kupfer in Harn verwendet.`

     

Enzymatic fluorimetric determination of cholic acid and chenodeoxycholic acid in aqueous solutions and blood serum using a differential kinetic method

An enzymatic fluorimetric method is described for the determination of chenodeoxycholic acid and its conjugates and of cholic acid and its conjugates in aqueous solutions and serum. The method is based on the oxidation of 7 α-hydroxy bile acids by β-NAD⁺ in the presence of 7 α-hydroxysteroid dehydrogenase; the NADH produced is monitored fluorimetrically. Chenodeoxycholic acid is determined in the presence of cholic acid by a differential kinetic procedure; the sum of the two acids (primary bile acids) is determined by an equilibrium procedure, and cholic acid is calculated by difference. The r.s.d. was ca. 3% and 10% for aqueous solutions and sera, respectively. Recoveries of chenodeoxycholic acid, cholic acid and primary bile acids added to serum samples averaged 100.5, 105.1, and 102.9%, respectively. Ten samples can be analyzed per working day.     

Automatic catalytic titration of silver

An automatic method is described for the catalytic titrimetric determination of microgram amounts of silver. The method is simple and accurate, and is based on the inhibitory effect of silver ions on the iodide-catalysed Ce(IV)-As(III) reaction. The end-point of titration with iodide is determined either automatically by the second- derivative technique or from the recorded potentiometric or spectrophotometric curves. Microamounts of silver in the range 1–2000 μg were determined with relative errors of about 0.7%.     

Determination of serum lactic dehydrogenase by an automatic reaction-rate method

An automatic spectrophotometric reaction-rate method is described for the determination of lactic dehydrogenase (LDH) in blood serum. The method is based on the oxidation of lactic acid in the presence of LDH and diphosphopyridine nucleotide (DPN) to form an absorbing species DPNH. The time required for a small fixed (about 0.06 unit) change in absorbance is measured automatically and related to the LDH concentration. Automatic results obtained on samples containing 0.05 to 0.2 ml of serum show good proportionality and a coefficient of variation of 1.3%. Serum samples (0.2 ml) are analyzed at a rate of 15 to 20 per hour.     

Evaluation of the chloramine-T membrane electrode response in acidic solutions. The determination of the pKa of N-chloro-p-toluenesulfonamide (chloramine-T acid)

Measurements made with a combination of glass and chloramine-T ion-selective membrane electrodes in acidified chloramine-T solutions varying in ionic strength have been used to determine the dissociation constant of N-chloro-p-toluenesulfonamide (chloramine-T acid). Experimental data agree satisfactorily with reported values.     

Use of a periodate-sensitive perchlorate ion-selective electrode in the kinetic ultramicrodetermination of manganese(II) by means of its catalytic effect on the periodate-acetylacetone reaction

A kinetic method for the ultramicrodetermination of maganese, based on its catalytic effect on the periodate-acetylacetone reaction, is described. A perchlorate electrode is used as a periodate sensor to monitor the reaction. The time required for the potential to change by a preselected amount (10 mv) is measured automatically and related directly to the manganese concentration. Amounts of manganese in the range 40-240 ng were determined with relative errors of about 2-4%.