Catalytic microdetermination of mercury

An automatic spectrophotometric reaction-rate method is described for the microdetermination of mercury. The method is based on the catalytic effect of mercury on the reaction of ferrocyanide with nitrosobenzene. The time required for production of a small fixed amount of the violet product as given by a preselected change in the output voltage of a photoconductive circuit, is measured automatically and related directly to the mercury concentration. The possibility of masking interfering ions with EDTA was examined. Amounts of mercury in the range 0.25–2.5 /smg, were determined with relative errors of 1–2% in measurement times of only 15–120 sec. Results obtained with mercurial compounds, treated with bromine water, were within 1–2% of the theoretical values and results obtained with pharmaceutical preparations were within the range assigned to those preparations.     

Semiautomatic catalytic titration of palladium and gold(III)

Microchimica Acta - A semiautomatic potentiometric method is described for the catalytic titrimetric determination ofμg amounts of palladium or gold. The method is based on the inhibitory...     

Kinetic ultramicrodetermination of chromium(III) and osmium(VIII) based on their accelerating effect on the periodate-arsenite reaction

Summary A spectrophotometric kinetic method is described for the ultramicrodetermination of chromium (III) and osmium (VIII) based on their promoting and catalytic effect respectively on the periodate — arsenite reaction. For chromium(III) determination the decrease in absorbance within a fixed period of time is related directly to the chromium concentration. For osmium (VIII) determination the time required for the reaction to consume a fixed amount of periodate is measured automatically and related directly to the osmium concentration. Ultramicroamounts of chromium(III) in the 10^–6–10^–5 M level and of osmium(VIII) in the 10^–8–10^–7 M level were determined with a mean error of about 2%. The method has been applied to the determination of chromium in chrome ores.

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Zusammenfassung Eine kinetische Methode zur Ultramikrobestimmung von Chrom(III) und Osmium(VIII) auf der Grundlage ihrer beschleunigenden bzw. katalytischen Wirkung auf die Perjodat-Arsenit-Reaktion wurde beschrieben. Für Chrom dient die Abnahme der Extinktion innerhalb einer bestimmten Zeitspanne als Maß der Konzentration. Bei der Bestimmung von Osmium(VIII) wird die Zeit für den Verbrauch einer bestimmten Menge Perjodat automatisch gemessen. Sie entspricht direkt der Osmiumkonzentration. Ultramikromengen Cr(III) in der Größenordnung 10^–6–10^–5 M und Os(VIII) in der Größenordnung 10^–8–10^–7 M sind mit einem Fehler von ungefähr 2% bestimmbar. Die Methode wurde zur Chrombestimmung in Erzen angewendet.

     

Automated stopped-flow system in pharmaceutical and clinical analysis : Kinetic determination of acetaminophen in formulations and serum by using the iron(II)—2,4,6-tris(2-pyridyl)-s-triazine

The development of automated stopped-flow spectrophotometric systems, their potential in automated routine determinations using kinetic and fast equilibrium techniques and several examples of applications are briefly reviewed. The use of a compact, inexpensive laboratory-made stopped-flow system for the measurement of reaction rates and a fast equilibrium method for the determination of acetaminophen in formulations and serum are described. The reaction-rate method is based on monitoring the oxidation of acetaminophen by iron(III) in the presence of the chelating agent 2,4,6-tris(2-pyridyl)-s-triazine to form a highly absorbing complex of iron(II). The calibration graph is linear in the range 20–200 μg ml^?1, with a precision of 0.8–2.6%, a detection limit of 5.5 μg ml^?1 and a measurement throughput of 120 per hour. Common excipients do not interfere and the analysis of commercial formulations gave results similar to those of a reference method. The optimization of the experimental conditions was done by a kinetic study of the reaction and some kinetic parameters are given.The method for the determination of acetaminophen in serum is based on a rapid measurement of the absorbance of the reaction mixture after a delay time of 15 s in the presence of chlorpromazine, which catalyses the reaction. Acetaminophen is isolated by extraction with ethyl acetate and the calibration graph is linear in the range 0.5–6 μg ml^?1 with a detection limit of 0.04 μg ml^?1 and a precision of 1.5%. The proposed method showed a decreased interference from drugs that also react with iron(III).     

Kinetic study of the acid hydrolysis of sucrose and lactose and kinetic determination of sucrose using a periodate-selective electrode

A novel procedure for the kinetic study of the acid hydrolysis of sucrose and lactose has been developed. The parameter observed is the rate of the reaction of periodate with quenched aliquots of the solution in which hydrolysis takes place. This rate measured with a periodate-selective electrode, and is expressed in terms of rate of increase in potential (gDE/Δt). Based on the observed differences in the hydrolysis rate, a kinetic method has been developed for the determination of sucrose in the presence of other carbohydrates in the concentration range 0.01–0.10 M with an average error of 1.4%. The method has been applied to the determination of sucrose in milk products and soft drinks.     

Potentiometric determination of nicotine in tobacco products with a nicotine-sensitive liquid membrane electrode

A simple potentiometric method with standard additions is described for the rapid determination of nicotine in tobacco products. A nicotine-sensitive electrode with a liquid membrane of nicotine hydrogen tetra(m-chlorophenyl)borate dissolved in o-nitrotoluene is used. The electrode exhibits near-Nernstian response to monoprotonated nicotine cation activity from 0.08 to 10^-5 M, in the pH range 4–7. Nicotine down to 2 mg per g of sample can be determined with a standard deviation of about 0.5 mg of nicotine. Comparison with an official method gave satisfactory results.     

Kinetic determination of EDTA and citrate by the displacement of fluoride from Al(3+)F(-) complexes and use of a fluoride ion-selective electrode

The displacement of fluoride from its aluminium complexes by the action of EDTA, citrate and other ligands is a relatively slow process which can be monitored potentiometrically with a fluoride ion-selective electrode. Some characteristics of these reactions are presented. There is evidence that [AlF](2+) reacts with the competitive ligand faster than the simple free (hydrated) Al(3+) species does. The relative rates of release of fluoride by the action of various aminopolycarboxylic acids have been determined. Potentiometric reaction-rate methods have been developed for the determination of 0.2-1.5 mumole of EDTA and 0.1-1.0 mumole of citric acid, with average relative errors of approximately 3%.     

Potentiometric titration of fluoride,sulfate, chromate,molybdate, tungstate,oxalate, phosphate,pyrophosphate and hexacyanoferrate(II) ions with lead(II) solutions and a fluoride-selective electrode

A semi-automatic potentiometric method is described for the direct titration of fluoride with lead(II) solutions in the presence of added chloride. Sulfate, chromate, molybdate, tungstate, oxalate, phosphate, pyrophosphate, and hexacyanoferrate(II) are titrated similarly in the presence of added chloride and fluoride. A fluoride-selective electrode is used to detect the end-points. Fluoride in the range 0.57–5.7 mg can be determined with a precision of about 0.3%. The other ions can be determined in the range 0.025–0.30 mmol with a precision of 0.5–1%.     

Construction,analytical study and application of a new chloramine-t selective electrode

A chloramine-T (CAT) selective electrode with a liquid membrane of nickel batho-phenanthroline—chloramine-T dissolved in 2-nitro-p-cymene is described. The liquid membrane electrode exhibits rapid and near Nernstian response to chloramine-T activity from 10^-1 to 10^-4 M. The response is unaffected by pH in the range 5–9. Major interferences are penodate and perchlorate. In analytical applications, direct potentiometnc methods for the determination of chloramme-T, ascorbic acid, and arsenic(III), and a titnmetric method for ascorbic acid are described. Ascorbic acid and arsenic(IU) in the ranges 0.4–40 and 0.5–2 mg, respectively, can be determined with relative errors of 1–2%. The method has been applied to the determination of ascorbic acid in pharmaceutical preparations.