High precision titrimetry: An examination of the attainable precision

A re-examination and critical assessment of the mechanical precision of titrimetric processes, with particular reference to the drainage errors of burettes, has been made and some manipulative improvements suggested.The piputte-dilution method offers a useful improvement in the precision of volumetric methods, further increase in mechnical precision affords little or no improvement in accuracy of determination.     

Improvement of polarographic precision by a comparative technique

Summary Comparative techniques are described which give an increase in precision of 100-fold over conventional polarography. By interchanging cells during measurement, certain electrode and cell inequalities are minimized. Major constituents of many matrices may be determined ong amounts of sample with a precision as good as 2 parts in 10000. The technique is illustrated by the determination of copper, cadmium, and zinc in several materials.

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Zusammenfassung Vergleichsmethoden wurden beschrieben, mit deren Hilfe eine l00fache Steigerung der Genauigkeit der konventionellen Polarographie zu erreichen ist. Durch Wechsel der Zellen während der Messung lassen sich gewisse Einflüsse von Ungleichheiten der Zelle und der Elektrode auf ein Minimum herabsetzen. In Mikrogrammengen vieler Mehrstoffsysteme lassen sich Hauptbestandteile mit einer Genauigkeit von 2 Teilen/10000 bestimmen. Die Bestimmung von Cu, Cd und Zn in verschiedenen Proben wird beschrieben.

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Paper presented at the 1966 Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy.     

Pulse polarography

Summary The application of a pulse technique to polarography results in a further improvement in polarographic performance, the new instrument being capable of detecting reversibly reduced species at concentrations as low as 10^–8 M, and irreversibly reduced species at 5 · 10^–8 M. The new instrument also yields both derivative and normal polarograms of much improved types. We are indebted to Mr. R. J. Jacob of the Electronics Division, A.E.R.E., for invaluable assistance in the construction of the electronic equipment.     

Fournier polarography revisited

A theory for Fournier polarography and higher order harmonics is presented. This is valid for reversible systems under semi-infinite diffusion to stationary and expanding plane electrodes. The algorithm is simple, accurate and exploits the identities holding for the interfacial concentrations. The computations — minimal in nature — can be carried out easily and the results given here were evaluated taking into account the presence of harmonics to, at least, the twenty-fifth order.     

Computerized kalousek polarography

A versatile online computer-based system for Kalousek polarography features simultaneous recording of oxidation and reduction currents, averaging over successive scans, and processing of the polarographic data by curve-fitting. The accuracy for determinations of cadmium, potassium and lithium down to 10^-5 M is ± 5% for pulse rates up to 25 Hz.     

High precision NMR study of 1,1-disubstituted silacyclobutanes

The hydrogen NMR spectra of 1,1-dimethyl-, 1,1-dichloro-, 1,1-dimethoxy- and 1,1-difluoro-silacyclobutane have been analysed. A new correlation NMR instrumental technique has been used to obtain spectral parameters with very high precision.     

The polarography of amidines

Summary The polarographic properties of some aliphatic, arylaliphatic, phenoxyaliphatic and aromatic amidines have been investigated. Aliphatic and arylaliphatic amidines are not reducible in the range 0 to –1.8 volts versus the saturated calomel electrode. Phenoxyacetamidines are reduced to the phenol and acetamidine. Aromatic amidines are reduced to the benzylamine and ammonia. The half-wave potentials of both reducible classes of compound are independent of Ph over the range 7–9 Ph.     

Optimalization of doubletone polarography

Through the application of coherent fundamental frequencies, the synchronization of measuring frequency and dropping frequency, which facilitate the use of phase sensitive techniques, doubletone polarography could be developed into a highly sensitive polarographic method with a high resolution in common with all derivative methods.     

Controlled-potential differential DC polarography

Summary A brief theoretical and experimental study is presented of the polarographic technique in which a constant voltage difference (E) is maintained between two electrodes immersed in the same or identical solutions throughout the potential scan in order to obtain a derivative-like curve of differential current (i) vs. electrode potential (E). A comparison of the curves obtained by this technique with the true first derivative of the polarographic wave, as observed by operational-amplifier computation, is also given.

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Zusammenfassung Als Teil einer allgemeinen Untersuchung über die Differential-Gleichstrompolarographie mit Potentialkontrolle wird über die E -Methode berichtet, bei der eine konstante Spannungsdifferenz ( E) zwischen zwei Elektroden aufrechterhalten wird, die in dieselbe oder identische Lösungen eintauchen. Die Differenz der beiden Ströme als Funktion des Elektrodenpotentials stellt eine Kurve dar, die stellenweise der wirklichen ersten Ableitung der polarographischen Stufe ähnelt. Ein Vergleich dieser Kurven wird angegeben.

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Dedicated to Prof. Dr. M. von Stackelberg on his 70th birthday.

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Research sponsored by the U.S.Atomic Energy Commission under contract with the Union Carbide Corporation.     

Inorganic polarography in organic solvents-IV: polarography of metal oxinate complexes in various solvents

The polarography of 24 metal oxinate complexes extracted into chloroform, IBMK, and ethyl acetate has been investigated, a methanolic solution of lithium chloride being used as base electrolyte. Only 15 complexes gave rise to reduction waves, and interference-free determinations have been developed for indium and thallium(III) in chloroform, and for bismuth, molybdenum and uranium in IBMK. The use of ethyl acetate offered no special advantages, and was the least selective of the three solvents used.     

The polarography of lead styphnate

A study of the polarographic behaviour of lead styphnate has been made. It has been shown that by use of a combination of normal polarography and derivative polarography using an alternating current method it is possible to determine both lead and styphnate ions in the samesolution.