B. Fleet

Electrochemical behaviour of organotin compounds: Part I. Application to the determination of trialkyl- and triaryltin derivatives

Abstract The electrochemical behaviour of triphenyltin and bis(tri-n-butyltin) oxide (TBTO) in 50% (v/v) ethanol solution has been investigated by various electrochemical techniques including d.c. polarography, cyclic voltammetry and controlled potential coulometry. TBTO undergoes slow hydrolysis producing tributyltin hydroxide. The first electrochemical step involves reduction of tributyltin hydroxide forming a radical which is strongly adsorbed onto the DME giving rise to an adsorption prewave. The radical undergoes further reduction in the second step along with the unhydrolysed TBTO molecules. The products have been found to be adsorbed at the electrode surface. A mechanism of reduction is proposed and a polarographic method has been developed for determining triphenyltin and TBTO down to submicrogram level. The method has been used for determining Fentin residue in formulation samples.

Comparative study of glassy carbon as an electrode material

There have often been contradications reported in regard to the efficacy of glassy carbon in voltammetric applications. The problem stems from the fact that there are a large variety of carbons available from various manufacturers that vary in their bulk structure, particularly in the degree of compactness. The extent of compactness affects both the bulk and surface properties of glassy carbon. The latter has a bearing on the formation of surface carbon-oxygen functionalities, which influence the electrochemical response of the carbon.

A study of some matrix effects in the determination of beryllium by atomic-absorption spectroscopy in the nitrous oxide-acetylene flame

A study has been made of a number of interferences observed in the trace determination of beryllium by atomic-absorption in the nitrous oxide-acetylene flame. The major negative interference caused by the presence of excess of aluminium salts may be overcome by the use of 8-hydroxyquinoline. Magnesium and silicon also depress the Be signal, but most other metals cause enhancement. In most instances the enhancements may be made uniform by the addition of potassium ions to the sample solution.

Determination of lead in blood by hydrodynamic voltammetry in a flow injection system with wall-jet detector.

Lead is one of the most widely distributed toxic heavy metals in the environment. It is a cumulative poison, affecting the brain and nervous system. The threshold between the normal lead level and the level where physiological effects become manifest is relatively narrow. It is therefore desirable to screen exposed populations in order to identify the danger in time. The lead concentration in the blood is a measure to the total amount of lead in the body. A fast, accurate and cheap method for the determination of lead in blood is therefore needed. The conventional method used to determine lead in blood is atomic absorption. Electrochemical methods like stripping voltammetry combine high analytical sensitivity with relatively low cost for the equipment; however, electrode preparation is critical for the success of an analysis, and highly skilled personnel are needed. We describe an automated electrochemical method, using flow injection analysis with a wall-jet detector. Lead is released from its binding site in the blood by ion exchange and quantified by stripping voltammetry with a mercury film electrode (MFE). The method allows for the detection of 0.05 ppm Pb(2+) with an accuracy of about 10%. Electrode poisoning by proteins from the blood can be effectively suppressed when a MFE modified with a Nafion(R)-membrane coating is used. Such modified electrodes can be activated in the solution without further treatment, and used for more than 100 analyses before they have to be replaced. A solid matrix MFE with a Nafion(R)-membrane and all necessary chemicals for mercury film formation and lead release has been developed. Such electrodes are discussed as disposable electrodes for a portable blood lead detector.

An ion-selective electrode system for continuously monitoring cyanide ion, based on a computerized gran plot technique

A procedure for the continuous monitoring of cyanide ion with an ion-selective electrode is described, based on the use of the Gran plot standard-addition technique. The mean concentration of the sample reservoir is measured continuously during a time span of 6 min. The use of a computer programme facilitates calculation of the results. Because the combined weights of several data points are used to calculate the unknown concentration, random errors tend to be eliminated and in addition there is no need for reference calibration curves.

The Determination of Low Levels of Cyanide Ion Using a Silver Responsive Ion Selective Electrode

Abstract An analysis of the potentiometric titration curves for the silver-cyanide system indicates two possible approaches to the determination of cyanide ion at low levels. Both involve an indirect measurement of the silver ion in equilibrium with argentocyanide complex. These procedures are considerably more sensitive than the conventional method using a “silver iodide” cyanide responsive electrode.

Electrochemical behaviour of organotin compounds: Part II. Dialkyltin dicarboxylates

Abstract Electrochemical behaviour of dialkyltin compounds in 80% (v/v) ethanol has been investigated by different electrochemical techniques such as polarography, cyclic voltammetry and controlled potential coulometry and it has been found to give three polarographic reduction waves. The first step involves the formation of an ion-radical which is further reduced in the second step to the dibutyltin diradical. Dibutyltin diradical undergoes polymerization as well as further reduction in two parallel processes. A procedure has been developed for determining these compounds down to p.p.b. level.

Some observations on the analytical usefulness of electrochemiluminescence for the determination of microgram amounts of aromatic hydrocarbons

Measurement of the electrogenerated chemiluminescence of twenty-four aromatic compounds in dimethylformamide solution has been investigated as a potential analytical technique for their determination. The emission spectra, calibration results and limits of determination are presented. Experimental requirements and optimum conditions for the electrogeneration of the light-emitting species are described.

Use of electrochemical detection in normal-phase high performance liquid chromatography

Abstract The application of electrochemical detection to normal-phase liquid chromatography (using non-aqueous eluents of low dielectric constant) holds considerable potential for the determination of a number of important organic compounds. By choosing an appropriate supporting electrolyte and a modified reference electrode, high sensitivity and a large potential working range is attainable. The efficacy of electrochemical detection in normal-phase liquid chromatography is demonstrated in its application to the determination of phenols.

Electrochemical behaviour of organotin compounds: Part III. Dialkyltin mercaptocarboxylates

Abstract Electrochemical behaviour of di-n-octyltin dithioglycolate has been investigated in acetate buffer (pH 7.0) containing 80% (v/v) ethanol. It has been found to give two well-defined polarographic waves, one of which is anodic and involves two-electron oxidation of the mercaptide. The other wave has been found to be cathodic and is due to one-electron reduction of the dioctyltin compound to a free radical. Strong adsorption of the compound at the DME was indicated by depression in its drop time curve. A mechanism of the electrode process is postulated and a method for detection of these compounds down to p.p.m. level has been developed.