RESUMEN
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.
RESUMEN
Stricter environmental controls on the emission and discharge of chemical pollutants are creating an increased demand for the development of improved chemical sensor devices. Although electrochemical sensors show great promise for this task, their utility has been constrained by a number of practical problems, the most serious being the effect of surface adsorption of impurities leading to non-reproducible response. This review presents a survey of recent advances in electrochemical sensor technology which have attempted to improve the performance of these devices. Three main areas of development have been addressed; advances in sensor design and measurement techniques, novel approaches to conferring electrode selectivity and the use of microminiaturization and microelectronics fabrication techniques. Recent applications and future prospects for the measurement of toxic metals, organics and gases including volatile organic compounds are surveyed.
Asunto(s)
Medicina Aeroespacial , Administración de Personal , Selección de Personal , Femenino , Humanos , Masculino , Estados Unidos , Recursos HumanosRESUMEN
A novel system for semi-automated potentiometric analysis by gradient titration has been devised. In this technique both the reagent gradient generation and the titration are carried out in the sample container. The determination of chloride ion, with two ion-selective electrodes used simultaneously as an end-point sensor, is chosen to illustrate the technique.
RESUMEN
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.
RESUMEN
A new approach to the automated determination of sodium hypochlorite and hydrogen peroxide is described, based on the use of a porous catalytic silver electrode. The principle of both methods involves the quantitative liberation of oxygen, which is measured coulometrically by the electrode. The procedures are suitable for the continuous monitoring of the contents of bleaching baths.
RESUMEN
A capillary burner supporting a nitrogen/hydrogen diffusion flame has been evaluated as a possible means of detection for several volatile fluorides after their gas-chromatographic separation. The fluorides of As, B, C, Ge, I, Mo, P, Re, S, Sb, Se, Si, Te and W were formed by the reaction of the element with chlorine trifluoride, and the intense molecular emission given by each was recorded. An attempt was made to identify the emitting species.
RESUMEN
An apparatus for automatic stripping voltammetry is described. The polarograph unit (sweep generator, potentiostat, and current read-out) is constructed from operational amplifier modules and the various operations of sample injection, pre-electrolysis, stripping, etc are controlled by a cam cycle-timer. Application to the determination of submicrogram concentrations of triphenyltin acetate and hydroxide is described.
Asunto(s)
Transporte Biológico , Membranas Artificiales , Berilio , Calcio , Electrodos , Magnesio , PotenciometríaRESUMEN
The study of adsorption-desorption phenomena represents an important extension to the range of organic compounds that can be determined by electrochemical methods. The present work has utilized this approach for the determination of a range of methylcarbamate insecticides. The tensammetric behaviour of this class of compound at the mercury electrode has been investigated by a.c. polarography and the optimum experimental conditions for their analytical determination have been derived. Cyclic voltammetry has also been used to study the electrode process and by using the peak obtained on the cathodic sweep it was possible to extend the limit of detection to the ppm level.
RESUMEN
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.
RESUMEN
A wide range of olefins can be determined by a.c. polarography of their addition compounds with mercuric acetate. The first step in the reduction of these compounds is a reversible, one-electron process to form the organo-mercury radical and gives a well defined a.c. peak. The optimum conditions for the determination of a representative selection of olefins has been established.
RESUMEN
The evaluation of a specific gas Chromatographie detector for carbonyl compounds is described. This is based on the polarographic reduction of the Girard T hydrazone derivative which is formed when the carbonyl compound is absorbed in a buffered supporting electrolyte containing the carbonyl reagent. The detector was used to monitor the separation of a homologous series of alkanals.
RESUMEN
An account is given of the quantitative determination of certain fused-ring aromatic hydrocarbons by means of the electroluminescence induced by application of a small a.c. voltage to inert electrodes placed in a solution of the hydrocarbon in dimethylformamide.
RESUMEN
Visual compleximetric methods for the titration of calcium in the presence of magnesium have been based either on masking the magnesium or using an indirect indicator procedure, e.g., the system Zn-EGTA-Zincon. In the proposed method these two approaches are combined. Zn-EGTA complex is added to the mixture and the zinc liberated in the calcium replacement reaction is titrated with EGTA after the magnesium has been masked with fluoride ion.