Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1995-09-08
1997-09-30
Bell, Bruce F.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
204415, 204290R, 204434, 436 73, 436 74, 436 77, G01N 2726
Patent
active
056722575
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method of electrochemical analysis of metals and also to apparatus for use in performance of the method. The invention relates particularly to analysis of trace metals which may occur in biological and chemical samples. Such samples may include human and animal blood, plasma, serum and tissue samples, industrial and domestic waste water, process samples, sewage, food, drinking water, soil, surface and ground water, paint, dust, petrochemicals and air. The invention is particularly applicable to analysis of heavy metals, including transition lanthanide and actinide elements. Group 3 and 4 metals, including tin and lead may also be assayed.
BACKGROUND OF THE INVENTION
Electrochemical methods of metal analysis which have been used include anodic and cathodic, amperometric and potentiometric stripping analysis. A common problem associated with these techniques when used for analysis of trace metals in biological samples is that the metals bind strongly to components of the sample making direct measurement impossible. It has been necessary to digest the biological sample in order to release the metal or to use other similar metals to saturate binding sites. Acid hydrolysis together with addition of chromium, mercury and or calcium has been used to release lead from blood samples allowing measurement by anodic stripping analysis. A further problem which has been encountered in electrochemical methods for analysis of trace metals and biological samples is that the components of the sample, whether or not digested, may have a detrimental effect on the electrochemical processes which occur at the surface of the electrode. This can be overcome by high dilution of the specimen but such dilution has a detrimental effect on assay sensitivity. Traditional thin layer mercury electrode based analyses are subject to variation of the analyte solution volume and are reliant on highly controlled diffusion characteristics.
DESCRIPTION OF THE INVENTION
According to a first aspect of the present invention apparatus for electrochemical metal analysis includes a laminated electrode having a layer of mercury or of a mercury compound or salt supported thereon.
The laminated electrode is preferably formed by printing.
The electrode may comprise a printed carbon electrode for example a screen printed or ink jet printed electrode where the carbon layer is overlayed upon one or more electrically conductive tracks. Other forms of printing or laminating techniques may be employed. The conductive tracks, carbon layer and mercury layer may be each conveniently applied to a substrate by successive printing or laminating steps.
The mercury layer may comprise a layer of permeable polymeric material in which mercury or the mercury compound or salt is dispersed. Manufacture of such a layer is facilitated because mercury in the form of a mercuric or mercurous salt or other mercury compound for example a complex can be applied dissolved in a layer of the polymer deposited onto the electrode. The salt or compound is converted to metallic mercury by electrochemical reduction in use thereby forming a thin metallic layer with excellent electrochemical properties. Diffusion of the mercuric or mercurous salts into the bulk solution during assay is prevented or substantially reduced by the presence of the polymer layer. This affords an advantage in relation to an arrangement including an electrode with a superficial mercury layer formed for example by plating. Toxological problems due to mercury vapour are minimized and contamination by absorption of impurities into the metallic layer on storage is avoided. Dry storage is facilitated.
The mercury layer may comprise an amalgam. Amalgams with metals such as gallium reduce the interaction between analytes such as zinc and copper on the electrode.
Polymers which may be used in the permeable layers include: hydroxyethyl cellulose, ethyl hydroxyethyl cellulose, ethyl cellulose, cellulose nitrate, cellulose acetate, polyvinyl acetate, polyvinyl alcohol,
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Birch Stephen
Bolbot John
D'Costa Eric
Higgins Irving John
Bell Bruce F.
Cranfield Biotechnology Ltd.
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