Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – For ion concentration
Patent
1996-10-15
1998-09-29
Bell, Bruce F.
Electrolysis: processes, compositions used therein, and methods
Electrolytic analysis or testing
For ion concentration
204415, 204418, 2057895, 205792, 205793, 422 8203, 436 73, 436 74, 436 81, 436 83, 436 84, 436808, G01N 2726
Patent
active
058142053
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/GB95/00269 filed on Feb. 10, 1995.
FIELD OF THE INVENTION
This invention relates to devices and methods for measuring the quantity of metal ions in solution, particularly (but not exclusively) the measurement of lead in blood.
BACKGROUND TO THE INVENTION
It has been well known for many years that lead is a toxic element and can have a number of serious health effects. Young children are especially at risk from lead poisoning. They can be exposed to lead from sources such as water (lead pipes), food, and air (leaded petrol). Old paint can contain a high concentration of lead and the most common cause of lead poisoning in young children is from eating paint chippings or dust from the walls or windows of old houses.
In the United States of America the Center for Disease Control (CDC) considers lead poisoning such a serious problem that it recommends all children in the country under 6 years of age be screened for lead. The amount of lead which a child has been exposed to is determined by measuring the concentration of lead in the child's blood. Over the years, as more has been learned about the adverse effect of lead on children, the blood lead concentration considered safe has steadily declined. In 1985 the CDC considered a lead concentration of less than 25 .mu.g/dl to be acceptable. In 1991 the CDC lowered the safe lead level to 10 .mu.g/dl.
Until recently much of the screening for lead poisoning was done using a fluorometric method called the zinc protoporphyrin test. This method is quick and cheap but is not accurate or sensitive enough for measuring lead at the new lower limit of 10 .mu.g/dl.
Atomic absorption spectroscopy (AA) can be used to measure lead in blood very accurately at low concentrations but the method is not practicable for screening because the instrument is large, very expensive, and requires a highly trained operator.
The electrochemical method of anodic stripping voltametry (ASV) is another way of measuring lead in blood. In ASV, an electrode in contact with a solution to be tested is held at a negative potential for a sufficient period of time to reduce metal ions in the solution and concentrate them at the electrode. The potential is then ramped or scanned in the positive direction and any metals present will be stripped from the electrode when the unique oxidation potential of the respective metal is reached. The current produced during the stripping of each metal is proportional to the concentration of that metal in the test solution. Commercial ASV instruments are available but they are large, expensive, and not particularly accurate when used for measuring low concentrations of lead in blood.
The CDC is now actively encouraging development of a system which is small, portable, cheap, and easy to use, but can measure low concentrations of lead in blood with good accuracy and precision. At the present time there are no commercially available systems which meet these criteria, but this invention relates to a system which shows promise of meeting the required criteria.
SUMMARY OF THE INVENTION
In one aspect, the invention provides a device for measuring the quantity of ions of a predetermined metallic element which are present in a solution, the device comprising a mercury-free electrode separated from the solution by a layer of material which permits passage therethrough of the ions to be measured.
A preferred embodiment of the new system, designed for measuring lead in blood, uses a small, portable meter into which safely disposable cheap electrode strips are placed. A small volume of blood is added to a tube containing acid. This is mixed briefly to acidify the blood and release any bound lead. A drop of acidified blood is placed on the electrode strip and a button on the meter is pushed to start the analysis. In 2 or 3 minutes, the lead concentration in that sample of blood is displayed on the meter. A fresh electrode strip is used for each blood lead test, the used strips being disposable without environmental problems.
The improvements
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Ackland Martin Robert
Cordeiro Lucinda
McAleer Jerome Francis
Plotkin Elliot Verne
Bell Bruce F.
Palintest Limited
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