1. Field of the Invention
The present invention relates to electrochemical electrodes and, more particularly, to combination electrodes for measuring the ion concentration of solutions.
2. Description of the Prior Art
Combination electrodes comprising a sensing portion and a reference portion incorporated in a glass or a plastic structure are known in the art. One known electrode assembly for measuring pH includes a generally flat, pH-sensitive glass membrane having one face for contacting a sample to be measured and an opposite face contacting an internal electrolyte within the assembly. In addition, a liquid junction is provided between the sample and a reference electrolyte within the assembly. By virtue of its flat ion-sensing structure the electrode assembly is able to measure a small quantity of sample solution on a relatively flat surface without the need to immerse the electrode in a large volume of the solution. Thus, the electrode is particularly suited for measuring, for example, the pH of moisture on the skin of a human subject.
While electrodes of the foregoing nature have performed satisfactorily, they have been confined generally to laboratory, clinical, or other specialized applications requiring trained operating personnel. Further, the sensing portion of such prior electrode assemblies must be carefully positioned on the sample to be measured with the electrode assembly vertically oriented with respect to the sample. This is necessary to ensure that the conventional liquid junction included in the prior art electrode makes contact with the sample and to ensure that any air bubbles within the electrode assembly rise to the top thereof so as not to contact either the ion-sensitive membrane or the liquid junction. If these precautions are not taken, erroneous measurements can result. In addition, the reference electrolyte is generally consumed during normal operation of the electrode and must be periodically refilled. The refilling operation requires a skilled operator to ensure that a proper electrolyte is employed and that no contamination is introduced during the filling operation.
Recently, the need has arisen for a combination electrode assembly which can be operated over prolonged time periods at any physical orientation by non-technical operators. For example, a particular need exists in the cosmetic and hairdressing industry for an electrode assembly which can be routinely employed by hairdressers, beauty operators, and the like for monitoring the pH of a subject's hair, skin, or other body parts. The present invention provides such an assembly.