| Reference Electrodes |
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Reference Electrode Care
The reference electrode must also be kept clean. In general, most electrode problems can be traced back to the reference electrode. Cleaning and rinse solutions are the same as for the glass electrode.
The electrode must always be filled with the salt bridge solution. For most electrodes, saturated potassium chloride, KCl, is normally used. The presence of KCl crystals in the salt bridge assures saturation.
In certain cases, the salt bridge solution may be different than saturated KCl, depending on the special nature of the reference electrode, i.e., the need for a chloride free solution or for non-aqueous solutions. In these instances, potassium sulfate or lithium chloride solutions will be used, respectively. When reference electrodes with a double salt bridge are used , saturated potassium chloride is normally found in the inner salt bridge, while the outer salt bridge contains a suitable salt of high concentration, such as KNO3, NH4NO3, or Li-Acetate.
The reference electrode should preferably be stored in a small beaker containing the salt bridge solution for short term storage. For long term storage, the electrode should be rinsed, dried, and stored with the end cap on and the rubber band covering the filling hole in place.
The solution in the salt bridge should always be on a higher level than the solution to be measured, as infiltration of the sample solution may occur in the salt bridge, that is, the direction of flow should always be from the salt bridge into the sample solution. If this cannot always be achieved, monthly changing the salt bridge solution should be the norm.
Trapped air bubbles can also cause malfunctions. These bubbles can be removed by gently tapping the electrode or shaking it downward as one would a clinical thermometer.
The useful lifetime of a reference electrode depends on the maintenance and care given the electrode. The electrode should never be allowed to dry out, the junction should be kept clean, and the salt bridge should always be filled to the level intended by the manufacturer. With proper maintenance, the lifetime for a reference electrode is indefinite, but usually greater than two years.
By providing good maintenance care to the electrodes, proper calibration should be able to be performed easily. If there is a continued problem, the electrodes should be replaced or examined again.
When performing a calibration with two buffers, stability should occur within approximately one minute in each case. The zero point and sensitivity should be written down after each calibration since a large deviation from one calibration to the next indicates a problem.
