Glass electrodes rejuvenation

If the electrode is allowed to dry, it may partially lose its pH function. Therefore it is imperative that a glass electrode which is used for nonaqueous pH measurements be soaked periodically in water to rejuvenate it. Even with partial dehydration, glass electrodes function properly for a moderate time period in nonaqueous solutions having a dielectric constant as low as 2.3 (see Table A.2). 

The main concern for proper glass electrode care is to keep the glass bulb soaking in solution (see Section 3.5). If the electrode exhibits one of the following, rejuvenation may be necessary a lag... 

If this cycling fails to rejuvenate the glass electrode, a new glass surface can be generated by etching its surface. The bulb is dipped in a 20% ammonium bifluoride solution for 10 to 30 seconds and then rinsed thoroughly with water. Then the electrode is immersed in 5 M hydrochloric acid for a few seconds to remove the fluorides and rinsed again with water. 

A glass electrode response test can use the same buffer solutions as employed for the span test. After standardization of the pH meter in pH 9.18 buffer, the reference electrode tip is immersed in pH 4.01 buffer to preequilibrate for a period of 5 minutes. This eliminates any response time due to the reference electrode. After this time period, rinse the glass electrode with pH 4.01 buffer and immerse the bulb in the same buffer solution with the reference electrode. Record the pH value versus time or observe the reading after 10 seconds. The reading after the 10-second period should be 98% of the final reading that is, the meter should read 4.11 or less within the 10 seconds. If the electrode fails this test, rejuvenation may help to increase its response. Response time for electrodes is discussed in detail in Section 5.3. 

To review the expected electrode response should reach 98% of its final reading within 10 seconds when the span test is performed between two buffers the rejuvenation procedure, described in Figure 3.3, should be initiated if the glass electrode does not meet these specifications. 

If the troubleshooting procedure leads to a short-span or slow-responding glass electrode, the rejuvenation of the glass bulb or electrode replacement is required. If the problem is the result of a faulty pH meter, only proper service will resolve the problem. No matter which component is the cause of difficulty, the procedures in this chapter should help to locate it. 

The stability of a chemical sensor is usually subject to a significant aging process. In the course of aging most sensors lose some of their selectivity, sensitivity, and stability. Some sensors, like the glass pH electrode, can be rejuvenated, while... 

This rejuvenating procedure will reduce the electrode life by making the glass bulb thinner or cracking the glass. Therefore, it should be used only after other methods of rejuvenation have failed to restore the electrode span or response. 

TTie return of used electrodes is ineffective and raises safety concerns from contamination of the wetted surfaces. It may be impossible to eliminate hazardous chemicals trapped in a porous junction. Also, the washing of the electrodes gets rid of coatings and rejuvenates the glass surface, which severely reduces the scope of the troubleshooting possible by the electrode manufacturer. Most electrode troubleshooting is best done onsite. 

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