Glass bulb rejuvenation

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... 

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. 

Rejuvenation of the glass bulb will often provide faster response. This is accomplished by soaking the bulb in a solvent which will remove the coating or film. Any solvent may be used as long as it is also removed and the last soaking is in an aqueous-acidic solution. The choice of solvent or rejuvenating solution would depend on the most likely contaminate. In other words, in what samples has the glass bulb been immersed and in what solvents is... 

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. 

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. 

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