I know this information is specific to my probe but thought it might prove useful in regards to this thread.
"The GK733526B electrode is rated for use from 0 - 100 °C. That does not mean is should be continuously used at that kind of elevated temperature, but if you are doing grab samples, it should not be a problem.
Accuracy should not be affected if you are using it at an elevated temperature, but you should be using a temperature sensor on your pH meter for accuracy at those temperatures, and yes, for most accuracy, you should also have your calibration standards at 68 °C when calibrating.
Also, do not expect to see the same pH readings at 68C as you do at 25C. I am not sure how your sample will respond to that kind of temperature change, but as an example, the pH 4 calibration buffer that reads 4.005 at 25C will read 4.116 at 70C; the pH 7 buffer that reads 7.000 at 25C will read 6.982 at 70C.
If you have any other questions, please let me know.