Follow the procedures recommended by the manufacturer. Properly working electrodes commonly drift from about 0.1 to 0.2 mV per hour. Follow manufacturer's instructions. Deterioration of the electrode is normal, and proper maintenance requires that electrode performance be monitored before every water-quality field trip and again at each site. Oily film or scratches on the bulb will interfere with pH measurement.
Fingers leave a protein film on the glass that decreases electrode sensitivity.
Cut, frayed, or broken cable. Bent or broken connector. Rinse electrode thoroughly with deionized water before use. Gently blot droplets from a wet glass electrode bulb with lens paper or soft tissue by contacting only the droplets to soak up excess solution. It can take many minutes for the electrode to return to normal operation.