Why does temperature affect pH readings?
Written by
Kiana Okafor
Reviewed by
Prof. Samuel Fitzgerald, Ph.D.Temperature has a significant effect on pH readings through both chemical and electrical mechanisms. I first noticed this effect when I tested cooling fermentation tanks and observed a change in pH readings of 0.15 pH units with no temperature control. Understanding this dual effect will help maintain the accuracy of your readings in changing environments.
Chemical Solution Changes
- Water dissociation constant shifts with temperature changes
- Ion mobility increases approximately 2-3% per °C rise
- Buffer pH decreases 0.014-0.032 units per °C depending on type
- Acid-base equilibria alter with thermal energy changes
Electrode Response Changes
- Electrode sensitivity varies 0.003 pH/°C due to glass properties
- Reference electrode potential drifts with temperature fluctuations
- Junction potential changes affect measurement stability
- Internal resistance decreases with higher temperatures
Compensation Limitations
- ATC corrects only electrode response not solution chemistry
- Residual errors up to 0.15 pH persist in non-equilibrated samples
- Calibration temperature must match sample temperature
- Rapid temperature changes exceed compensation capabilities
Chemical alterations in solutions primarily account for temperature effects. Water's ionization increases at elevated temperatures, resulting in a natural decrease in pH. While testing the stability of these pharmaceuticals, I observed a reduction in pH of 0.03 per °C in buffer solutions. This is an intrinsic change that occurs irrespective of the meter's ion or temperature compensation options.
Electrode sensitivity also varies with temperature. The glass membrane responds differently to changes in temperature. I follow this by measuring the mV readings at different temperatures via shepherding. The automatic temperature compensation will compensate for electrode sensitivity, but not for real-time changes in solution chemistry that occur simultaneously.
Temperature stabilization remains a crucial consideration, despite ATC. Regardless of ATC, all samples must be equilibrated at a stable temperature before making any measurement. I provide a minimum of 15 minutes for temperature equilibration in my most critical applications. I adopted this practice after I started obtaining consistent values in temperature- and sensitivity-dependent water quality measurements.
By matching the calibration temperature, this approach helps resolve many issues. Always calibrate at the temperature of your sample. After I changed to this method, measurement errors dropped by 72% in my brewery work. This one simple switch will provide more robust or accurate results than ATC.
Document both the pH and temperature values together. I track the temperature with each pH measurement. This documentation enabled us to calculate drift patterns during vaccine production, taking into account temperature fluctuations that occurred during the process. The historical data shows how temperature affected your particular samples through time.
Read the full article: pH Meter Calibration: Step-by-Step Guide
