Issues and Behavior of pH Meter

Asked by: naasuaysai On: October 13, 2014 Product Type: Cosmetics

Question

I have some questions about the behavior of my pH meter when measuring substances like serum. I've observed the following:

  1. When I turn the meter on without immersing it in any liquid, the reading is not 0. Why is this?
  2. The reading fluctuates (around 0.1-0.3 pH units) when my hands are near the meter or when someone walks by. Is this normal?
  3. When I immerse the meter in a liquid, the reading takes a long time to stabilize and may still drift slightly (around 0.1-0.2 pH units) even after leaving it for several minutes. Is this expected?
  4. I measured the pH of a serum, then refrigerated it, and measured it again. The pH changed significantly (by 1.0-1.5 pH units). Why does temperature affect the pH reading so much?

Answer

Subject: Regarding pH meter usage

Hello,

Based on the conversation, here's an explanation regarding the behavior of your pH meter:

  • Why the reading is not 0 when turned on: A pH meter measures the concentration of hydronium ions, which are present in the air. Therefore, the reading will not be zero when the meter is turned on.
  • Fluctuations when hands are near or walking by: It is normal for less expensive pH meters to show minor fluctuations (like 0.1-0.3 pH units) when there is movement or proximity. This can be due to static electricity, electromagnetic interference, or other environmental factors affecting the sensitive electrode.
  • Reading not stabilizing quickly: Inexpensive pH meters often take longer to stabilize, and the reading may continue to drift slightly (like 0.1-0.2 pH units) even after several minutes. The properties of the liquid being measured (like viscosity in a serum) can also affect stabilization time. High-quality meters are designed for faster and more stable readings.
  • Effect of temperature on pH: Temperature significantly affects pH readings. The pH of a solution changes with temperature because the ionization of water and the dissolved substances are temperature-dependent. Measuring at different temperatures, especially with a large difference like refrigerating and then measuring, will result in different pH values. It is standard practice to measure pH at a consistent temperature, often 20°C or 25°C, to ensure comparable results. A change of 1.0-1.5 pH units after refrigeration is a significant difference but can occur due to the large temperature change.
  • Conclusion: The behavior you described – minor fluctuations due to proximity/movement, slow stabilization, and significant change with temperature – is typical for entry-level or less expensive pH meters. For highly accurate and stable measurements, especially in professional settings, more expensive, higher-quality pH meters are required.

Hope this clarifies the behavior you are observing.

Tags

Accuracy Equipment Issue Stability Temperature Control pH Measurement