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What to do when your pH meter does not measure pH properly

PH Meter
PH Meter

pH meters are wonderful devices until they go wrong. You are then left with your sample sitting on the bench and in some instances, not knowing what is wrong. The following questions and answers are designed to help you diagnose the problem.

My pH meter won’t give a fixed reading – is drifting or providing erratic readings?

  • Contaminated sensing glass — Blockages of the sensing glass at the base of the electrode will reduce the ability of the electrode to correctly conduct. Therefore, results in sporadic changes to the reading obtained. Always make sure you clean you electrode correctly on a regular basis making sure to remove all the contamination on the glass. We provide a number of electrode cleaning solutions for this purpose.
  • Clogged junction — Be especially vigilant in cleaning after using semi-solid samples. These have a tendency to leave sediment on the electrode. An additional aspect to consider is when using samples with a high protein concentration. Make sure to use an enzyme-based cleaning solution to digest the protein. Should clogging be a recurring issue, when measuring semi-solid or viscous samples, you may need to consider using a pH electrode.  This should have an open junction design.
  • Low conductivity samples — for such samples use an electrode that has a high junction flow rate. Or, add high purity potassium chloride (KCl) to increase conductivity.
  • Electrode improperly hydrated — To prevent this store correctly in a storage solution designed for this purpose making sure to clean prior to storage.
  • Electrical noise interference — This can interfere with electrical machinery, including pH meters. Try and read a sample away from the interference if possible.

My pH readings are incorrect – varying constantly or just showing the same reading. What is causing this?

  • Wiping the electrode — Wiping or rubbing the electrode has a tendency to cause a number of issues. These include – static electricity building up on the electrode, removal of the hydration layer on the electrode bulb and scratching of the electrode surface. Ideally, not wiping the electrode will be best, but, if removal of liquid from the electrode bulb is required, be sure to blot not wipe with a lint-free paper towel.
  • Incorrect calibration — One key factor when recording calibration points is to make sure the pH electrode is rinsed with distilled water between calibration buffers. This prevents cross-contamination. Be sure to use fresh buffers for each calibration should you notice an error or issue with the buffers. pH calibration buffers will change over time and therefore need to be replaced, check the instruction and replace accordingly.
  • Temperature-related issues — When reading a sample make sure that calibration and sample readings are done at the same temperature. Alternatively, use a pH meter with automatic temperature compensation. Always check the temperature charts on calibration buffers and set the pH to the appropriate pH value for the temperature.
  • Cracked electrode — When the reading is the same whatever the solution used. Check the type of pH electrode you need before ordering.

For further information and advice please contact support@camlab.co.uk. Alternatively, visit our website. Here you can find a range of pH meters and electrodes, along with all the necessary pH electrode buffers, cleaning solutions, filling solutions and storage solutions.