LimsPulse
Titration & electrochemistry

pH meter

Measures how acidic or alkaline a solution is by measuring the small voltage produced by a glass electrode. Used for pH of products, buffers, mobile phases and water.

  • Pharmaceutical
  • Biotech
  • Food & beverage
  • Water treatment
  • Chemicals
  • Environmental
Photo of a pH meter
Photo: Datamax, Public domain (cropped), via Wikimedia Commons
Follow your site SOP
This is a typical operating sequence for learning. Your instrument model and approved SOP take precedence.
STAGE 1

Before you start

  1. 1Check the meter's calibration status and the electrode's condition (no cracks, electrolyte filled to the mark, no crystals at the junction).
  2. 2Open the refill hole during measurement so electrolyte flows freely through the junction.
  3. 3Let buffers and samples reach the measuring temperature (commonly 25 ± 2 °C, or as defined in the method).
  • Never let the glass bulb dry out. Store it in storage solution, not in purified water.
STAGE 2

Calibration

  1. 1Use at least two fresh buffers that bracket the expected sample pH (for example pH 4.01 and 7.00 for an acidic sample).
  2. 2Rinse the electrode with purified water and blot gently with a lint-free tissue; do not wipe the bulb.
  3. 3Immerse in the first buffer (usually pH 7.00), stir gently and accept the value when stable.
  4. 4Rinse and repeat with the second (and third) buffer.
  5. 5Check the slope and offset shown by the meter, then read a check buffer as described in your SOP.
  • Never pour used buffer back into the bottle. Discard buffer after use and observe the buffer's expiry date.
STAGE 3

Measuring samples

  1. 1Rinse the electrode and immerse it in the sample so the bulb and junction are covered.
  2. 2Stir at the same gentle rate used for calibration.
  3. 3Record the pH and temperature when the reading is stable (for example a change of less than 0.02 pH in 30 seconds, or as your SOP defines).
  4. 4Rinse the electrode between samples.
  • If the sample pH falls outside the calibrated range, recalibrate with buffers that bracket it.
STAGE 4

After use

  1. 1Rinse the electrode, close the refill hole and place it in storage solution.
  2. 2Record the use in the instrument log.
In LimsPulse · Calibration Management

Keep every pH meter in control: usage logs, calibration and maintenance schedules, and automatic blocking of overdue instruments.

See how