pH meters employing a glass electrode are
useful for precise pH measurement in nutrient solutions but require frequent calibration, proper
storage and handling to ensure accuracy and reliability. The principle on
which such meters operate is based on the fact that when glass of a
certain composition separates 2 aqueous solutions having different
hydrogen ion concentrations, a voltage is developed between the two faces
of the glass. The electronic meter itself is simply a very sensitive
voltmeter which measures that voltage but is calibrated in terms of pH
units instead of volts.
Obtaining pH readings
Step 1. Make sure the meter is
calibrated.
Step 2. Remove a ‘representative’
sample from the nutrient reservoir:
+ Stir the nutrient thoroughly prior to
sampling.
+ Ensure the sampling container is clean.
Step 3. Rinse electrode in distilled
water before immersing in the sample. Wait a few minutes** before
switching the meter on and recording the pH.
** Wait longer if the sample’s temperature
is significantly different from 25oC (77oF).
Step 4. If the pH is not between
5.0 and 6.5, adjust it
immediately.
Step 5. When complete, rinse
electrode with distilled water. Store the electrode in a proper
storage solution when
not in use.
