“Adwa buffer solutions are prepared according to precise formulas and standardised with a pH meter calibrated to NIST standards. All pH solutions are labelled with the batch number, expiry date and pH-temperature correlation table. This buffer solution is widely used in water treatment plants, the food industry and wherever pH is expected to be slightly acidic.
All pH electrodes must be calibrated from time to time. To perform a two-point calibration, follow the step-by-step procedure described below. A pH buffer of 6,86 and a pH buffer of 4,01 are required.
1) Wash the electrode thoroughly with distilled water to remove all traces of storage solution, process medium or previous test solution. Wash the electrode thoroughly after each buffer test to avoid transfer of contamination from pH buffers. Gently dry the electrode with a soft cloth to remove excess rinse water. Do not rub the bulb as this may cause static charge build-up.
2) Place the electrode and the A.T.C. (automatic temperature compensator) in pH 6,86 buffer solution. Allow 30 seconds for the electrode and/or A.T.C. to reach thermal equilibrium with the buffer solution. Adjust the pH meter to a pH reading of 6,86 using the standardisation/zero control.
Note: If the meter does not have an A.T.C., place a thermometer in the pH 6,86 buffer solution with the electrode. Allow 30 seconds for the pair to reach thermal equilibrium with the buffer solution. Adjust the temperature dial on the meter to match the thermometer reading. Then adjust the pH meter using the standardisation/zero control to give a pH reading of 6,86.
3) Repeat step 1 and place the electrode and A.T.C. in 4,01 buffer. Wait 30 seconds before adjusting the pH meter with the slope/distance control to give a pH reading of 4,01.
4) Repeat steps 2 and 3 for the most accurate calibration.
NOTES
a) For the most accurate results, always use fresh pH buffer solutions.
(b) In step 3, pH 10,01 buffer may be used instead of pH 4,01 buffer. All pH buffers above pH 6,86 are less stable and have a limited shelf life. These high pH buffers absorb CO2 from the atmosphere more readily and tend to change to a lower pH value when left open. For this reason, it is recommended to use a buffer solution of 4,01 to perform a reliable two-point calibration. In addition, the buffers should be within the desired pH range.
(c) When the pH electrode is calibrated with an automatic calibration meter, the required calibration procedure shall be specified in the instruction manual of the meter.
