Procedure:


Step 1- Remove the electrode from its short term storage solution.

Step 2- Rinse the electrode with distilled water (A). Tap off the residual rinse water and blot the electrode dry with a kimwipe or lint free cloth (B).

Step 3- Expose the fill hole by removing the fill hole plug.

Step 4- Verify that the fill solution is not more than one inch (2.5 cm) from the fill hole. If additional fill solution is needed go to Step 5. If the fill solution is within one inch of the fill hole go to Step 6.

Step 5- Using a transfer pipet, add fill solution until the level is within one inch of the fill hole. Not all pH electrodes require the same fill solution. The correct fill solution must be used for the electrode to function properly. Check the owners manual to verify what the correct fill solution for your electrode is.

Step 6- Place the electrode in a pH 7.00 buffer solution (A and B). Press the calibration button on the pH meter (C). Wait for the buffer value to appear on the meter display (D).

Step 7- Remove the electrode from the buffer (A). Rinse the electrode thoroughly with distilled water (B). Blot the electrode dry with a kimwipe or a lint free cloth (C).

Step 8- Place the electrode in a pH 4.00 buffer solution (A and B). Press the calibration button on the pH meter (C). Wait for the buffer value to appear on the meter display (D).

Step 9- Remove the electrode from the buffer (A). Rinse the electrode thoroughly with distilled water (B). Blot the electrode dry with a kimwipe or a lint free cloth (C).

Step 10- Place the electrode in a room temperature, representative portion of the sample being measured (A). Press the read button on the meter (B). Wait for the pH value to lock onto the meter screen (C). Note that the actual sample temperature is also displayed. Record the sample pH.

Step 11- Remove the electrode from the sample. Rinse the electrode completely off using distilled water. For viscous samples it may be necessary to rinse the bulk of the sample off using tap water, and then rinse with distilled water. This step is critical to ensure other samples and buffer solutions are not contaminated with residual product clinging to the electrode. Blot the electrode dry with a kimwipe or lint free cloth.

Step 12- Repeat Step 8 through Step 11 for each additional measurement made. Continue to Step 13 when all samples have been measured.

Step 13- Close the fill hole by replacing the fill hole plug.

Step 14- Replace the electrode into the short term storage solution.

Note:

• pH standards are based upon room temperature samples. The pH of a sample may vary significantly depending upon temperature. An ATC (automatic temperature compensator) will not correct for the specific product temperature variation. An ATC is built to compensate for the electrode performance variations due to temperature, and is not able to compensate for the sample variations. For this reason it is necessary for samples to be as close to room temperature (25 C) when measurements are made.
• pH meters have a certain degree of complexity. It is not possible to write a generalized procedure for all meters. This test procedure is specifically designed to aid Food QA Lab employees in using the CORNING pH meter 340. It is not meant to replace necessary training by qualified personnel. If you have any questions concerning the measuring of pH, seek assistance in your work until you are comfortable with the procedure. For detailed questions concerning the pH electrode and meter, refer to the appropriate manual.

Food QA Lab Home