A pH calibration is always performed before the pH-meter is used formeasurements. A calibration is a check that the pH-meter works as it should, and that it gives the expected pH readings when usingpH buffers. Before starting the calibration, be sure you are properly准备.
Normally 3 calibration points per calibration are used, and a flushing step in buffer before the actual reading, but this can be different in local procedures.
Steps for each calibration point
- Flush the pH electrode in distilled or higher quality of water.
- pH电极浸入第一个包含er with the relevant pH buffer.
- Immerse the pH electrode into the pH buffer so the diaphragm (usually a blue glass tip) is completely immersed.
- Make sure there are no bubbles surrounding the pH electrode.
- If specified in local procedures, use stirring.
- Wait until the reading on the pH meter is stable.
- When the reading is stable, wait approximately another 15 seconds.
- If the reading is still stable after the 15 seconds then continue
- Register the following:
- The reading of the pH meter
- The temperature
- Use the temperature to look up the table value of thepH buffer
Repeat the steps above for each calibration point. Thencalculate the error and evaluatethe calibration points, and finallyconclude on the calibrationas a whole. This might lead to that you cannot release the pH-meter, but need to take further action, so check out these sections. Remember to also date and sign the calibration documentation.
What is a stable reading
- Stable reading means that the value displayed on the pH meter is not systematically increasing or decreasing. This is also calleddrifting. The pH also should not change too much up and down, but some fluctuation on the last digit is okay.
- A stable reading always requires that the pH buffer, fixture and pH electrode. have approximately thesame temperature.
- For some pH buffers, e.g. buffer 4 and 7, the time before stability can be less that one minute. For other buffers, e.g. 1 and 12, the time before stability can often be more than one minute.