How to calibrate pH electrodes?

How to calibrate pH electrodes?

pH Electrode Calibration

• For accurate, repeatable pH measurements, all pH electrodes must be calibrated periodically.

• Two-point, three-point, and five-point calibration procedures characterize an electrode with a particular pH meter.

• Once an electrode is characterized the electrode-meter pair can be used to find out the pH of a solution.

• When a pH sensor is placed in a solution, whose pH is to be measured, an electrochemical reaction takes place. A low voltage (mV) signal is generated and measured by the probe to the analyzer/transmitter.

• The potential difference between the reference electrode and measurement electrode is pH. In combination electrodes, both reference electrode and measuring electrode are available in one body. Whereas, other electrode belong to two separate electrode.

• Internally, the analyzer takes all output of the electrode which it measures and draw a curve according to that, and finds the slop (mV) of it.

• All the buffer solution have their own specific mV which mention the backside of the solution. Generally, calibration can be processed with a pH of 4.0 1, 7.00, 9.21. solution. It completely depends on which type of calibration method is used for it.

• The basic model of the pH has 2 point calibration or 3 point calibration, and the advanced model of the pH model has 5 point calibration. It has more accurate than another one.

• The analyzer calculates the slop for all measured values. If the slop comes between range which has already set by the manufactured, we can say that electrode working found perfectly.

• The analyzer also does the relay activation or current output. The relay outputs can be used to operate pumps, 4-20 mA for the regulation of valves in pH control.

Electrode Care

• pH electrodes must be calibrated periodically at certain intervals.

• Whenever a replacement pH probe is connected to an analyzer, it must be calibrated before use. Every pH sensor should be calibrated to ensure accurate, repeatable readings. Recalibration should also be done at regular intervals.

• For the best accuracy, the sensor(s) and analyzer should be calibrated together.

• Always use fresh buffers, as high pH buffers are prone to absorbing atmospheric CO2. Perform the calibration shortly after filling the beaker with buffer.

• Using the auto-calibration procedure the analyzer automatically recognizes the buffers and uses temperature-corrected pH values in the calibration. All the time, due to process conditions, auto-calibration is not possible.

Two-point Calibration

• The step-by-step procedure is described below to perform a two-point calibration on the pH electrode.

• A 7.00 pH and a 4.00 pH buffer solution are required.

Step 1:

• Rinse the electrode thoroughly in de-mineralized (DM) water beaker to remove all traces of the previous test solution.

Note:

• Thoroughly rinse the electrode after each buffer test to prevent carry-over traces of contamination of the pH buffer solutions. Gently clean the electrode on soft tissue to remove the excess rinse water.

• Rinse the electrode and the automatic temperature compensator (ATC) in a 7.00 pH buffer solution.

• Allow 30 seconds for the electrode/ATC to reach thermal equilibrium and stable reading with the buffer solution.

• Adjust the pH meter with the standardized/Zero control for a pH indication equal to 7.00.

Step 2:

• Repeat Step 1 and insert the electrode and the ATC in a 4.00 buffer solution.

• Allow 30 seconds for reading to get stabilized before adjusting the pH meter with the slope/span control for a pH indicator equal to 4.00.

Step 3:

• Repeat Steps 1 and 2 to improve the precision of the calibration.

• Do not rub the bulb since it can cause damage to the electrode bulb or even cause a static charge build-up.