Quality control/assurance assignment

SOP of calibration of a pH meter

Calibration and adjustment

These should always be performed after: switching on the pH meter replacement of electrode checking the calibration and the deviation of the

pH from the theoretical value of the standard buffer appears to exceed 0.05 unit.

When the pH meter is on and already adjusted then only a check of the adjustment is needed (described in Section 7.1 of this SOP),

Calibration step 1Transfer sufficient standard buffer solution pH 7.00 to a

50 ml or 100 ml beaker. Measure temperature of buffer and set switch 14 (temp.

compensation) to this temperature. Immerse electrode in buffer solution and push button 4

(measure). With button 6 (Ucomp) adjust value on display (8) to

theoretical pH value of the buffer at the measured temperature. (Note: this value can be read from a table enclosed with the standard ampoule).

Push button 3 (stand-by). Rinse electrode with water. Setting of switch 6 (Ucomp) should now not be changed any more

Calibration step 2Transfer a sufficient volume of one of the two other

buffer solutions (pH 4 or 9) to a 50 ml or 100 ml beaker. (Note: this second buffer is chosen such that the pH of the solution to be measured falls in between , the first and second calibration buffer).

Measure temperature of buffer and adjust switch 14 (temp. compensation) to this temperature.

Immerse electrode in buffer solution and push button 4 (measure),

With switch 13 (slope) adjust the value on the display to the theoretical pH value of this buffer. (Note: this value can be read from a table enclosed with the standard ampoule).

Calibration step 2The setting of switch 13 may not be lower than 0.95. If this condition is not met, this electrode may not be used for the measurement and must be exchanged for another one which does meet the condition.

Push button 3 (stand-by) and rinse electrode with water.

As a check, repeat readings of buffers (pH 7 first) and readjust according to Step 1 and 2 if necessary.

Reference: http://www.fao.org/docrep/W7295E/

w7295e07.htm#app%20071%20%20%20operation%20of%20ph%20meter%20metrohm%20e%20632