1. Make sure your standard buffer solutions are in good condition (fresh and uncontaminated)
  2. Make sure your standard buffer solutions are at room temperature (close to 25˚C or 77˚F)
  3. Set the meter back to factory default setting (refer to your meter’s manual for operation)
  4. Insert the pH electrode to the following standard buffers – 7.00 pH, 4.00 pH, 10.01 pH (add 1.68 pH and 12.45 pH if necessary) – and record the readings (rinse out the electrode between tests).
  5. For example, you get the following readings in the buffers – 6.96 pH, 4.03 pH, 9.92 pH, 1.73 pH, 12.32 pH – Do the slope calculations as follows:
    • Slope in 7.00 to 4.00: (6.96-4.03)/(7.00-4.00)=97.67%
    • Slope in 7.00 to 10.01: (9.92-6.96)/(10.01-7.00)=98.34%
    • Slope in 4.00 to 1.68: (4.03-1.73)/(4.00-1.68)=99.14%
    • Slope in 10.01 to 12.45: (12.32-9.92)/(12.45-10.01)=98.36%
  6. If the temperature is far off from 25˚C or 77˚F, you would need to use the standard values based on the specific temperature according to the following chart:
Temperature
7.00 pH
4.00 pH
10.01 pH
1.68 pH
12.45 pH
5˚C/41˚F
7.09
4.00
10.25
1.67
13.23
10˚C/50˚F
7.06
4.00
10.18
1.67
13.01
15˚C/59˚F
7.04
4.00
10.12
1.67
12.81
20˚C/68˚F
7.02
4.00
10.06
1.68
12.62
25˚C/77˚F
7.00
4.00
10.01
1.68
12.45
30˚C/86˚F
6.99
4.01
9.97
1.68
12.27
35˚C/95˚F
6.98
4.02
9.93
1.69
12.11
40˚C/104˚F
6.97
4.03
9.89
1.69
11.96
45˚C/113˚F
6.97
4.04
9.86
1.70
11.83
50˚C/122˚F
6.96
4.06
9.83
1.71
11.70
55˚C/131˚F
6.96
4.07
9.81
1.72
11.58
60˚C/140˚F
6.97
4.09
9.78
1.72
11.47

 

For example, if the temperature of your buffers is at 15˚C/59˚F, the slope calculations are as follows (buffer readings are represented by T7, T4, T10, T1, T12):

  • Slope in 7.00 to 4.00: (T7-T4)/(7.04-4.00)
  • Slope in 7.00 to 10.01: (T10-T7)/(10.12-7.04)
  • Slope in 4.00 to 1.68: (T4-T1)/(4.00-1.67)
  • Slope in 10.01 to 12.45: (T12-T10)/(12.81-10.12)