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)