46
Standard pH Buffers
The following table shows the various pH values at different temperature
of the solution during calibration. The table also illustrates why a calibra-
tion value may be different from the buffer value at 25°C.
Temperature
pH buffer values
°C
°F
4.01
7.00
10.00
(phthalate)
(neutral
(carbonate)
phosphate)
0
32
4.01
7.12
10.33
5
41
4.01
7.09
10.25
10
50
4.00
7.06
10.18
15
59
4.00
7.04
10.11
20
68
4.00
7.02
10.05
25
77
4.01
7.00
10.00
30
86
4.01
6.99
9.95
35
95
4.02
6.98
9.92
40
104
4.03
6.98
9.88
45
113
4.04
6.97
9.85
50
122
4.06
6.97
9.82
55
131
4.07
6.98
9.80
60
140
4.09
6.98
9.77
70
158
4.12
6.99
9.73
80
176
4.16
7.00
9.69
90
194
4.20
7.02
9.66
Appendix 3: pH and temperature
pH and Temperature
The pH electrode is affected by temperature changes. Automatic Temperature Compensation
(ATC) compensates for temperature changes. Some solutions show an increase while others a
decrease in pH with the same temperature change. Record the solution temperature along with
the pH value, or the measurement may be meaningless. Temperature changes also affect the
signal the pH electrode sends to the meter and causes a loss of accuracy for the reading. To limit
the loss of accuracy during calibration, make the temperature of the pH buffer calibrating solu-
tions and the sample solution the same.
pH Buffer Calibration Solution
Use standard buffer solutions to calibrate a pH meter before you measure the pH of a sample.
Calibration solutions serve as basis of comparison between measurements. The most common
standard buffers are the pH 4.01, pH 7.00 and pH 10.01, but this meter can let you calibrate as
many as 5 points for highest accuracy over the entire range, or at very low or high pH levels.
For 1-point calibration, use a standard buffer of pH 7.00 or a standard buffer whose pH value is
close to that of the sample. Use 2-point calibration when you know the sample is acidic (low pH)
or basic (high pH). For acidic samples, use standard buffers of pH 7.00 and pH 4.01. For basic
samples, use standards of pH 7.00 and pH 10.01. Use a 3 (or more) point calibration when the
sample pH is completely unknown.
Contact your OAKTON
®
distributor for information on pH buffer and calibration solutions.
troubleshooting
electrode
care
measurement
calibration
starting up
set up
mode
return of
items
warranty
accessories
specifications
appendixes
