User Guide
Instruction Manual pH 510/ Ion 510
25
8 ADDITIONAL INFORMATION
8.1 pH and Temperature
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 solutions and the sample
solution the same.
8.2 Use of Standard pH Buffers
Use standard buffer solutions to calibrate a pH meter before you measure the pH of a sample. They serve as
reference standards for basis of comparison between measurement. The most common USA standard buffers
are the pH 4.01, pH 7.00 and pH 10.01 and the NIST standard buffers are pH 4.01, pH 6.86 and pH 9.18. 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-point calibration when the sample pH is completely unknown. Use all pH 7.00, pH 4.01 and pH
10.01 calibration solutions.
8.3 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 calibration value may be different from the buffer value at 25
o
C.
USA Buffer NIST Buffer
Temperature (
o
C)
pH 4.01 pH 7.00 pH 10.01 pH 4.01 pH 6.86 pH 9.18
0 4.01 7.12 10.32 4.01 6.98 9.47
5 4.01 7.09 10.25 4.01 6.95 9.38
10 4.00 7.06 10.18 4.00 6.92 9.32
15 4.00 7.04 10.12 4.00 6.90 9.27
20 4.00 7.02 10.06 4.00 6.88 9.22
25 4.01 7.00 10.01 4.01 6.86 9.18
30 4.01 6.99 9.97 4.01 6.85 9.14
35 4.02 6.98 9.93 4.02 6.84 9.10
40 4.03 6.97 9.89 4.03 6.84 9.07
45 4.04 6.97 9.86 4.04 6.83 9.04
50 4.06 6.97 9.83 4.06 6.83 9.01
55 4.08 6.97 9.81 4.08 6.83 8.99
60 4.10 6.98 9.79 4.10 6.84 8.96
70 4.12 6.99 9.76 4.12 6.85 8.92
80 4.16 7.00 9.74 4.16 6.86 8.89
90 4.20 7.02 9.73 4.20 6.88 8.85