Additional Information; Ph And Temperature; Use Of Standard Ph Buffers; Standard Ph Buffers - Fisher Scientific accumet AE150 User Manual

Additional Information

pH and Temperature

Automatic Temperature Compensation (ATC) compensates for temperature changes. Some
solutions show an increase in pH while others show a decrease in pH with the same
temperature change. Always record the solution temperature along with the pH value when
taking measurements. Temperature changes also affect the signal the pH electrode sends to
the meter and cause a loss of accuracy for the reading if they are not accounted for. To limit
the loss of accuracy during calibration, ensure the temperature of the pH buffer solutions and
the sample solutions are the same.

Use of Standard pH Buffers

Use standard buffer solutions to calibrate a pH meter before measuring the pH of a sample.
They serve as reference standards for basis of comparison between measurements. The
most common USA standard buffers are the pH 1.68, 4.01, 7.00, 10.01 and 12.45 buffers
and NIST standard buffers are pH 1.68, 4.01, 6.86, 9.18 and 12.45 buffers. For one point
calibration, use a standard buffer of pH 7.00 or pH 6.86. Use two 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 three to five point calibration when the sample pH is unknown.

Standard pH Buffers

The following table shows pH buffer values at various temperatures during calibration. The
table also illustrates why a calibration value may be different from the buffer value at 25 °C.
Temp. (°C) 1.68 4.01
0 1.67 4.01
5 1.67 4.01
10 1.67 4.01
15 1.67 4.00
20 1.68 4.00
25 1.68 4.01
30 1.69 4.01
35 1.69 4.02
40 1.70 4.03
45 1.70 4.04
50 1.71 4.06
55 1.72 4.08
60 1.73 4.10
65 1.73 4.11
70 1.74 4.12
75 1.75 4.14
80 1.77 4.16
85 1.78 4.18
90 1.80 4.23
95 1.81 4.23
100 1.81 4.23
25 of 28
USA pH Buffer
7.00 10.01 12.45
7.12 10.32 13.43
7.09 10.25 13.21
7.06 10.18 13.00
7.04 10.12 12.81
7.02 10.06 12.63
7.00 10.01 12.45
6.99 9.97 12.29
6.98 9.93 12.13
6.97 9.89 11.99
6.97 9.86 11.84
6.97 9.83 11.70
6.97 9.81 11.58
6.98 9.79 11.45
6.98 9.77 11.45
6.99 9.76 11.45
6.99 9.75 11.45
7.00 9.74 11.45
7.01 9.73 11.45
7.02 9.73 11.45
7.03 9.74 11.45
7.03 9.74 11.45
accumet AE150 pH Benchtop Meter
Temp. (°C) 1.68
0 1.67
5 1.67
10 1.67
15 1.67
20 1.68
25 1.68
30 1.69
35 1.69
40 1.70
45 1.70
50 1.71
55 1.72
60 1.73
65 1.73
70 1.74
75 1.75
80 1.77
85 1.78
90 1.80
95 1.81
100 1.81
NIST pH Buffer
4.01 6.86 9.18 12.45
4.01 6.98 9.46 13.43
4.01 6.95 9.40 13.21
4.01 6.92 9.33 13.00
4.00 6.90 9.28 12.81
4.00 6.87 9.23 12.63
4.01 6.86 9.18 12.45
4.01 6.85 9.14 12.29
4.02 6.84 9.11 12.13
4.03 6.84 9.07 11.99
4.04 6.83 9.04 11.84
4.06 6.83 9.01 11.70
4.08 6.83 8.99 11.58
4.10 6.84 8.96 11.45
4.11 6.84 8.94 11.45
4.12 6.85 8.92 11.45
4.14 6.85 8.91 11.45
4.16 6.86 8.89 11.45
4.18 6.87 8.87 11.45
4.23 6.88 8.85 11.45
4.23 6.88 8.85 11.45
4.23 6.88 8.85 11.45
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