Specifications

3. Operation MI 611-211 – October 2005
23
have a default of 0.0. The values (VALx) can be specified from -2.00 to +16.00 pH and have a
default of 0.00.
If the average pH values of two special buffers are less than 1 pH unit apart, using this procedure
might result in the wrong buffer being selected. In this case, the buffer selection is based on the
midpoint between the two buffers. It is not necessary to configure all three special buffers. If only
two are used, they should be Buffers 1 and 2. If one is used, it should be Buffer 1. Enter Special
buffer tables in the increasing order of the average pH for the buffer. The average pH is estimated
as (first entry + last entry) / 2.
Tables of buffer values for nominal 4, 7, and 10 pH for American, NIST, and European buffers
are listed below:
NOTE
Values in Table 7 are based on common (nominal value) technical buffer systems.
pH values are at 25°C. Chemical formulas are as follows:
4.00 pH: 0.05 molar Potassium Hydrogen Phthalate
7.00 pH: 0.041 molar Disodium Hydrogen Phosphate;
0.026 molar Potassium Dihydrogen Phosphate
10.01 pH: 0.025 molar Sodium Carbonate;
0.025 molar Sodium Bicarbonate
Table 7. American Buffer Tables
Temperature
°
C
4.00 pH 7.00 pH 10.01 pH
pH Value pH Value pH Value
0 4.00 7.12 10.32
5 4.00 7.09 10.25
10 4.00 7.06 10.18
15 4.00 7.04 10.12
20 4.00 7.02 10.06
25 4.00 7.00 10.01
30 4.01 6.99 9.97
35 4.02 6.99 9.93
40 4.03 6.98 9.89
45 4.04 6.98 9.86
50 4.06 6.97 9.83
Table 8. NIST Buffer Tables
Temperature
°
C
4.01 pH 6.86 pH 9.18 pH
pH Value pH Value pH Value
0 4.00 6.98 9.46
5 4.00 6.95 9.40
10 4.00 6.92 9.33