Biomedical Engineering Reference
In-Depth Information
Fig. 7.2.
Buffer capacity (titration curve; this example: addition of acid)
for 0.05-M Tris buffer (pK
Tris
= 8.06)
I: ionic strength; c
i
:concentrationofioni;z
i
: Charge of ion i; n:
number of ion species within the solution.
Taking ionic strength into consideration, the modified dissoci-
ation constant pK
may be calculated by the Debye-Hückel rela-
tionship:
A
I
·
√
I
1+
√
I
pK
=
pK + (2z
i
−1)
·
−c
i
·
The term A is a temperature-dependent constant. Values of A be-
tween 0 and 60
◦
C aregiveninTable7.3.
Since electrolytes, especially weak electrolytes, are not com-
pletely dissociated at higher concentrations, the degree of dissoci-
ation
α
i
of an ion has to be introduced into calculations (theoreti-
cally, a salt is totally dissociated at infinite dilution, i.e., at infinite
Table 7.3.
Values of constant A at different temperatures
◦
C
A
0
0.4918
10
0.4989
20
0.5070
25
0.5114
30
0.5161
37
0.5321
40
0.5262
50
0.5373
60
0.5494
