The task of obtaining the solution with a certain value of the activity (or equilibrium
concentration) of one of the components and regulating their equilibrium composition is directly
related to the creation of buffer systems. The possibility of fine regulation of the composition of
buffer systems is based on their insensibility to small disturbances - routing errors. A high
buffering capacity leads to a more stable and secure regulating the equilibrium concentrations.
Thus, for example, by using buffer systems, the influence of adsorption and other external
factors on pIon can be excluded. Buffers are also used as reference standards and tests of the
pIon scale by means of ion selective electrodes. The ionic buffers are generally called such
systems, which are able to maintain constant the equilibrium concentration (or activity) of one of
ions.
In this paper, the expressions for calculating the buffer capacity towards the metal ion
and ligand in the systems, in which the complex formation reactions take place, have been
derived and the correlation between these functions has been found. The obtained results for a
number of specific systems correlate well with known experimental data. The obtained relations
can be used to create new buffers of investigated type. For practical use it is necessary such
buffers, in which the equilibrium concentration of ligand is small and independent of the solution
pH. These requirements are accomplished by such buffer systems, which besides the main metal
ion and ligand, contain a second metal. The set of possible equilibria in the buffer systems of
second type has been examined:
Here M is the main metal ion, N presents the second metal ion and L is ligand.
For this system, the following expressions for calculating buffer capacities have been
derived:
, (1)
, (2)
In the equations (1)-(2) through Ci the total concentration of the component “i” in solution is
denoted and Ai are various concentration functions. One can observe from the equations (1) and
(2) that some important reciprocal relations exist between the quantities.
The obtained relations allow: (1) the exact calculation of buffer capacities of the
homogeneous systems towards both the activities of the metal ions and ligand on the basis of the
respective thermodynamic equilibrium constants; (2) a more complete disclosure of the
mechanism of the buffer action of ionic buffer systems; (3) search and create new perspective
buffers. The validity of the derived equations has been confirmed by correlation of the existing
experimental evidence with the calculated data obtained in this paper.