3.4 Data analysis
It is assumed that the interaction between hemin (H) and
antimalarial drug (Q) can be described according to the equilibrium shown
below:
(3-2)
In diluted solutions, the association constant of
complex K can be written as follows:
 (3-3)
and
where  is the concentration of complex and  and  are the initial concentrations of hemin and drug, respectively
(3-4)
(3-5)
Combining Equations (3-2), (3-3), (3-4) and (3-5), the
resulting quadratic equation can be written as:
 (3-6)
One of the roots of the equation (3-6) is given by:
 (3-7)
The optical absorption of the system during titration can be
written as:
 (3-8)
where A and d are the optical density and
the light path, respectively,  and  are the molar extinction coefficients of hemin and its complex
solutions.
Combining Equations (3-4) and (3-7), with Equation (3-8), the
following equation is obtained:
 (3-9)
Where A0 is the molar extinction of hemin
solution at  =0, and ( =  - ) is the difference of the molar extinction coefficients between
hemin complex and free hemin. The basic data are initial concentrations of
hemin ( ) and drug ( ) and the corresponding optical absorption of hemin (A). With these
data, parameters particularly the equilibrium constant K, can be
fitted according to Eq. (3-9) with the help of Microsoft Origin 6.1 package.
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