General Aspects of Two-Wavelength Methods

The determination of the optical density of a two-component system at wavelengths Xi and provides two equations  

The total concentration of light-absorbing substances c is introduced, and c — C2 is substituted for Ci. If, furthermore, X2 is an isobestic wavelength, then These conditions being fulfilled, Eq. (8) may be 

The concentration of component 2 is now expressed as a fraction of the total pigment concentration, and the equation is solved for c /c  

The constants a and b in Eq. (9) can be calculated from a series of measurements of of solutions containing exclusively component 1 or com- 

Equation (9) is of the form y = Ax + B, the relationship between 02/0 and thus being linear. Knowing two points only, it is therefore 

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