Table 1.

Extinction coefficients of the blue and purple complexes at various wavelengths

Wavelength, nm	Extinction coefficient, mM−1⋅cm−1
	Purple complex*	Blue complex†
562	27.9	8.94
600	12.1	12.1
635	3.8	15.3
700	<0.2	6.1

^*The extinction coefficients of the purple complex at the various wavelengths were determined by direct measurement of the absorbances of solutions containing a known concentration of Fe(II) and a 5-fold molar excess of Fz. It is assumed that under these conditions all of the Fe(II) will be converted to the purple complex. These values are identical to those that have been previously determined (7–9) for an authentic sample of the Ferrozine–iron complex, Fz₃Fe(II). 

^† The extinction coefficients of the blue compound at the various wavelengths are calculated values based on the assumption that the difference spectrum of the His–Fz–Fe(II) complex (heavy broken line, Fig. 2E) is the same as that of the purple complex (12.1 mM⁻¹⋅cm⁻¹) at the isosbestic point of 600 nm.