Figure 2. UV-visible absorption spectra showing the Soret band as a function of pH; (a)molar absorptivity of Hcc solutions; (b) absorbance of supernatant solutions of Hcc sorbed on hematite. Because the concentration of Hcc in the supernatant solutions was based on molar absorptivity in solutions, the molar absorptivity of the supernatant solutions could not be compared independently.