FIG. 3.

Absorbance as a function of light wavelength and collagen concentration for paired hydroxyproline assays using Ehrlich's solution made with HClO₄ (A, C, E) or HCl (B, D, F). Marked nonspecific absorption occurred at wavelengths <500 nm and negligible absorption occurred at wavelengths >600 nm (A, B). Both solutions produced peak absorption and absorption:background ratios at wavelengths of 560–565 nm (C, D). The maximum absorption and absorption:background was less for Ehrlich's solution made from HCl, but both solutions produced a linear absorption response for concentrations of collagen between 1.25 and 20 μg/100 μL for wavelengths between 545 and 575 nm (E, F).