This study introduces the concept of consistent examination of changes of log-transformed absorbance spectra of dissolved organic matter (DOM) at incrementally increasing concentrations of heavy metal cations such as copper, cadmium, and aluminum at environmentally relevant concentrations. The approach is designed to highlight contributions of low-intensity absorbance features that appear to be especially sensitive to \DOM\ reactions. In accord with this approach, log-transformed absorbance spectra of fractions of \DOM\ from the Suwannee River were acquired at varying pHs and concentrations of copper, cadmium, and aluminum. These log-transformed spectra were processed using the differential approach and used to examine the nature of the observed changes of \DOM\ absorbance and correlate them with the extent of Me-DOM complexation. Two alternative parameters, namely the change of the spectral slope in the range of wavelengths 325–375 nm (DSlope325–375) and differential logarithm of \DOM\ absorbance at 350 nm (DLnA350) were introduced to quantify Cu(II), Cd(II), and Al(III) binding onto DOMs. \DLnA350\ and DSlope325–375 datasets were compared with the amount of DOM-bound Cu(II), Cd(II), and Al(III) estimated based on NICA-Donnan model calculations. This examination showed that the \DLnA350\ and DSlope325–375 acquired at various pH values, metal ions concentrations, and \DOM\ types were strongly and unambiguously correlated with the concentration of DOM-bound metal ions. The obtained experimental results and their interpretation indicate that the introduced DSlope325–375 and \DLnA35\ parameters are predictive of and can be used to quantify in situ metal ions interactions with DOMs. The presented approach can be used to gain more information about DOM-metal interactions and for further optimization of existing formal models of metal-DOM complexation.