1. An analytical method, comprising: injecting into a flow analysis system a known volume of each of a plurality of analytical samples, each sample comprising a dihydric phenol and a monohydric phenol; detecting the absorbance of the known volume of each analytical sample at at least two wavelength ranges; and determining the concentration of the dihydric phenol in each analytical sample based on the absorbance of the known volume of each analytical sample at at least two wavelength ranges; wherein the method has a total analysis time not greater than about 5 minutes per sample.