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Naturally occurring dissolved humic materials were fractionated according to molecular weight by dialysis and gel permeation chromatography. Components of higher molecular weight (>3,500) absorbed strongly at 250 nm but fluoresced weakly, while humic fractions of lower molecular weight fluoresced intensely per unit absorbance. With appropriate precautions, fluorescence: absorbance ratios may be useful in delineating seasonal and depth distribution patterns of dissolved humic materials of low and high molecular weight.
Stewart et al. (Thu,) studied this question.