Enzyme-Linked Immunosorbent Assay for Humic Acids

An enzyme-linked immunoassay (ELISA) for the determination of humic acid in natural-water samples was developed. For antisera production, humic acid was coupled to helix pomatia hemocyanin. A humic acid-horseradish peroxidase conjugate was synthesized as a tracer. The detection limit of this competitive assay was estimated to be 0.5 μ/1, which means 100 pg absolute. The cross-reactivities at the center point (50%-value) of several commercial humic acids and both aliphatic and aromatic acids were determined. Moreover, the structural aspects of the humic acids could be elucidated.