Molecular characterization of organic nitrogen in cattle manure compost by size-exclusion HPLC with chemiluminescent nitrogen detection.

To characterize organic nitrogen present in cattle manure compost, a hot-water extract of the compost along with an acid-insoluble (humic acid-like) fraction either treated with alkali or laccase or untreated were separated by size-exclusion high-performance liquid chromatography (SE-HPLC). Nitrogen was then detected by chemiluminescent nitrogen detection (CLND), and humic acid-like substances were detected by measuring the absorbance at 420 nm. The acid-insoluble fraction comprised the higher molecular-weight region in the chromatogram of the whole extract, and its chromatogram pattern of CLND was similar to that of the absorbance at 420 nm. Changes in the molecular-weight distribution of the acid-insoluble fraction detected by CLND due to alkaline degradation and laccase polymerization were in agreement with those observed by measuring the absorbance at 420 nm. These results, together with other data, demonstrate that protein and humic acid-like moieties are present in the same molecule in compost organic matter.