Improved speciation of dissolved organic nitrogen in natural waters: amide hydrolysis with fluorescence derivatization.

The objective of this study was to improve primary-amine nitrogen (1 degree-N) quantification in dissolved organic matter (DOM) originating from natural waters where inorganic forms of N, which may cause analytical interference, are commonly encountered. Efforts were targeted at elucidating organic-N structural criteria influencing the response of organic amines to known colorimetric and fluorescent reagents and exploring the use of divalent metal-assisted amide hydrolysis in combination with fluorescence analyses. We found that reaction of o-phthaldialdehyde (OPA) with primary amines is significantly influenced by steric factors, whereas fluorescamine (FLU) lacks sensitivity to steric factors and allows for the detection of a larger suite of organic amines, including di- and tri-peptides and sterically hindered 1degree-N.