Real-Time Detection of Dissolved Free Amino Acids and Ammonium in Seawater

摘要

Dissolved free amino acids (DFAAs) and ammonium are important nutrients in marine microbial food webs. DFAA concentrations are most often studied by high-pressure liquid chromatography of fluorescent derivatives with o-phthaldialdehyde (OPA). This procedure is laborious, requires extensive sample handling, and yields results hours or days after sampling. A fluorescent monitoring system for DFAAs, other primary organic amines, and ammonium was developed that is automated and continuous, and provides results in real-time. A gently pumped stream of seawater is reacted with an OPA/mercaptoethanol/buffer reagent and passed under the tip of a fiber optic probe supplying excitation light below 400 nm. The fluorescent signal, with a maximum at 455 nm, is transmitted by the probe to an optical multichannel analyzer employing a linear photodiode array. A plot of fluorescent intensity vs. time is recorded. The signal is linear in the range 1 to 100 nM alanine equivalents.