title: A portable analyser for the measurement of ammonium in marine waters.
abstract: A portable ammonium analyser was developed and used to measure in situ ammonium in the marine environment. The analyser incorporates an improved LED photodiode-based fluorescence detector (LPFD). This system is more sensitive and considerably smaller than previous systems and incorporates a pre-filtering subsystem enabling measurements in turbid, sediment-laden waters. Over the typical range for ammonium in marine waters (0–10 mM), the response is linear (r(2) = 0.9930) with a limit of detection (S/N ratio > 3) of 10 nM. The working range for marine waters is 0.05–10 mM. Repeatability is 0.3% (n =10) at an ammonium level of 2 mM. Results from automated operation in 15 min cycles over 16 days had good overall precision (RSD = 3%, n = 660). The system was field tested at three shallow South Florida sites. Diurnal cycles and possibly a tidal influence were expressed in the concentration variability observed.
authors.affiliation: Cooperative Institute for Marine and Atmospheric Studies (CIMAS), Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, USA. natchanon.amornthammarong@noaa.gov
authors.forename: Natchanon
authors.initials: N
authors.lastname: Amornthammarong
authors.forename: Jia-Zhong
authors.initials: JZ
authors.lastname: Zhang
authors.forename: Peter B
authors.initials: PB
authors.lastname: Ortner
authors.forename: Jack
authors.initials: J
authors.lastname: Stamates
authors.forename: Michael
authors.initials: M
authors.lastname: Shoemaker
authors.forename: Michael W
authors.initials: MW
authors.lastname: Kindel
mesh_terms: D004784:Environmental Monitoring / Q000191:economics / Q000295:instrumentation*; D004867:Equipment Design; D005470:Fluorometry / Q000191:economics / Q000295:instrumentation*; D005618:Fresh Water / Q000032:analysis*; D000644:Quaternary Ammonium Compounds / Q000032:analysis*; D012623:Seawater / Q000032:analysis*; D012680:Sensitivity and Specificity
chemical_list: D000644:Quaternary Ammonium Compounds