title: Fluorometric determination of ammonium ion by ion chromatography using postcolumn derivatization with o-phthaldialdehyde.
abstract: A postcolumn fluorometric derivatization method for the determination of trace amounts of ammonium ion (microg/L level) under matrices with high concentrations of sodium and amino acids has been developed. In this method, ammonium ion was determined by ion chromatography combined with fluorometric detection (IC-FL) in less than 16 min. IC was performed in a high-capacity cation-exchange Dionex IonPac CS16 analytical column (250 mm x 5 mm) under isocratic conditions with 30 mM methanesulfonic acid (MSA) as mobile phase at flow-rate 1.0 mL/min. To remove amino acid interference, the postcolumn derivatization based on the reaction of ammonia with o-phthaldialdehyde (OPA) and sulfite was applied. The excitation and emission wavelengths were 364 and 425 nm, respectively. The effects of pH, reaction temperature and time, OPA-reagent composition and concentration, and sample matrix were studied. The linear range and detection limit of this method were similar to the standard method. The IC-FL method with a postcolumn fluorometric derivatization allows the routine determination of ammonium ion in extreme matrices where the ratios of sodium and amino acids to ammonium are up to 2,800,000:1 and 28,000:1, respectively.
authors.affiliation: Environmental Chemistry Laboratory, Department of Atomic Science, National Tsing Hua University, 101, Sec. 2, Kuang Fu Road, Hsinchu 30013, Taiwan.
authors.forename: Chun-Ting
authors.initials: CT
authors.lastname: Kuo
authors.forename: Po-Yen
authors.initials: PY
authors.lastname: Wang
authors.forename: Chien-Hou
authors.initials: CH
authors.lastname: Wu
mesh_terms: D002852:Chromatography, Ion Exchange / Q000295:instrumentation / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D000644:Quaternary Ammonium Compounds / Q000032:analysis* / Q000737:chemistry; D012623:Seawater / Q000737:chemistry; D013050:Spectrometry, Fluorescence / Q000379:methods*; D013447:Sulfites / Q000737:chemistry; D013696:Temperature; D009764:o-Phthalaldehyde / Q000737:chemistry*
chemical_list: D000644:Quaternary Ammonium Compounds; D013447:Sulfites; D009764:o-Phthalaldehyde; C025026:sodium sulfite