title: Liquid waveguide spectrophotometric measurement of nanomolar ammonium in seawater based on the indophenol reaction with o-phenylphenol (OPP).
abstract: We describe a highly sensitive colorimetric method for the determination of nanomolar concentrations of ammonium in seawater based on the indophenol reaction with o-phenylphenol [(1,1'-biphenyl)-2-ol, abbreviated as OPP]. OPP is available as non-toxic, stable flaky crystals with no caustic odor and has some advantages over phenol in practical use. The method was established by using a gas-segmented continuous flow analyzer equipped with two types of long path liquid waveguide capillary cell, LWCCs (100 cm and 200 cm) and an UltraPath (200 cm), which have inner diameters of 0.55 mm and 2 mm, respectively. The reagent concentrations, flow rates of the pumping tubes, and reaction path and temperature were determined on the basis of a manual indophenol blue method with OPP (Kanda, Water Res. 29 (1995) 2746-2750). The sample mixed with reagents that form indophenol blue dye was measured at 670 nm. Aged subtropical surface water was used as a blank, a matrix of standards, and the carrier. The detection limits of the analytical systems with a 100 cm LWCC, a 200 cm LWCC, and a 200 cm UltraPath were 6, 4, and 4 nM, respectively. These systems had high precision (<4% at 100 nM) and a linear dynamic range up to 200 nM. Non-linear baseline drift did not occur when using the UltraPath system. This is due to the elimination of cell clogging because of the larger inner diameter of the UltraPath compared to the LWCCs. The UltraPath system is thus more suitable for long-term measurements compared with the LWCC systems. The results of the proposed sensitive colorimetry and a conventional colorimetry for the determination of seawater samples showed no significant difference. The proposed analytical systems were applied to underway surface monitoring and vertical observation in the oligotrophic South Pacific.
authors.affiliation: Department of Ocean Sciences, Tokyo University of Marine Science and Technology, Konan, Minato, Tokyo 108-8477, Japan. Electronic address: f-hashi@kaiyodai.ac.jp.
authors.forename: Fuminori
authors.initials: F
authors.lastname: Hashihama
authors.affiliation: Department of Ocean Sciences, Tokyo University of Marine Science and Technology, Konan, Minato, Tokyo 108-8477, Japan.
authors.forename: Jota
authors.initials: J
authors.lastname: Kanda
authors.affiliation: Department of Ocean Sciences, Tokyo University of Marine Science and Technology, Konan, Minato, Tokyo 108-8477, Japan.
authors.forename: Ami
authors.initials: A
authors.lastname: Tauchi
authors.affiliation: Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, University of Tokyo, Yayoi, Bunkyo, Tokyo 113-8657, Japan.
authors.forename: Taketoshi
authors.initials: T
authors.lastname: Kodama
authors.affiliation: Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8564, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Saito
authors.affiliation: Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, University of Tokyo, Yayoi, Bunkyo, Tokyo 113-8657, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Furuya
mesh_terms: D064751:Ammonium Compounds / Q000032:analysis* / Q000737:chemistry; D001713:Biphenyl Compounds / Q000737:chemistry*; D007215:Indophenol / Q000737:chemistry*; D012623:Seawater / Q000032:analysis*; D013053:Spectrophotometry / Q000379:methods
chemical_list: D064751:Ammonium Compounds; D001713:Biphenyl Compounds; D007215:Indophenol; C004369:2-phenylphenol
keywords: Ammonium; Colorimetry; Liquid waveguide capillary cell; Seawater; o-Phenylphenol