title: A reverse-flow injection analysis method for the determination of dissolved oxygen in fresh and marine waters.
abstract: A reverse flow injection method (rFIA) based on the Winkler titration chemistry, is reported for the determination of dissolved oxygen (DO) in natural waters. Manganese(II) sulfate is injected into a continuously flowing stream of sample and subsequently merges with a reagent stream of sodium hydroxide and sodium iodide. Manganese(II) hydroxide that is formed reacts with DO in the sample to form an oxidized manganese hydroxyoxide floc. Addition of 10% sulfuric acid dissolves this floc, and under acidic conditions, the triiodide ion formed is detected by photometry in a flow through cell at a wavelength of 440 nm. The method is rapid (48 measurements per h), repeatable (R.S.D. ca. 3%, n=3), and has a calculated detection limit of 0.25 mg l(-1) (P=0.001). No interference from nitrite or ferrous ions was observed at concentrations typically found in natural waters. The method has been successfully applied to on-line measurement of DO in sediment respiration reactors.
authors.affiliation: Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand.
authors.forename: Saowapha
authors.initials: S
authors.lastname: Muangkaew
authors.forename: Ian D
authors.initials: ID
authors.lastname: McKelvie
authors.forename: Michael R
authors.initials: MR
authors.lastname: Grace
authors.forename: Mongkon
authors.initials: M
authors.lastname: Rayanakorn
authors.forename: Kate
authors.initials: K
authors.lastname: Grudpan
authors.forename: Jaroon
authors.initials: J
authors.lastname: Jakmunee
authors.forename: Duangjai
authors.initials: D
authors.lastname: Nacapricha