Sequential injection analysis for automation of the Winkler methodology, with real-time SIMPLEX optimization and shipboard application

Burkhard Horstkotte, Antonio Tovar Sánchez, Carlos Duarte, Víctor Cerdà*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

A multipurpose analyzer system based on sequential injection analysis (SIA) for the determination of dissolved oxygen (DO) in seawater is presented. Three operation modes were established and successfully applied onboard during a research cruise in the Southern ocean: 1st, in-line execution of the entire Winkler method including precipitation of manganese (II) hydroxide, fixation of DO, precipitate dissolution by confluent acidification, and spectrophotometric quantification of the generated iodine/tri-iodide (I2/I3-), 2nd, spectrophotometric quantification of I2/I3- in samples prepared according the classical Winkler protocol, and 3rd, accurate batch-wise titration of I2/I3- with thiosulfate using one syringe pump of the analyzer as automatic burette. In the first mode, the zone stacking principle was applied to achieve high dispersion of the reagent solutions in the sample zone. Spectrophotometric detection was done at the isobestic wavelength 466 nm of I2/I3-. Highly reduced consumption of reagents and sample compared to the classical Winkler protocol, linear response up to 16 mg L-1 DO, and an injection frequency of 30 per hour were achieved. It is noteworthy that for the offline protocol, sample metering and quantification with a potentiometric titrator lasts in general over 5 min without counting sample fixation, incubation, and glassware cleaning. The modified SIMPLEX methodology was used for the simultaneous optimization of four volumetric and two chemical variables. Vertex calculation and consequent application including in-line preparation of one reagent was carried out in real-time using the software AutoAnalysis. The analytical system featured high signal stability, robustness, and a repeatability of 3% RSD (1st mode) and 0.8% (2nd mode) during shipboard application.

Original languageEnglish (US)
Pages (from-to)147-155
Number of pages9
JournalAnalytica Chimica Acta
Volume658
Issue number2
DOIs
StatePublished - Jan 25 2010

Keywords

  • AutoAnalysis
  • Dissolved oxygen
  • Modified SIMPLEX method
  • Seawater monitoring
  • Sequential injection analysis
  • Winkler protocol

ASJC Scopus subject areas

  • Analytical Chemistry
  • Biochemistry
  • Environmental Chemistry
  • Spectroscopy

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