Flow Injection With Chemiluminescence Detection For The Determination Of Iron In Surface Atlantic Waters

Abstract

This thesis describes the design, optimisation and shipboard deployment of a flow injection -chemiluminescence (FI-CL) technique for the determination of iron (Fe) in seawater. ChapterOne presents an overview of the marine biogeochemistry of Fe, including its speciation, sourcesand sinks, abundance and limitation for phytoplankton growth in the Wodd*s oceans. Currentanalytical methods for the determination of Fe in natural waters are also reviewed.Chapter Two reports the instrumental development of the FI - CL method. Each component isdescribed and its suitability to the flow manifold discussed. Different CL detection systems areevaluated and a charge coupled device used to investigate the spectral profile of the Fe-catalysedluminol reaction. Automation of the FI manifold is also detailed along with acquisition of CLsignals. Chapter Three details the optimisation of a FI - CL procedure for the determination ofFe in seawater. Reagent clean-up techniques, blank procedures and a standard additionoperating routine are detailed. Fe(III) reduction using sulphite is treated theoretically. Matrixeffects are investigated and the synthesis of an 8-hydroxyquinoline resin used for in-line matrixelimination and preconcentration is reported. The optimised method is selective to Fe(II+IIl)in the linear range 0.04-10 nM, with a precision of 3.2% (n=5) for a LO nM standard and a limitof detection (3s) of 40 pM for a load time of 1 min. Chapter Four presents the results of aninvestigation into the kinetic effect of Fe on luminol CL using the continuous addition ofreagent (CAR) technique. Instrumental and chemical parameters are optimised, interferencesinvestigated and the CAR-CL technique compared with alternative flow configurations.In Chapter Five, the application of the F - CL method to the shipboard determination of Fe inthe surface North and South Atlantic (SO'^N to 50°S) is presented. Data are reported for samplescollected from the upper water column (<200 m) in eight different biogeochemical provinces,which represent coastal, upwelling and oligotrophic regions of the Adbntic Ocean. Totaldissolvable iron (unfiltered, TD-Fe) levels range ftom <0.1 to 6.1 nM and indicate that high andspatially variable TD-Fe (>2 nM) concentrations exist in Equatorial and tropical North Atlanticregions influenced by atmospheric deposition from the West African continent. Away fromstrong input mechanisms, TD-Fe concentrations in the upper water column average 0.6 nM.Input sources are fingerprinted via correlation with other trace metals (Al, Co, Ni), nutrients andhydrography, whilst active biological uptake is shown to be the dominant sink. TD-Fe verticaldistributions through the upper mixed layer display strong relationships with chlorophyll aconcentrations, and measurements in the deep chlorophyll maximum of the South Atlanticoligotrophic gyre show that, despite elevated nitrate at such depths, Fe concentrations are at aminimum (ca. 0.1 nM) and may be low enough to (co-)limit phytoplankton growth.

Date of Award	1999
Original language	English
Awarding Institution	University of Plymouth