Resolving Analytical Differences in the Determination of Iron in Seawater

Targeting Colloidal and Organically-complexed Iron Species

Supervisors

Andrew Bowie (UTas), Paul Haddad (UTas)

Project Outline

Suitable for graduates with degrees in Chemistry (preferably Analytical), with a focus towards Oceanography/Marine Science or Earth/Environmental Science disciplines. A strong interest in the biogeochemistry of trace elements in the ocean would be desirable. Students should meet normal University PhD entry requirements.

Background and rationale

The element iron is thought to have a controlling effect on phytoplankton growth and species composition in more than 40% of the World's oceans, including the climatically-important, high-nutrient low-chlorophyll Southern Ocean [1]. This importance of iron for marine phytoplankton production and carbon transport through the ocean requires that it is measured routinely and accurately during oceanographic field studies. Iron has a complex and reactive chemistry at the extremely low concentrations (1.0 nmol L^-1) present in seawater, existing in two redox states and in a variety of inorganic and organic complexes, and colloids. Recent studies show that serious discrepancies exist in iron concentrations determined by the 10 or more different analytical methods used worldwide [2-4]. These discrepancies are believed to be due to the lability of organic and colloidal iron species (which account for 80-99% of the dissolved iron existing in seawater) to extraction by adsorbent preconcentration resins that are used upstream in most analytical techniques [5].

Methodology

In this project, the student will initially study a range of iron species in seawater in model colloids, suspended particles, synthetic ligands and natural organic compounds (both independently and as complex mixtures), in order to evaluate the ability of the existing adsorbent resin materials to quantitatively recover these fractions. Dissolved iron determinations will be performed using a method based on flow injection analysis (FIA) with chemiluminescence detection [6], with in-line analyte preconcentration and seawater matrix elimination achieved using a resin microcolumn containing immobilised 8-hydroxyquinoline [5]. This technique is sensitive (limits of detection in the pmol L^-1 range), rapid, minimises the risk of sample contamination and operable on-board research vessels, and has been used in recent field programs of the Antarctic Climate & Ecosystems CRC.

To begin with, methods will be validated against archived Southern Ocean seawater samples. As the project develops, a series of novel functionalised resins will be synthesised and adsorbent properties characterised for the selective extraction of different physico-chemical iron species that exist in seawater. Through careful choice of pre-treatment and extraction steps, the methods will be developed in order to specifically include or exclude such colloidal and organically-bound iron leading to species-specific analytical techniques. In years 2 and 3, the student will have the opportunity to deploy the newly-developed methods on oceanographic cruises in the Southern Ocean, and to collaborate with and visit researchers from other international laboratories that are actively involved with the measurement of dissolved iron in seawater.

Wider implications

This work will significantly improve our understanding of the bioavailability of iron (and other bioactive trace elements) in the ocean and lead to the generation of class-specific analytical methodologies. The project will also progress a current Scientific Committee for Oceanographic Research (SCOR) - National Science Foundation (NSF) initiative [7] towards the certification of iron in seawater, and help lead to the routine production of certified reference materials suitable for trace iron determinations in seawater.

Training

The successful applicant will join an active team within the University of Tasmania, the Antarctic Climate & Ecosystems CRC and CSIRO Marine Research that is working on important aspects of trace elemental biogeochemistry in the Southern Ocean. The student will be trained in state of the art ultra-clean analytical procedures for use both at sea and on land. Further development of sampling procedures will be made as required for low-level trace metal analysis. The successful candidate will also participate in a student focused seminar series, and receive additional training from the Research Higher Degrees Unit at the University in the range of skills required for a successful postgraduate career.

Note: due to the availability of instrumentation, this project would suit a mid-2005 start date.

References

[1] Moore J. K., Doney S. C., Glover D. M., Fung I. Y. (2002). Iron cycling and nutrient-limitation patterns in surface waters of the World Ocean. Deep-Sea Research II 49, 463-507.

[2] Bowie A.R., Achterberg E.P., Blain S., Boye M., Croot P.L., Laan P., Sarthou G., de Baar H.J.W., Worsfold P.J. (2003). Shipboard analytical intercomparison of dissolved iron in surface waters along a north-south transect of the Atlantic Ocean. Marine Chemistry 84, 19-34.

[3] Bowie A.R., Sedwick P.N., Worsfold P.J. (2004). Analytical intercomparison between flow injection-chemiluminescence and flow injection-spectrophotometry for the determination of picomolar concentrations of iron in seawater. Limnology and Oceanography: Methods 2, 42-54

[4] Measures C.I., Vink S. (2001). Dissolved Fe in the upper waters of the Pacific sector of the Southern Ocean. Deep-Sea Research II 48, 3913-3941.

[5] Landing, W.M., Haraldsson, C., Paxeus, N. (1986). Vinyl polymer agglomerate based transition metal cation chelating ion-exchange resin containing the 8-hydroxyquinoline functional group. Analytical Chemistry 58, 3031-3035.

[6] Bowie A.R., Achterberg E.P., Mantoura R.F.C., Worsfold P.J. (1998). Determination of sub-nanomolar levels of iron in seawater using flow injection with chemiluminescence detection. Analytical Chimica Acta 361, 189-200.

[7] Johnson K.S. et al. (2003). SAFe: Sampling and Analysis of Iron: an international collaboration. Project funded by the National Science Foundation for oceanographic fieldwork in the North Pacific in October-November 2004.

Contact

Dr Andrew Bowie or tel +61 3 6226 2509 or +61 3 6226 7656