Shipboard techniques based on flow injection analysis for measuring dissolved Fe, Mn and Al in seawater

An overview is presented of sampling techniques and flow injection analysis (FIA) methods for low concentrations of Fe, Mn and Al in filtered seawater . On the basis of sampling procedures, filtration techniques, accuracy, bla nks, detection limits, intercalibration results and oceanographic consisten cy, the feasibility of these FIA methods was evaluated. It was found that t hese metals could be measured on board with a minimum risk of contamination and with good accuracy even at low subnanomolar levels (< 0.5 nM). Results for reference seawater were in the case of Fe-FIA and Mn-FIA in excellent agreement with the certified values. Data from samples analyzed by Fe-FIA a nd by cathodic stripping voltametry (CSV) compared well, as did Mn-FIA and GFAAS. All three methods gave results that were mostly in good agreement wi th data from the same ocean regions published by other research groups. Two different types of surface water sampling were also tested and compared, n amely conventional hand filling of a sample bottle from a rubber dinghy awa y from the ship, and underway pumping of seawater using a 'tow fish'. The l atter method gave the best results. Also, conventional membrane filtration and cartridge filtration for large volume filtration were compared using Fe and Al data from water column samples. Good agreement was found for both f ilter types, although for defining dissolved metal species the latter filte r type was preferred.