Determination of sub-nanomolar levels of iron in seawater using flow injection with chemiluminescence detection

The development of a highly sensitive system for the shipboard determination of dissolved iron at the sub-nM level is presented. The technique is based on a flow injection method coupled with luminol chemiluminescence detection. Dissolved Fe(II+III) levels are determined after Fe(III) reduction using sulphite and in-line matrix elimination/preconcentration on an 8-hydroxyquinoline (8-quinolinol) chelating resin column. The detection limit (3s) is 40 pM when 1.5 ml of sample is loaded onto the column, and the relative standard deviation is 3.2% (n=5) for a 1.0 nM Fe sample. One analytical cycle can be completed in 3 min. The automated method proved reliable when employed on-board the RRS James Clark Ross during Autumn 1996, mapping dissolvable Fe(II+III) levels along the Atlantic Meridional Transect from 50°N to 50°S. Data from vertical profiles through the upper water column are presented.