Continuous shipboard determination of Fe(II) in polar waters using flow injection analysis with chemiluminescence detection Original Research Article

A method for the continuous underway determination of Fe(II) in polar waters is reported. Surface seawater is pumped into a shipboard clean room container using a towed fish with Teflon diaphragm pump. Fe(II) was determined by flow injection analysis using a modified FeLume. The seawater is filtered in-line and the sample containing Fe(II) is mixed with luminol (buffered to pH 10) inside a flow cell and the resulting luminescence signal measured by a Hamamatsu HC-135 photon counter linked to a laptop computer. No preconcentration of the samples was applied, to reduce possible interferences and increase the sampling frequency. The system was utilised during EISENEX, a meso-scale iron enrichment experiment sample in the Atlantic sector of the Southern Ocean. In EISENEX, when surveying the iron enriched patch, a sample was analysed every 110 s (60 s loading time and 50 s for analysis). The detection limit, as determined by analysis of seawater (maintained at 4 °C to minimise oxidation) spiked with known concentrations of Fe(II), ranged from 25 to 133 pM. The system was also applied to vertical profiles of Fe(II) during EISENEX.