Netherlands Polar Data Center

Dissolved iron was measured directly on board by Flow Injection Analysis (FIA) after De Jong et al. 1998 in a cleanroom container. In a continuous FIA system the acidified pH 1.8, filtered (0.2µm) seawater is buffered to pH 4.0. The iron is concentrated on a column which contains the column material aminodiacetid acid (IDA). This material binds only transition metals and not the interfering salts. After washing of the column with ultra pure water (MQ) the column is eluted with diluted acid. After mixing with luminol, peroxide and ammonium the oxidation of luminal with peroxide is catalysed by iron and a blue light is produced and detected with a photon counter. The amount of iron is calculated using a standard calibration line, where a known amount of iron is added to low iron containing seawater. Using this calibration line a number of counts per nM iron is obtained. A total of 795 samples, divided over 42 stations are measured. All samples have been analyzed on board. The values of Fe measured varied from below 0.1 -10 nM. The standard deviation varied between 0% and 8% (exceptional), but was generally lower than 5%. The standard deviation of the values is determined of a triplicate measurement of the same sample bottle. To correct for contamination during the process or in the sample bottle a duplicate sample was taken of every station depth. The intra-daily consistency of the system was verified using a drift standard. Regularly a certified SAFe standard (Johnson et al. 2007) for the long term consistency and absolute accuracy was measured.