DETERMINATION OF SUBNANOMOLAR LEVELS OF IRON(II) AND TOTAL DISSOLVED IRON IN SEAWATER BY FLOW-INJECTION ANALYSIS WITH CHEMILUMINESCENCE DETECTION

A highly sensitive technique for the rapid determination of Fe(II) and total dissolved iron in seawater has been developed. The technique employs flow injection analysis and chemiluminescence detection (FIA-CL). The light is emitted by the reaction of brilliant sulfoflavin with hydrogen peroxide and Fe(II) in a neutral medium. A cation-exchange column is used to preconcentrate the iron from seawater. The detection limit was 0.45 nmol/L when 4.4 mL of sample was passed through the column. Lower detection limits are attainable with larger sample volumes. The relative standard deviation is 2-5% for concentrations greater than 2.5 nmol/L. A typical analysis can be performed in 5 min. The technique was determined to be accurate based on the analysis of the trace metal standard seawater solutions NASS and CASS. Shipboard analyses provided oceanographically consistent profiles for total iron and also revealed some of the first profiles for Fe(II) in hydrothermal plume samples. A typical profile of 12 samples, together with blanks and standards, can be analyzed in triplicate in 4.5 h.