Photochemical behavior of Fe(II) in coastal seawater around Okinawa Island by HPLC with a Ferrozine reagent

Abstract

We studied the total dissolved iron concentrations and photochemical formation of Fe(II) in coastal seawater samples collected around Okinawa Island by using a Ferrozine (FZ) reagent. The total dissolved iron concentrations were the highest at sites receiving large river water. Red-soil polluted sites showed a higher total dissolved iron concentration than clean seawater sites, indicating the impacts of red soil. Fe(II) was studied by high-performance liquid chromatography using the FZ reagent (FZ-HPLC). We improved the reported FZ-HPLC method by adopting Poly Ether Ether Ketone (PEEK) materials to the instruments and joint tubing to minimize contamination from the analytical instrument. We also used a suction needle adopter so as to prevent the stainless-steel needle from contacting the injected solutions. The photochemical behavior of Fe(II) was studied by using a solar simulator, and the Fe(II) kinetics was roughly divided into three types. Type A was that the Fe(II) concentrations were almost constant during the irradiation experiments. Type B was that the Fe(II) concentrations increased for the 0 to 5 minutes of irradiation, and gradually decreased after that. Type C was that the Fe(II) concentrations increased with the irradiation time until it reached a plateau. It was inferred that the photoformation of Fe(II) was strongly affected by the dissolved Fe(III) concentrations, dissolved organic compounds, and salinity. It should be noted that since the Fe(II) concentrations were not zero at the beginning of the photochemical experiments, it became evident that oxidation-resistant Fe(II) species existed in the coastal seawater samples collected around Okinawa Island. © 2005 The Japan Society for Analytical Chemistry.