Specific Determination of Trace Amount of Iron in Different Oxidation States in Coastal Sea Water to Investigate the Sources of Sea Desert

2007 Fiscal Year Final Research Report Summary

• Project/Area Number: 18550067
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Analytical chemistry
• Research Institution: Niigata University
• Principal Investigator: MATSUOKA Shiro Niigata University, Institute of Humanities, Social Sciences and Education, Associate Professor (10219404)
• Co-Investigator(Kenkyū-buntansha): YOSHIMURA Kazuhisa Kyushu University, Graduate School of Science, Professor (80112291)
• Project Period (FY): 2006 – 2007
• Keywords: coastal sea water / trace amount of iron / speciation / solid phase spectrometry / sea desert / on-site analysis

Research Abstract

Recently "sea desert" has been widely observed in the coastal region in Japan. One of the source of this sea desert is considered to be the decrease of the iron complex with organic compounds which is supplied from the soil to coastal sea water through rivers. However, the reliable data which can be applied to discuss on the source of sea desert have not been well reported because of the difficulty in determining the concentrations of trace amounts of iron in different oxidation state present in coastal sea water. In this study we have developed the high sensitive and selective speciation method using solid phase spectrometry for ultra trace iron in coastal sea waters to investigate the causes of sea desert which gives serious damages to inshore fisheries in Japan. The results obtained by this project are listed below.
1) The complex of [Fe(phen)3]2+ was strongly adsorbed on cation-exchange resin phase. The distribution ratio was in the 104 order and it was not affected by the ionic strength of sample solutions.
2) By using a small lens attached on the light detector window of a spectrophotometer, scattered light at the surface of ion-exchange resin beads could be effectively collected and focused at the light detector windows. This greatly reduced the back ground light attenuance of solid phase and made it possible to measure the light absorption of solid phase even at 1 cm light path length.
3) One of the features of the proposed method is that the proportional increases of sensitivity can be easily attained by the increase in the sample volume at a constant sold phase volume. In the case of using 0.25 g ion-exchange resin, the sensitivity could be increased by increasing the sample volume at least up to 400 cm3. The detection limit was 10 ng dm-3 when using 400 cm3 sample solutions.
4) Recovery test was also applied and good recoveries around 100% were obtained.