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

近年来，日本沿海地区普遍出现了“海漠”现象。这种海洋沙漠的来源之一被认为是铁络合物与有机化合物的减少，这些化合物从土壤中通过河流提供给沿海海水。然而，由于难以确定沿海海水中不同氧化态的微量铁的浓度，尚无可靠的数据可用于讨论海漠的来源。本研究采用固相光谱法对日本近岸海域超痕量铁进行了高灵敏度、高选择性的物种分析，探讨了对日本近岸渔业造成严重危害的海漠成因。本项目取得的成果如下：1) [Fe(phen)3]2+配合物在阳离子交换树脂相上被强吸附。分布比为104数量级，且不受样品溶液离子强度的影响。2)利用附着在分光光度计的光探测器窗口上的小透镜，可以有效地收集离子交换树脂珠表面的散射光，并将其聚焦在光探测器窗口上。这大大降低了固相的背景光衰减，使得在光路长度为1cm时测量固相的光吸收成为可能。3)该方法的一个特点是，在一定的销售相体积下，样品体积的增加可以很容易地实现灵敏度的比例增加。在使用0.25 g离子交换树脂的情况下，可以通过将样品体积增加至少400 cm3来提高灵敏度。当使用400 cm3样品溶液时，检出限为10 ng dm-3。4)进行了回收率试验，回收率在100%左右。

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.