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

最近，在日本沿海地区广泛观察到“海洋沙漠”。这种海洋沙漠的来源之一被认为是减少了从土壤中通过河流提供给沿海海水的铁与有机化合物的络合物。然而，由于难以测定沿海海水中不同氧化态的痕量铁的浓度，因此，可用于讨论海洋沙漠来源的可靠数据尚未得到很好的报道。本研究发展了一种高灵敏度、高选择性的固相光谱法测定近海沃茨中超痕量铁的形态分析方法，以研究日本近海渔业遭受严重破坏的海洋荒漠化的原因。结果表明：1）[Fe（phen）_3]~（2+）在阳离子交换树脂上有较强的吸附。2）在分光光度计的光检测窗上安装一个小透镜，可以有效地收集离子交换树脂珠表面的散射光，并将其聚焦在光检测窗上。这大大降低了固相的背景光衰减，使得在1cm光路长度下也能测量固相的光吸收。3）所提出的方法的一个特点是，在固相体积不变的情况下，可以通过增加样品体积来容易地实现灵敏度的成比例增加。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高达400 cm 3来增加灵敏度。当使用400 cm ~ 3样品溶液时，检测限为10 ng dm ~（-3）。4）还进行了回收试验，回收率约为100%。

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.