Concentration Variations of Trace Metals in Surface Seawater along the Ferry Track between Osaka and Okinawa as Determined by ICP-MS after Chelating Resin Preconcentration
Concentration Variations of Trace Metals in Surface Seawater along the Ferry Track between Osaka and Okinawa as Determined by ICP-MS after Chelating Resin Preconcentration
复制标题
螯合树脂预富集后 ICP-MS 测定大阪和冲绳之间渡轮航线表层海水中痕量金属的浓度变化
DOI：
10.2116/analsci.16.675
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发表时间：
2000
影响因子：
1.6
通讯作者：
H. Haraguchi
中科院分区：
文献类型：
--
作者：
T. Yabutani;Fumihiko Mouri;H. Haraguchi
极低，但往往反映了由于生物活动或某些人工来源的环境污染而导致水生环境的一些变化。因此，为了环境保护，非常需要监测沿海和开放海水中的痕量金属。然而，沿海和公海地区的海水采样通常是一项困难而乏味的工作。因此，在本实验中，在渡轮（黑潮丸；关西汽船，大阪）上安装了用于船上收集表层海水的自动采样系统，并于 1996 年 12 月 5 日至 7 日期间在大阪和那霸之间的渡轮轨道上的 17 个采样点采集了表层海水样品。1 通过螯合树脂后的 ICP-MS（电感耦合等离子体质谱法）测定了表层海水中的痕量金属浓度。预浓缩2 海水样品通过设置在船底的不锈钢管道在地表水以下5 m 处采集。虽然每个采样点的部分海水样品未经过滤，但采样后立即用膜过滤器（孔径0.45μm）过滤剩余的海水样品。这两个未过滤和过滤的样品均用硝酸酸化至 pH 1。然而，在本实验中，仅对经过过滤的样品进行了海水中溶解的痕量金属的总浓度的测定。高密度聚乙烯瓶用于样品保存。在 ICP-MS 测定之前，通过以下程序预浓缩海水样品中的痕量金属。2,3 首先，将 250 ml 海水样品放入烧杯中，并使用乙酸溶液和氨水溶液将样品的 pH 调节至 pH 6。然后，将0.2g（干重）购自BioRad Laboratories（Richmond，CA，USA）的螯合树脂（Chelex-100）添加到海水样品中，并用磁力搅拌器搅拌样品溶液2小时。用玻璃过滤器(G4)过滤海水样品，用8ml 1M乙酸铵溶液冲洗过滤器上的螯合树脂，以洗脱部分吸附在螯合树脂上的任何Mg和Ca。最后，用 6 ml 2 M HNO3 溶液洗脱吸附在螯合树脂上的所有分析物金属，并向其中添加 0.5 ml Ge、In、Re 和 Tl 的混合溶液（各 100 μg l–1）作为内标元素。结果，实现了体积约40倍的预浓缩。该解决方案作为 ICP-MS 测量的分析解决方案提供。本方法可测定约 25 种痕量金属，2 尽管以下讨论仅限于氧阴离子形成元素（V、Mo、W 和 U）、Cd 和 La。本实验中检查的分析物元素的分析检出限估计如下。4 首先，仪器检出限是作为与 3 倍空白信号强度在每个 m/z 的相对标准偏差 (3σ) 相对应的分析物元素浓度来获得的。 ICP-MS 测量，以 2 M HNO3 作为空白溶液。然后，根据仪器检出限计算分析检出限，同时考虑预富集因子和螯合树脂预富集中的回收率。 2 通过本分析方法获得的分析检出限为 V 0.001 μg l–1、Mo 0.002 μg l–1、Cd 0.0001 μg l–1、La 0.00008 μg l–1、 W 为 0.0001 μg l–1，U 为 0.0002 μg l–1。在整个实验过程中，V、Mo、Cd、La、W 和 U 的重复测量 (n = 3) 相对标准偏差在开放海水样品中的浓度水平分别为 5.4、6.6、7.8、5.6、3.1 和 1.6%。 17个采样点采集的表层海水样品中溶解的Mo、U、V和W浓度如图1所示。从数据可以估算出Mo、U和V的平均浓度分别为10.2±1.7μg·l–1、3.38±0.49μg·l–1和1.60±0.17μg·l–1。所获得的浓度水平与海水中 Mo、U 和 V 的浓度几乎是合理的，5,6 尽管 Mo、U 和 V 的平均浓度的标准偏差稍大，因为它们在螯合树脂预富集中的回收率较差。 2,3 然而，应该指出的是，在 0.01 μg l–1 水平下，W 的浓度比 Mo、U 和 V 的浓度低 2 或 3 个数量级，但在 Stns 中却明显较高。比所有其他采样点的值高 1 – 3。因此，在下面的实验中进一步检查了浓度水平在0.01 μg l–1 或以下的元素。三维显示了从大阪到那霸的冲绳渡轮航线沿线 17 个采样点溶解在表层海水中的 W、Cd 和 La 的浓度变化。 675 ANALYTICAL SCIENCES JULY 2000，VOL. 16 2000 © 日本分析化学会
extremely low, but often reflect some changes of the aquatic environment due to the biological activities or the environmental pollution from some artificial sources. Thus, the monitoring of trace metals in coastal and open seawater is very much required for environmental conservation. Seawater sampling in coastal and open sea areas, however, is generally a difficult and tedious work. Thus, in the present experiment, an automatic sampling system for the on-board collection of surface seawater was installed on a ferryboat (Kuroshio-maru; Kansai Kisen, Osaka), and surface seawater samples were collected at 17 sampling points along the ferry track between Osaka and Naha during December 5 – 7, 1996.1 The concentrations of trace metals in surface seawater were determined by ICP-MS (inductively coupled plasma mass spectrometry) after the chelating resin preconcentration.2 The seawater samples were collected at 5 m below the surface water through a stainless pipe line which was set up on the bottom of the ship. Although a part of the seawater sample at each sampling point was non-filtered, the remainder of the seawater sample was filtered by a membrane filter (pore size 0.45 μm) immediately after sampling. Both of these non-filtered and filtered samples were acidified to pH 1 with nitric acid. In the present experiment, however, only the sample with filtration was subjected to a determination of the total concentrations of dissolved trace metals in seawater. Bottles of the high-density polyethylene were used for sample preservation. Trace metals in seawater samples were preconcentrated by the following procedure prior to the determination by ICP-MS.2,3 First, 250 ml of the seawater sample was taken in a beaker, and the pH of the sample was adjusted at pH 6, using an acetic acid solution and an aqueous ammonia solution. Then, 0.2 g (dry weight) of chelating resin (Chelex-100) purchased from BioRad Laboratories (Richmond, CA, USA) was added to the seawater sample, and the sample solution was stirred for 2 h with a magnetic stirrer. The seawater sample was filtered with a glass filter (G4), and the chelating resin on the filter was rinsed with 8 ml of a 1 M ammonium acetate solution to elute any Mg and Ca partly adsorbed on the chelating resin. Finally, any analyte metals adsorbed on the chelating resin were eluted with 6 ml of 2 M HNO3 solution, into which 0.5 ml of a mixed solution of Ge, In, Re, and Tl (100 μg l–1 each) was added as internal standard elements. As a result, about a 40-fold preconcentration in volume was achieved. This solution was provided as an analysis solution to the ICP-MS measurements. About 25 trace metals can be determined by the present method,2 although the following discussion is limited to only oxoanion-forming elements (V, Mo, W, and U), Cd and La. The analytical detection limits of the analyte elements examined in the present experiment were estimated as follows.4 First, the instrument detection limits were obtained as the concentrations of analyte elements corresponding to 3-times the relative standard deviation (3σ) of the blank signal intensities at each m/z in the ICP-MS measurement, when 2 M HNO3 was used as the blank solution. Then, the analytical detection limits were calculated from the instrumental detection limits, while taking into account the preconcentration factors and the recovery values in the chelating resin preconcentration.2 The thus-obtained analytical detection limits by the present analytical method were 0.001 μg l–1 for V, 0.002 μg l–1 for Mo, 0.0001 μg l–1 for Cd, 0.00008 μg l–1 for La, 0.0001 μg l–1 for W, and 0.0002 μg l–1 for U. The relative standard deviations of replicate measurements (n = 3) for V, Mo, Cd, La, W, and U in the entire experimental procedure were 5.4, 6.6, 7.8, 5.6, 3.1, and 1.6%, respectively, at their concentration levels in the open seawater sample. The concentrations of dissolved Mo, U, V, and W in surface seawater samples collected at the 17 sampling points are shown in Fig. 1. It can be estimated from the data that the mean concentrations of Mo, U, and V were 10.2 ± 1.7 μg l–1, 3.38 ± 0.49 μg l–1 and 1.60 ± 0.17 μg l–1, respectively. The obtained concentration levels are almost reasonable as the concentrations of Mo, U, and V in seawater,5,6 although the standard deviations of the mean concentrations of Mo, U, and V are slightly large because of their poor recoveries in chelating resin preconcetration.2,3 However, it should be noted that the concentrations of W at the 0.01 μg l–1 level, which were lower by 2 or 3 orders of magnitude than those of Mo, U, and V, were significantly higher at Stns. 1 – 3 than those at all other sampling points. Therefore, the elements whose concentration levels were at 0.01 μg l–1 or below were further examined in a following experiment. The concentration variations of W, Cd and La dissolved in the surface seawater at the 17 sampling points along the Okinawa ferry track from Osaka to Naha are three-dimensionally shown 675 ANALYTICAL SCIENCES JULY 2000, VOL. 16 2000 © The Japan Society for Analytical Chemistry