Palladium, which is used in various fields, including automobile catalysis, is a precious metal with an extremely low content (0.4 μg/kg) in the earth's crust. Previous studies have suggested its release from anthropogenic sources into a wide range of environments, including aquatic environments. However, reliable analytical methods by which it can be quantified have not yet been established owing to its extremely low concentration in aquatic environments and the vulnerability of its measurements to interfering elements. Therefore, the aim of this study was to establish a highly sensitive and accurate analytical method for its quantification in open ocean seawater using isotope dilution-inductively coupled plasma mass spectrometry (ICP-MS) and thereafter, clarify its vertical distribution. To establish the analytical method, the effects of the concentrations and compositions of the cleaning solution and eluent used during the column pre-concentration process on the analysis were examined. Further, we applied the ammonia dynamic reaction cell (NH₃ DRC) during ICP-MS measurements and also optimized the NH₃ gas flow rate as well as rejection parameter, q (Rpq). The open ocean seawater samples were acidified to obtain 0.5 M HCl concentration followed by the addition of ¹⁰⁵Pd isotope enriched spike solution. Thereafter, the samples were allowed to stand for 24 h before analysis. Solid-phase extraction of Pd in seawater was performed using an anion exchange resin (AG1-X8). To remove interfering elements, a cleaning method was employed. Specifically, cadmium, with the most significant effect on Pd measurements, was removed using HNO₃ (> 0.5 M), while other interfering species, including strontium and zirconium were removed using either HCl or HNO₃. The flow rate of the cleaning solution and the eluate were also optimized. Thus, a pre-concentration method with a Pd recovery rate of 89–95% was established. Furthermore, the isobaric interference caused by ⁹⁰Zr¹⁶O⁺, which increased the procedural blank value of our analytical method and could not be completely removed during pre-concentration, was eliminated by employing NH₃ DRC in the ICP-MS process, while that caused by ⁸⁸Sr¹⁴N¹H₃⁺ was suppressed by setting the NH₃ gas flow rate above 1.8 mL/min and the Rpq at 0.81. Thus, when 470 mL of open ocean seawater samples were analyzed under these conditions, the detection limit and blank value obtained were 0.060 and 0.050 pmol/L, respectively (both of which are lower than previously reported values). Additionally, an investigation of the vertical distribution of Pd in the North Pacific using the established methods revealed that Pd concentrations showed a tendency to decreased from 0.32 pmol/L at depth of 50 m to 0.10 pmol/L at a depth of 1500 m, and at depths below 2000 m, the concentrations varied in the range 0.10–0.13 pmol/L. Therefore, our established method showed sufficient suitability for the determination of the sub-picomolar concentration of Pd in open ocean seawater.

钯用于汽车催化等各个领域，是地壳中含量极低（0.4微克/千克）的贵金属。以前的研究表明它从人为来源释放到广泛的环境中，包括水生环境. 然而，由于其在水生环境中的浓度极低以及其测量值对干扰元素的脆弱性，尚未建立可以对其进行量化的可靠分析方法。因此，本研究的目的是建立一种高灵敏度和准确的分析方法，用于使用同位素稀释电感耦合等离子体质谱 (ICP-MS) 在公海海水中对其进行定量，然后明确其垂直分布。为了建立分析方法，检查了色谱柱预浓缩过程中使用的清洗液和洗脱液的浓度和组成对分析的影响。此外，我们应用氨动态反应池（NH₃DRC) 在 ICP-MS 测量期间，还优化了 NH ₃气体流速以及排斥参数 q (Rpq)。将公海海水样品酸化以获得 0.5 M HCl 浓度，然后添加¹⁰⁵ Pd 同位素富集的加标溶液。此后，样品在分析前静置 24 小时。使用阴离子交换树脂 (AG1-X8) 对海水中的 Pd 进行固相萃取。为了去除干扰元素，采用了清洁方法。具体来说，对 Pd 测量影响最显着的镉是使用 HNO ₃ (> 0.5 M) 去除的，而其他干扰物质，包括锶和锆，则使用 HCl 或 HNO _3去除. 清洗液和洗脱液的流速也进行了优化。因此，建立了 Pd 回收率为 89-95% 的预浓缩方法。此外，在 ICP-MS 过程中采用 NH _{3 DRC 消除了由}⁹⁰ Zr ¹⁶ O ⁺引起的同量异位素干扰，该干扰增加了我们分析方法的程序空白值，并且在预浓缩过程中无法完全去除，而由⁸⁸ Sr ¹⁴ N ¹ H ₃ ^{+引起的通过设置 NH} ₃被抑制气体流速高于 1.8 mL/min，Rpq 为 0.81。因此，当在这些条件下分析 470 mL 的公海海水样品时，获得的检测限和空白值分别为 0.060 和 0.050 pmol/L（均低于先前报道的值）。此外，使用已建立的方法对北太平洋 Pd 垂直分布的调查表明，Pd 浓度呈现出从 50 m 深度的 0.32 pmol/L 下降到 1500 m 深度的 0.10 pmol/L 的趋势，并且在 2000 m 以下的深度，浓度变化范围为 0.10-0.13 pmol/L。因此，我们建立的方法显示出足够适用于测定公海海水中亚皮摩尔浓度的 Pd。