This article describes the development and validation of an analytical procedure for the matrix separation, preconcentration and determination of sub-ng kg-1 levels 232Th in a small volume (20 mL) of seawater samples. The matrix separation and Th preconcentration was carried out using a commercially available ion-chelation system seaFAST-pico. The acidified to pH < 2 seawater samples were mixed on-line with the ammonium acetate buffer (pH of 6.0 ± 0.2) before loading on the column containing resin with iminodiacetic and ethylenediaminetriacetic functional groups. At this pH, 232Th was quantitatively retained on the resin, demonstrating a good affinity (selectivity) for Th in seawater matrix. The element retained on the resin was eluted using only 0.2 mL of 1.8 M HNO3 enabling to achieve high preconcentration factor. The pretreatment procedure, with two sample loading cycles (each one 10 mL), was accomplished in about 25 min. Determining 232Th mass fraction in seawater samples was based on isotope dilution inductively coupled plasma mass spectrometry (ID ICP-MS) method, which was considered as the most accurate calibration strategy for precise quantification of 232Th mass fraction in seawater samples. ISO/IEC17025 and Eurachem guidelines were followed to perform the validation of the developed in this study procedure. In the case of seawater samples with natural level of thorium the major contributions to the expanded uncertainty arose from the uncertainty associated with isotopic ratio measurements in the isotopically spiked sample, followed by the correction for procedural blank and the correction for mass discrimination effect. The estimated method detection limit for 232Th was 0.005 ng kg-1. The developed method was successfully applied to the determination of 232Th mass fraction in seawater reference samples: IAEA-443, SLEW-3, NASS-4, NASS-6, and CASS-5. Although 232Th is not certified in any of the seawater reference materials, a good agreement was obtained between the results in this study and data published elsewhere.

中文翻译：

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基质分离预浓缩后ICP-SFMS测定海水中超痕量232 Th

本文介绍了用于基质分离、预浓缩和测定小体积 (20 mL) 海水样品中亚 ng kg-1 水平 232Th 的分析程序的开发和验证。使用市售的离子螯合系统 seaFAST-pico 进行基质分离和 Th 预浓缩。酸化至 pH < 2 的海水样品与醋酸铵缓冲液（pH 值为 6.0 ± 0.2）在线混合，然后加载到含有带有亚氨基二乙酸和乙二胺三乙酸官能团的树脂的柱子上。在此 pH 值下，232Th 定量保留在树脂上，表明对海水基质中的 Th 具有良好的亲和力（选择性）。仅使用 0.2 mL 1.8 M HNO3 即可洗脱树脂上保留的元素，从而实现高预浓缩因子。预处理程序，两个样品加载循环（每个 10 mL），在大约 25 分钟内完成。测定海水样品中的 232Th 质量分数基于同位素稀释电感耦合等离子体质谱 (ID ICP-MS) 方法，该方法被认为是精确定量海水样品中 232Th 质量分数的最准确的校准策略。遵循 ISO/IEC17025 和 Eurachem 指南对本研究程序中的开发进行验证。在具有天然钍含量的海水样品的情况下，扩大不确定性的主要贡献来自与同位素加标样品中同位素比测量相关的不确定性，其次是对程序空白的校正和对质量歧视效应的校正。232Th 的估计方法检测限为 0。005 ng kg-1。所开发的方法已成功应用于测定海水参考样品中的 232Th 质量分数：IAEA-443、SLEW-3、NASS-4、NASS-6 和 CASS-5。尽管 232Th 未在任何海水参考材料中得到认证，但本研究的结果与其他地方发表的数据之间取得了良好的一致性。