Analyses of marine carbonates using solution-based ICP-MS typically occur in dilute acid, as alkaline solutions can cause CaCO₃ and metal-oxide/oxyhydroxide precipitation. Measurement of iodine to calcium (I/Ca) ratios in marine carbonates—most often in the calcite shells, or tests, of foraminifera—are challenging to pair with those of pH-sensitive metals, as iodine is unstable in acidic solution and will volatilize in the presence of light and air. As a result, I/Ca ratios are routinely analyzed in basic solution, requiring additional sample material and analytical time. Leveraging the equilibrium relationships between thermodynamically stable, inorganic iodine species across a wide range of electrochemical potential (pE) and pH values, we determine which species are present in low-temperature, aqueous solutions characteristic of marine carbonate analysis on quadrupole ICP-MS, and suggest appropriate solution pH(s) for iodine measurement. Our results demonstrate that iodine is capable of volatilization at all pH values <10.5, though it is most volatile in the pH range of 0–1. Furthermore, at pH values above 10.5, solutions are susceptible to contamination from gas-phase molecular iodine, I₂.

Employing this knowledge of iodine speciation, we establish a high precision method for the solution-based analysis of iodine alongside twelve other elements (Li, Na, Mg, Al, Mn, Fe, Zn, Sr, Cd, Ba, U, and Ca) on a collision-reaction cell equipped quadrupole ICP-MS in the acidic pH range. Using a 9:1 volume/volume mixture of 0.5% tetramethylammonium hydroxide (TMAH) and 2% nitric acid (HNO₃), we can reproducibly analyze iodine concentrations in a complex carbonate (calcite and aragonite) matrix alongside other elemental ratios used in paleo-environmental reconstructions. This mixture of dilute acid and base maintains acidic pH (1.5 ± 0.14), avoiding the precipitation of pH-sensitive metal oxides/oxyhydroxides and CaCO₃ while minimizing iodine volatilization. We demonstrate that iodine concentrations measured using ICP-MS are only effectively stabilized in the pH range of 1.5–10.5 and recommend pH-matching sample and standard solutions. This method allows the extraction of considerably more directly comparable paleo-environmental information from the analysis of a single foraminiferal sample.

使用基于溶液的 ICP-MS 分析海洋碳酸盐通常在稀酸中进行，因为碱性溶液会导致 CaCO ₃和金属氧化物/羟基氧化物沉淀。测量海洋碳酸盐中的碘与钙 (I/Ca) 比（通常在有孔虫的方解石壳或测试中）与那些对 pH 值敏感的金属配对具有挑战性，因为碘在酸性溶液中不稳定并会挥发在有光和空气的情况下。因此，I/Ca 比率通常在碱性溶液中进行分析，需要额外的样品材料和分析时间。利用热力学稳定的无机碘物质在广泛的电化学电位 (pE) 和 pH 值范围内的平衡关系，我们确定了哪些物质存在于低温水溶液中，在四极杆 ICP-MS 上进行海洋碳酸盐分析的特征，以及建议适当的溶液 pH 值用于碘测量。我们的结果表明，碘能够在所有 pH 值 <10.5 的情况下挥发，尽管它在 0-1 的 pH 范围内最易挥发。此外，在 pH 值高于 10.5 时，溶液容易受到气相分子碘的污染，I₂ .

利用碘形态的这一知识，我们建立了一种基于溶液分析碘以及其他十二种元素（Li、Na、Mg、Al、Mn、Fe、Zn、Sr、Cd、Ba、U 和 Ca）的高精度方法) 在酸性 pH 范围内配备有四极杆 ICP-MS 的碰撞反应池上。使用 0.5% 四甲基氢氧化铵 (TMAH) 和 2% 硝酸 (HNO ₃ ) 的 9:1 体积/体积混合物，我们可以重复分析复杂碳酸盐（方解石和文石）基质中的碘浓度以及古中使用的其他元素比例-环境重建。这种稀酸和碱的混合物保持酸性 pH (1.5 ± 0.14)，避免对 pH 敏感的金属氧化物/羟基氧化物和 CaCO _3的沉淀同时最大限度地减少碘的挥发。我们证明使用 ICP-MS 测量的碘浓度仅在 1.5–10.5 的 pH 范围内有效稳定，并推荐使用 pH 匹配的样品和标准溶液。该方法允许从单个有孔虫样本的分析中提取更直接可比较的古环境信息。