This work describes a novel conductometric/spectrophotometric method to determine the ionic strength (I) of dilute aqueous solutions (e.g., natural waters from rivers and lakes). Because I ≤ 0.01 mol kg⁻¹ in such waters, precision as well as accuracy is of paramount importance. In current practice the ionic strength of natural waters is determined almost exclusively with conductometric measurements. We used solutions of artificial freshwater to assess the performance of two commonly used types of conductometric instruments and found that a conductivity probe systematically overestimated I while a salinometer systematically underestimated I. We therefore recommend here an empirical correction that can be easily implemented to improve the accuracy of both types of conductivity measurements. Additional improvement in measurements of I can be achieved by using that high-quality conductometric measurement as input to a hybrid conductometric/spectrophotometric procedure that makes use of robust quantitative characterizations of the influence of ionic strength on the dissociation characteristics of phosphate pH buffers and sulfonephthalein pH indicators. This approach mitigates systematic conductometric errors associated with solution composition, thus yielding measurements of ionic strength with substantially improved accuracy and precision. The method was validated by testing on a broad suite of artificial freshwaters (n = 64) with compositions that include the major ions present in dilute natural waters (Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl⁻, HCO₃⁻, and SO₄²⁻). This new hybrid method is applicable to waters of 0 ≤ I ≤ 0.01 mol kg⁻¹ (i.e., electrical conductivity of up to 900 μS cm⁻¹ at 25 °C), with an accuracy of ±0.0003 and a precision of ±0.0003.

这项工作描述了一种新的电导/分光光度法来确定稀水溶液（例如，来自河流和湖泊的天然水）的离子强度 ( I )。因为在这样的水域中I  ≤ 0.01 mol kg ^-1，所以精度和准确度至关重要。在目前的实践中，天然水的离子强度几乎完全通过电导测量来确定。我们使用人造淡水溶液来评估两种常用类型的电导仪的性能，发现电导率探针系统地高估了I而盐度计系统地低估了I. 因此，我们在此推荐一种可以轻松实施的经验校正，以提高两种电导率测量的准确性。通过使用高质量电导测量作为混合电导/分光光度程序的输入，可以实现I测量的额外改进，该程序利用离子强度对磷酸盐 pH 缓冲液和磺酞 pH 解离特性影响的稳健定量表征指标。这种方法减轻了与溶液成分相关的系统电导误差，从而产生具有显着提高的准确度和精度的离子强度测量。该方法通过对广泛的人工淡水（n = 64)，其成分包括存在于稀释的天然水中的主要离子（Na ⁺、K ⁺、Mg ²⁺、Ca ²⁺、Cl ^-、HCO ₃ ^-和 SO ₄ ^2-）。这种新的混合方法适用于 0 ≤  I  ≤ 0.01 mol kg ^-1的水（即，在 25 °C 时电导率高达 900 μS cm ^-1  ），精度为 ±0.0003，精度为 ±0.0003。