Investigation of the CL-resin® properties for a sulfur-free content molecule protocol

The accurate quantification of chlorine, and particularly of ³⁶Cl, remains challenging due to severe spectral interferences and the incompatibility of conventional sulfur-based purification protocols with ICP-MS/MS analysis. In this study, we report on the development and validation of a short, sulfur-free purification protocol for chlorine using CL-resin®, specifically optimized for ultra-trace measurements by ICP-MS/MS. Water was demonstrated to be as effective as 1 M H₂SO₄ as a preconditioning and percolating solvent, while offering clear advantages in terms of safety, simplicity, and chemical compatibility. Among the percolating solvents evaluated, water and 4 mM nitromethane provided comparable chlorine retention and recovery over a wide range of flow rates and percolated volumes; however, water was selected for routine use due to the hazardous nature of nitromethane. In contrast, 6 mM sodium carbonate showed a strong dependence on percolated volume, limiting its applicability to small sample volumes. For chlorine elution, cyanate was identified as a robust and efficient sulfur-free alternative to thiocyanate, enabling near-quantitative chlorine recovery (∼90%) under mild and reproducible conditions. The removal step dedicated to ¹⁴C elimination, required for liquid scintillation counting, was successfully suppressed, resulting in a shortened protocol fully compatible with ICP-MS/MS detection. The optimized method allows the percolation of up to 2 L of sample, significantly improving detection limits. Overall, this work provides a robust, scalable, and ICP-MS/MS-compatible purification strategy for chlorine and ³⁶Cl, well suited for environmental monitoring, nuclear decommissioning, and ultra-trace analysis, where sulfur-free chemistry and high recovery yields are essential.