Chitosan-regulated TXRF for trace rubidium and cesium detection in high-salinity brine

To address the critical challenge of trace Rb/Cs detection in high-salinity brine (TDS >300 g L^-1)-where matrix effects from dominant ions (Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl^-) severely limit conventional techniques-this study pioneers chitosan (CS)-regulated total reflection X-ray fluorescence (TXRF) methodology. The primary objective was to overcome two key bottlenecks in high-salinity TXRF analysis: (1) coffee-ring effect (CRE) induced by uncontrolled salt crystallization, and (2) signal instability caused by salt-film deliquescence. By leveraging the dual functionality of chitosan-where amino/hydroxyl groups regulate salt crystallization dynamics to suppress CRE, while intrinsic film-forming properties mitigate deliquescence- synergistically integrated morphological control with internal standard correction (using Sm/Se). This approach achieved uniform analyte distribution and compensated for matrix absorption, enabling direct analysis of minimally diluted brine samples. Under optimized conditions (0.4 % CS, 8 μL sample volume, 50 °C drying), the method demonstrated high sensitivity (LOD: 0.027 mg L^-1 for Rb, 0.051 mg L^-1 for Cs) and accuracy (R² > 0.99). Validation using real brine samples from Chaka, Qarhan, and Qaidam Basin salt lakes showed concordance with ICP-OES (relative errors <11.5 %), meeting industrial standards. This work establishes a rapid, low-pretreatment strategy for Rb/Cs quantification in hypersaline environments, thus providing a new strategy for detecting Rb and Cs in high-salinity brine resources.