GO-TSC composite integrated with EDXRF for ultrasensitive determination of trace Hg(II) in water via solid-phase preconcentration.

Conventional laboratory methods such as ICP-MS and AAS require complex pretreatment, lengthy analysis, and expensive instrumentation, making them inadequate for rapid on-site mercury monitoring. Although Energy-Dispersive X-ray Fluorescence (EDXRF) is a promising field-deployable technique, its direct application to liquid samples faces three critical challenges: (1) strong absorption and scattering of X-rays by the aqueous matrix severely reduce excitation efficiency, limiting detection limits to only the mg L-1 level-far above the 1 μg L-1 regulatory requirement; (2) complex and variable water matrices cause pronounced matrix effects that compromise quantitative accuracy; (3) mercury's volatility and chemical instability in liquid samples complicate preservation and introduce bias. To overcome these limitations, this study proposes a GO-TSC/thin-layer EDXRF enrichment strategy. Carboxyl dimine-grafted S/N ligand-modified graphene oxide (GO-TSC) adsorbent selectively captures Hg2+ via HSAB soft-soft coordination. Enrichment followed by vacuum filtration forms a uniform thin film, eliminating water attenuation. Optimized conditions (pH 3, 70 °C, 40 min; Rh target 9 W, 300 s) with Compton-scattering normalization effectively correct for deposition nonuniformity. The method exhibits a linear range of 10-8000 μg L-1 (R2 > 0.9928) and an LOD of 0.26 μg L-1 (≈3 orders of magnitude lower than direct measurement). RSD < 3.2%, strong anti-interference (coexisting ions at 4 ppm yield < 5% signal change), and 7-day signal loss < 4.5%. Notably, the LOQ of 0.87 μg L-1 is below the WHO permissible limit of 1.0 μg L-1, confirming that the method can accurately quantify Hg(II) at the regulatory borderline. Wastewater spike recoveries are 96.55-102.84%, in agreement with ICP-MS. This platform integrates selective enrichment, matrix simplification, and portable detection, offering a practical solution for on-site trace Hg monitoring.