Heating-assisted chelating resin enrichment for laser-induced breakdown spectroscopy of heavy metals in water

Laser-induced breakdown spectroscopy (LIBS) shows promise for trace heavy metal analysis in water, but direct detection suffers from poor sensitivity due to plasma quenching and splashing. Chelating resin enrichment can improve sensitivity, yet conventional room-temperature solid-phase extraction (SPE) is limited by slow mass transfer and incomplete recovery, especially when metal ions are bound by natural organic complexes. Here, we introduce controlled heating (50 °C) as a kinetic regulation strategy during D403 resin enrichment. Compared to room-temperature SPE (20 °C), mild heating reduces solution viscosity by ∼40%, enhances diffusion (Stokes-Einstein), and dissociates weak metal-organic complexes (activation energies 15-40 kJ mol^-1) without degrading the resin. Under optimized conditions (pH 3.0; 35 min), detection limits for Cu and Ni improve by 61% and 52%, reaching 0.0302 and 0.1097 mg L^-1, respectively. Calibration linearity (R² > 0.96) and precision (RSD drops from 12.8% to 8.4% for Cu) are also enhanced. Spike recoveries in real tap water at two concentration levels (0.5 and 2.0 mg L^-1; n = 3) are 115.5% and 111.1% for Cu, and 113.8% and 97.5% for Ni, respectively, all within the 80-120% acceptance range. These results demonstrate that controlled heating effectively overcomes kinetic bottlenecks of room-temperature SPE, providing a simple, robust, and cost-effective method for routine monitoring of trace heavy metals in environmental waters.