Lateral resolution of DGT LA-ICP-MS for chemical imaging of metal solutes

Diffusive gradients in thin films (DGT) coupled with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is increasingly applied for high-resolution chemical imaging of metal solutes, yet its effective lateral resolution has not been quantitatively assessed. This study provides the first targeted investigation of the lateral resolution achievable with state-of-the-art DGT LA-ICP-MS using copper (Cu) as a model analyte in three complementary experimental designs that isolate diffusion-controlled, geometry-controlled, and material-controlled constraints: (i) Controlled solute transport through a polytetrafluoroethylene (PTFE) foil with 5-100 µm holes revealed differential time-dependent broadening of solute and matrix patterns and the transition from geometry-preserving to diffusion-dominated behaviour. Full width at half maximum/minimum (FWHM)-based analysis showed very small apparent lateral "imaging-blur" coefficients for DGT-bound metals (Cu/Zn ≈10^-15-10^-13 m² s^-1), i.e., several orders of magnitude lower than typical ionic diffusion in hydrogels (≈10^-10 m² s^-1), consistent with rapid immobilization at the DGT binding phases and modest lateral within-gel diffusion. (ii) Direct gel contact with Cu metal grids enabled quantitative comparison of nominal bar/hole dimensions with DGT-derived solute patterns, demonstrating that features down to ~25 µm are detectable under optimal contact and laser ablation conditions. (iii) Application to printed circuit boards confirmed the method's ability to reproduce sub-mm Cu features on technologically relevant materials. Across experiments, gel-phase lateral diffusion and imperfect gel-sample contact were the dominant factors limiting spatial accuracy. These results define the practical lateral resolution of DGT LA-ICP-MS and provide guidance for designing and interpreting high-resolution solute imaging experiments in environmental and materials science.