High-resolution single pulse LA-ICP-MS mapping via 2D sub-pixel oversampling on orthogonal and hexagonal ablation...

Area of Science:

• Analytical Chemistry
• Geochemistry
• Materials Science

Background:

• Laser beam profiles in LA-ICP-MS are often super-Gaussian, not flat-top, affecting ablation volume.
• The sampled material and spatial resolution depend on laser beam profile and ablation grid.
• Small laser beam sizes (<5 μm) approach Gaussian profiles, further influencing sampling accuracy.

Purpose of the Study:

• To investigate the impact of different ablation grid sampling strategies on LA-ICP-MS mapping quality.
• To evaluate the benefits of hexagonal sampling over orthogonal sampling for improved spatial resolution and signal-to-noise ratio.
• To develop computational tools for simulating LA-ICP-MS mapping and studying sampling effects.

Main Methods:

• Simulated LA-ICP-MS mapping using discrete convolution with crater profiles as kernels.
• Incorporated Poisson and Flicker noise to mimic real-world instrumental and concentration variations.
• Developed a freely accessible online application for virtual ablation experiments with phantoms.
• Investigated orthogonal and hexagonal sampling grids with varying degrees of contraction (sub-pixel mapping).

Main Results:

• Contraction of the ablation grid (sub-pixel mapping) enhances surface sampling accuracy, pixel density, and signal-to-noise ratio.
• Hexagonal sampling demonstrates potential for improved image quality due to more compact packing and reduced anisotropy compared to orthogonal grids.
• Simulations revealed that hexagonal grids offer advantages in spatial resolution and signal-to-noise ratio, particularly for smaller features.
• Experimental validation was limited to larger beam sizes (150 μm) due to hardware constraints.

Conclusions:

• Computational simulation is a valuable tool for studying LA-ICP-MS sampling strategies, especially when experimental limitations exist.
• Hexagonal sampling offers significant advantages for high-resolution LA-ICP-MS imaging, warranting further development of precise sampling stages.
• Optimizing ablation grid design and sampling strategies is crucial for maximizing the analytical performance of LA-ICP-MS.