Soil Sensing With a Handheld <scp>LIBS</scp> : Effect of Sample Preparation and Instrument Precision

ABSTRACT Rapid and scalable methods for characterising soil elements are needed to understand soil conditions. Handheld Laser‐Induced Breakdown Spectroscopy (LIBS) enables simultaneous multi‐element analysis, but it requires sample preparation by grinding and pelleting, which is challenging for sandy soils due to their poor cohesion. Here, we investigated the effects of grinding time and binder addition on pellet integrity, LIBS spectra and measurement precision. We prepared soils with varying sand contents (10%–90%) and assessed pelleting consistency after grinding for 3, 5, 7, or 15 min. To improve cohesion, we remixed with 20% potassium bromide (KBr) as a binder. Sandier samples and shorter grinding times produced less cohesive pellets and more variable measurements. Longer grinding and KBr addition improved pellet cohesion and reduced measurement variability. However, KBr had element‐dependent effects on the relationship between spectra and element concentrations. We evaluated the precision of handheld LIBS by quantifying repeatability (shot‐to‐shot) and between‐day reproducibility. Shot‐to‐shot relative standard deviation (RSD) often exceeded 10%, but averaging multiple shots improved precision, reducing variability to less than 10% RSD. Noticeable between‐day variability was observed, influenced by both instrument and sample properties. These findings provide a foundation for guidelines on sample preparation for handheld LIBS soil analysis. Although substantial sample preparation is required, handheld LIBS offers simultaneous analysis of all elements present in the soil sample. With appropriate preparation, LIBS can improve analytical reliability and cost‐effectiveness for soil assessments, supporting applications in soil health assessments, environmental remediation and soil monitoring.