Study of Matrix Effects in Laser-Induced Breakdown Spectroscopy by Different Sample Preparation

Laser-induced breakdown spectroscopy (LIBS) has become a promising technology for real-time characterization of soil properties. However, due to the inherent microscale heterogeneity of granular materials like soil, spectral emission lines can be highly variable. To investigate the effects of moisture and heterogeneity, we performed qualitative and quantitative analysis on several field moist, air-dried, and ground, air-dried soil samples with differing elemental concentrations. Principal component analysis was carried out to extract features from raw spectra. Matrix effects on Al, Ca, Fe, Mg, Na and K, were investigated. We found that even if the elemental concentration is different, samples prepared in the same way, have spectra with similar features. We were able to discriminate spectra from moist and dried, ground samples with 100% accuracy using a support vector machine, while the unground dry samples, which did not have outstanding features, were differentiated with 50% accuracy. When samples are ground, elemental prediction was improved for all elements except for Fe, indicating that microscale heterogeneity can be reduced by grinding samples. Unlike the other elements, Fe estimation was better on moist samples, which may be due to the interaction of iron minerals with soil moisture.