U.S. flag

An official website of the United States government, Department of Justice.

LIBS for Soil Screening Study of Matrix Effects on Elemental Profiling

NCJ Number
Date Published
March 2018
39 pages
The findings and methodology are presented for a project that quantified the matrix effects (moisture and texture) on the LIBS (Laser Induced Breakdown Spectroscopy) elemental analysis of soil samples and correct for them for a reproducible elemental profile.

The overall conclusion of this study is that when LIBS is used in the field for soil analysis, a general protocol is not recommended; and for quantitative decisionmaking, even screening, the dehydration of samples in a particulate form and their compaction into a pellet with high density are necessary. The study consisted of three steps. First, the effect of moisture content on the LIBS signal and its reproducibility were studied for three types of grain size (sand-type, silt-type, and clay-type). The study first investigated the elemental profile of major elements and then minor elements. Validation with certified NIST samples was performed. Second, once the effect of moisture and temperature were understood on "pure soils," the project progressed to more realistic soils. Controlled mixtures of sand-type, silt-type, and clay-type powders were fabricated to simulate soil textures and extended the conclusions of the first step. Validation with certified soil NIST samples was performed. Third, based on the conclusions from the previous two steps, a spectral correction protocol was established to be able to correct the LIBS emission spectra and retrieve the correct elemental signature by compensating for the eventual unknown physical state of the soil (moisture, type, and grain size). This correction was spectrum-based and included physical information from the plasma rather than uncontrolled multivariate analysis. 25 figures and 18 references

Date Published: March 1, 2018