研究目的
The aim of the study was the evaluation of di?erent quanti?cation approaches for LIBS data which consider the matrix e?ect. Another goal was to explore how a calibration obtained for one ?eld can be transferred to another one.
研究成果
The second univariate method yielded better calibration and prediction results compared to the first method, since matrix effects were better accounted for. PLSR did not strongly improve the prediction in comparison to the second univariate method.
研究不足
The matrix dependence of the LIBS signal necessitates careful data evaluation. The accuracy of standard-free LIBS approaches for the analysis of the very complex matrix soil is still unsatisfactory.
1:Experimental Design and Method Selection
Different calibration approaches for soil LIBS data were presented, including univariate calibration by standard addition, univariate model derived from reference analytics, and multivariate calibration approach based on partial least squares regression (PLSR).
2:Sample Selection and Data Sources
139 soil samples collected on two neighboring agricultural fields in a quaternary landscape of northeast Germany with very variable soils. Reference analysis was carried out by inductively coupled plasma optical emission spectroscopy after wet digestion.
3:List of Experimental Equipment and Materials
Nd:YAG laser (Quanta-Ray, Spectra-Physics), echelle spectrometer (Aryelle Butterfly, LTB), ICCD camera (iStar, AndorTechnology), Veris 3100 system (Veris Technologies).
4:Experimental Procedures and Operational Workflow
The plasma was created using UV radiation (355 nm). Emissions were collected by a concave mirror, coupled into an optical fiber and guided to an echelle spectrometer. A total of 200 single shot spectra were recorded per sample in the UV as well as in the VIS range.
5:Data Analysis Methods
Pretreatment of the LIBS spectra consisted of outlier removal. For PLSR calibration, spectra were mean centered. Logarithms of the known element mass fractions were used as y variables when the data distribution was strongly skewed.
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