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Determination of the isotopic composition of enriched materials using laser ablation molecular isotopic spectrometry: partial least squares and multivariate curve resolution for the determination of 15N content in enriched urea
摘要： A quantitative analytical method based on laser ablation molecular isotopic spectrometry (LAMIS) and multivariate analysis was developed and evaluated for the determination of the isotopic composition of enriched materials. The method consists preparing a concentrated solution of the enriched material, using small quantities of a sample (125 mg), and ensuring the economic efficiency of the analysis. Standard solutions of known isotopic contents are prepared by employing mixtures of urea highly enriched in 15N and urea of natural isotopic ratio and analyzed by mass spectrometry. A small volume (30 μL) of these solutions is delivered to a filter paper disc (3 cm diameter). After drying, the disc, offering a homogeneously distributed analyte, is presented to a LAMIS equipment to acquire the vibronic emission spectra containing information about the isotopologues of interest. To illustrate the proposed method, the content of 15N is determined in enriched samples of urea. In this case, each spectrum is normalized by the intensity of emission of the CN isotopologues for the electronic (Δν = 0) emission band at 387.1 nm, ensuring better accuracy. Selected regions and single wavelengths of the vibronic emission spectrum (Δν = + 1 or ? 1) related to CN species were employed to construct multivariate partial least squares (PLS) and univariate regression models to predict the isotopic content of new samples. Besides, the LAMIS data set was evaluated by multivariate curve resolution (MCR) algorithm. The best MCR and PLS models presented similar results regarding the accuracy to determine 15N content in enriched urea. MCR is capable of identifying spectral interferences and minimizing its effect. The results show that the proposed method based on LAMIS and PLS or MCR multivariate analysis can determine the 15N content in the range 5–50% with a root mean square error of prediction (RMSEP) respectively equal to 0.5 or 0.7% (m/m) in comparison with reference results obtained by mass spectrometry.
关键词： 15N determination in enriched urea,Laser ablation molecular isotopic spectrometry (LAMIS),Isotopic composition of enriched materials,Partial least squares,Multivariate regression,Multivariate curve resolution (MCR)
更新于2025-09-23 15:19:57
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Hydrogen isotopic analysis using molecular emission from laser-induced plasma on liquid and frozen water
摘要： The hydrogen isotopes in liquid and frozen water samples were analyzed by laser ablation molecular isotopic spectrometry (LAMIS), which employs the molecular emission from laser-induced plasma for isotope analysis. Molecular emission bands of OH and NH radicals were observed, and their spectral features were characterized in accordance with sample matrix and measurement conditions. The OH and NH bands exhibit different emission behavior, which was attributed to formation kinetics and thermodynamic factors. Under optimized condition, isotopic shift between hydrogenated (OH and NH) and deuterated (OD and ND) species was measured at individual rotational branches. By using these molecular bands, the partial least squares regression (PLSR) structure was established for quantitative analysis of hydrogen isotope and evaluated by cross-validation in terms of accuracy and precision. The PLSR result was good with root mean square error of prediction (RMSEP) of 0.3–0.7% for all species. Particularly, the case using OH/OD emission from liquid water revealed the most accurate result with RMSEP of 0.33%. It was affected by the quality and reproducibility of spectral data determined by utilized species. This study not only supports the behavioral understanding of molecular radicals in laser-induced plasma, but also identifies the feasibility of LAMIS for real-time application to quantitative analysis in various sample matrices.
关键词： Hydrogen isotope,LAMIS,Matrix effect,PLSR,Molecular emission band
更新于2025-09-12 10:27:22