Muñiz López, Wilmaris

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    High explosives detection in international mail using See-Through Raman Spectroscopy assisted by multivariate analysis
    (2020-12-09) Muñiz López, Wilmaris; Hernández Rivera, Samuel P.; College of Arts and Sciences - Sciences; Torres Candelaria, Jessica; Román Velázquez, Félix R.; Department of Chemistry; Rodríguez, Domingo
    See-Through Raman Spectroscopy (STRS) was used for the non-invasive, non-destructive sample analysis of high explosives (HEs) in mail envelopes or flats. The method resulted in a safe and rapid analysis of HEs: ammonium nitrate (AN), urea nitrate (UN), and pentaerythritol tetranitrate (PETN). The analysis was carried on under normal conditions without sample preparation to simulate a scenario similar to the ones found at an International Mail Facility (IMF). The ST-RS system operates under high photon scattering conditions enables a deeper penetration by the incident laser beam. It is a portable, rapid, high throughput technology that enables the characterization of chemical and biological threats (CBTs) by exciting their vibrational modes. Multivariate analysis (MVA) was applied due to the vast amount of data generated in the experiments, and the spectral interferences presented by the envelopes (flats). Under these conditions, it was complicated to obtain robust results in a short time. Exploratory Data Analysis (EDA) was applied to separate HEs signals from mail flats spectral data. Principal Component Analysis (PCA) was capable of classifying each variable, explaining most of the experimental variance using the first two principal components: PC-1 and PC-2. The PCA-based models were efficient in classifying HEs' vibrational markers even when contained within several flats layers and classifying HEs into different clusters. PC loadings were used to determine each variable's contribution to the PCA models, which resulted in correlation coefficients (R^2 values) of 0.99 and 0.92 for the first PC for UN and PETN, respectively.