This collection is exclusively made up of theses, dissertations, and project reports submitted as a requirement for completing a graduate degree at UPR-Mayagüez.
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Browsing Theses & Dissertations by Subject "532 nm laser"
Tirado Robles, Naihomy M.; Hernández Rivera, Samuel P.; College of Arts and Sciences - Sciences; Mina, Nairmen; Rivera, Nilka; Department of Chemistry; Maldonado, Noemí
Raman spectroscopy (RS) is an excellent tool for quantitative and qualitative analysis that can be used to detect and characterize different types of substances. Transmission Raman Spectroscopy (TRS) has been used in agriculture, food chemistry, pharmaceuticals, biomedicine, and other fields. This research aimed to develop a Transmission Raman Spectrometer (TRSr) to detect opioids, concealed chemicals, and biological threats. The advantage of this technique is that the excitation source passes through the sample or its packaging instead of performing the analysis only on the sample's surface. The main components of the TRS were a diode-pumped 532 nm solid-state laser, an imaging spectrometer, a high-efficiency array detector (charge-coupled device), a laser line filter, and an edge Rayleigh filter. In addition, a commercial instrument control, data acquisition, and spectrum display software package (Andor Solis) was used for digitizing the signal, readout the spectral information, and display the Raman spectrum in the computer. A series of experiments were performed to evaluate the system performance and efficiency of the technique and instrumentation. Benzoic acid (BA) was used to test the system resolution, the transmitted intensity, and the signal-to-noise (SNR) ratio. Discrimination capabilities in binary mixtures, among other parameters in TR spectra. In the mixture experiment, the acquired data were examined using principal components analysis (PCA) and quantified by partial least square regression (PLS-S) with Unscrambler X software. The TRSr showed a relatively high resolution, high SNR, fluorescence for some materials, and penetration depth for BA up to 5.90 mm. Characterization of BA was successfully performed. Also, it was possible to acquire spectra when BA was inside other materials, but some were damaged. The discrimination of BA and Sodium Citrate dihydrate (SCD) mixture was possible using the Raman spectra, PCA and PLS-R. For a proof of concept, it was possible to build a model for quantification. Validation of Predicted vs. Reference and Calibration of Predicted vs. Reference plots for responses in (%) BA/SCD tablets showed highly linear responses. TR spectra of liquids compounds were compared satisfactorily with Raman spectra obtained in conventional or backscattering mode found in literature.