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Analytical applications of vibrational spectroscopy   : study of saccharides by terahertz spectroscopy and application of interband cascade laser to methane by mid-infrared  

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Author(s):
Igor José Gomes da Silva
Total Authors: 1
Document type: Doctoral Thesis
Institution: Universidade Estadual de Campinas, Instituto de Química
Defense date:
Advisor: Ivo Milton Raimundo Junior
Abstract

This thesis describes analytical applications of THz spectroscopy and the development of a sensor for methane in the mid-infrared region based on an interband cascade laser (ICL). For the first part of this thesis, a THz-TDS spectrometer (terahertz time domain spectroscopy) with ASOPS technology (asynchronous optical sampling) was employed, aiming to explore the potential of the technique and to develop analytical applications for the identification of some saccharides. Analytical curves with good sensitivities were obtained in the concentration range from 1.7 to 11.7 (w/w) and the characteristic peaks used for each sugar for univariate calibrations were the following: fructose (1.70 THz), sucrose (1.82 THz), glucose (1.43 THz), lactose (1.37 THz), saccharin (2.66 THz) and sucralose (2,21 THz). Limits of detection were around to 1.0% (m/m). Samples of sweeteners containing sucralose and powdered juices were characterized by the technique, however, quantitative analysis is still a challenge, since the crystallinity of the analyte is important for the analyzes in the THz domain. Peak deconvolution was also employed as a tool to aid in the identification of components in mixtures and it was observed that the region between 0.5 and 2.0 THz is more adequate for such analyzes since scattering is less evident. It was observed that in a mixture of sucrose, glucose and lactose [5% or 10% (m/m) each] in the range of 1.31 to 1.51 THz some sub-peaks of pure lactose and glucose can be identified. In addition, the multivariate curves resolution method was also employed in the analysis of 7 mixtures (lactose, fructose and sucrose), in which the relative error ranged from 0.7 to 26.7%. In a second moment, it was developed a sensor for methane using a new compact light source - laser interband cascade (ICL) ¿ and a new compact gas cell, called substrate-integrated hollow waveguide (iHWG). The methane absorption line that is located between 3,367 and 3,370 ?m is free of interference from other atmospheric gases and has been selected as the target region. In addition, this selected line allowed the operation of the sensor at atmospheric pressure, avoiding the use of a vacuum pump. The analytical curve was linear from 100-2000 ppmv, with correlation coefficient of 0.999989 (r) and detection limit of 38 ppmv. The robustness of the sensor was verified by the Allan variance and the results showed that sensor precision is 0.62 ppbv for 1 s of averaging time and can be further improved to a minimum noise level of around 0.062 ppbv in 256 s of averaging, thereby rendering this sensor concept useful for in-line and on-site emission monitoring and process control applications (AU)

FAPESP's process: 08/57808-1 - National Institute of Advanced Analytical Science and Technology
Grantee:Celio Pasquini
Support type: Research Projects - Thematic Grants