Analysis and Classification of Liquid Samples Using Spatial Heterodyne Raman Spectroscopy. Issue 12 (December 2019)

• Record Type: Journal Article
• Authors: Gojani, Ardian B.; Palásti, Dávid J.; Paul, Andrea; Galbács, Gábor; Gornushkin, Igor B.
• Is Part Of: Applied spectroscopy. Volume 73:Issue 12(2019)
• Page Start: 1409
• Page End: 1419
• Publication Date: 2019-12
• Subjects: Spatial heterodyne spectroscopy -- Raman spectroscopy -- diode-pumped solid-state -- DPSS -- chemical analysis; Spectrum analysis -- Periodicals; 543.505
• DOI: 10.1177/0003702819863847
• Languages: English
• ISSNs: 0003-7028

Abstract

Spatial heterodyne spectroscopy (SHS) is used for quantitative analysis and classification of liquid samples. SHS is a version of a Michelson interferometer with no moving parts and with diffraction gratings in place of mirrors. The instrument converts frequency-resolved information into a spatially resolved one and records it in the form of interferograms. The back-extraction of spectral information is done by the fast Fourier transform. A SHS instrument is constructed with the resolving power 5000 and spectral range 522–593 nm. Two original technical solutions are used as compared to previous SHS instruments: the use of a high-frequency diode-pumped solid-state laser for excitation of Raman spectra and a microscope-based collection system. Raman spectra are excited at 532 nm at the repetition rate 80 kHz. Raman shifts between 330 cm −1 and 1600 cm −1 are measured. A new application of SHS is demonstrated: for the first time, it is used for quantitative Raman analysis to determine concentrations of cyclohexane in isopropanol and glycerol in water. Two calibration strategies are employed: univariate based on the construction of a calibration plot and multivariate based on partial least squares regression. The detection limits for both cyclohexane in isopropanol and glycerol in water are at a 0.5 mass% level. In addition to the Raman–SHS chemical analysis, classification of industrial oils (biodiesel, poly(1-decene), gasoline, heavy oil IFO380, polybutenes, and lubricant) is performed using the Raman–fluorescence spectra of the oils and principal component analysis. The oils are easily discriminated showing distinct non-overlapping patterns in the principal component space.