Analysis and Classification of Liquid Samples Using Spatial Heterodyne Raman Spectroscopy

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.

Determination of broadband-light atomic absorption through interferometric spectrometry with a spatial heterodyne spectrometer

“…This process can reduce the inuence of possible dirt/damage existing on the grating surfaces. Even though this blocking approach is usually recognized as the common practice of SHS, 18,23,25 it is helpless in recovering the unseeable variation induced by narrow-band absorption, where the magnitude of the images is dominated by the broadband feature, as demonstrated throughout this work. Thus, we implemented real-time Fourier transform with a piece of soware built in-house.…”

Comparative Study of Sample Carriers for the Identification of Volatile Compounds in Biological Fluids Using Raman Spectroscopy

“…At this point, it is important to mention that this is the first time in literature that such a carrier and sample preparation method for Raman spectroscopy was designed, proposed, and used for the identification of liquid samples, especially for volatile compounds in biological fluids. Furthermore, the coating of flat microscope slides with gold [ 26 , 53 , 54 ] and the usage of variable types of cuvettes for the Raman analysis of liquid samples [ 36 , 41 , 42 , 43 , 44 ] are referred to in previous studies; however, there is no reference in literature about using as substrate for Raman spectroscopy the cavity of a microscope slide which was coated with gold.…”

“…In most of the cases, the body fluids’ drops had been allowed to dry before their Raman spectra were acquired [ 25 , 26 , 27 , 28 , 29 , 30 , 33 , 34 , 40 ]. Concerning the Raman spectroscopic analysis of liquids and other fluid compounds, glass or quartz cuvettes [ 36 , 41 , 42 , 43 ] and well-sealed glass vessels [ 44 ] have been mentioned as sample holders in a couple of studies. The usage of such substrates could be demonstrated to be beneficial for the effective analysis of volatile compounds, such as ethanol, methanol, acetone, or hydrogen peroxide [ 42 ].…”

Optical modeling of the characteristics of dual reflective grating spatial heterodyne spectrometers for use in laser-induced breakdown spectroscopy

“…For a more detailed description of the SHS principle, please see e.g. [1,7,8]. Further developments and applications of spatial heterodyne spectroscopy mostly came in the astrophysics, planetary exploration and atmospheric spectroscopy fields, in which weak, slowly varying light sources/absorbers/scatterers are observed and a compact, robust spectroscopy instrumentation is very useful [9][10][11][12][13][14][15][16][17].…”

“…Further developments and applications of spatial heterodyne spectroscopy mostly came in the astrophysics, planetary exploration and atmospheric spectroscopy fields, in which weak, slowly varying light sources/absorbers/scatterers are observed and a compact, robust spectroscopy instrumentation is very useful [9][10][11][12][13][14][15][16][17]. Advantages of the application of the SHS concept have already been successfully demonstrated for emission [9][10][11][12]16,17], absorption [18] and Raman spectroscopy [8,14,15,19]. Several modifications of the original SHS optical setup were proposed in the literature, such as the addition of prisms for increased field-of-view [20], a single grating variant for quick tuning [21], an all reflective (also known as cyclic) arrangement [11,12], the incorporation of blazed high-order diffraction grating (Echelle grating) as the beamsplitter and combiner [22], a large aperture static imaging variant (LASIS) [23], and others.…”