Depolarization ratio of the ν1 Raman band of methane at different environment

The work is aimed at measuring the depolarization ratio of the ν1 Raman band of methane in nitrogen and carbon dioxide media at a pressure of 50 atm. To improve the accuracy of estimating the ν1 intensity in the depolarized spectrum, we used the simulation of the ν3 band. It was found that the environment of nitrogen and carbon dioxide has a negligible effect on the depolarization ratio of the ν1 Raman band of methane

Possibilities of measuring the exhaled air composition using Raman spectroscopy

A Raman spectrometer for gaseous media with a detection limit at a level of 100 ppb is developed. The results of its experimental approval on exhaled air samples from healthy people confirmed the possibility of monitoring the concentrations of a number of hydrocarbon compounds and 13CO2. The ways of further development of this analytical method are outlined

Multipass Raman gas analyzer for monitoring of atmospheric air composition

An improved gas analyzer based on Raman spectroscopy is presented. The device can measure the content of all molecular species of atmospheric air, whose concentration exceeds the sensitivity threshold. To obtain a high signal-to-noise ratio, a multi-pass optical system for scattering excitation was used together with the compression of the analyzed gas sample to a pressure of 20 atm. A technique for deriving concentrations from Raman spectra of atmospheric air based on the contour fit method is described. At the working pressure, a good agreement between the measurements of the daily air concentration of the carbon dioxide (CO2) and methane (CH4), and the data obtained with a high-sensitive CRDS gas analyzer was obtained. The standard deviation of the measured CH4 concentration values was ~ 20 ppb. Estimates are given for the detection limits of the most common gas impurities in air, as well as for the Raman scattering cross sections for formaldehyde (CH2O), benzene (C6H6), and toluene (C7H8) vapor

Development of Raman gas analyzers at IMCES SB RAS

Gas analyzers on the basis of Raman spectroscopy designed at the Institute of Monitoring of Climatic and Ecological Systems, Siberian Branch, Russian Academy of Sciences, are described. Their capabilities and advantages are shown in measurements of the composition of fuel gases (natural, bio-, and synthesis gases) and atmospheric and exhaled air. The features of the analyzer operation and the techniques for increasing the measurement accuracy are discussed

Raman natural gas analyzer: Effects of composition on measurement precision

Raman spectroscopy is a promising method for analyzing natural gas due to its high measurement speed and the potential to monitor all molecular components simultaneously. This paper discusses the features of measurements of samples whose composition varies over a wide range (0.005-100%). Analysis of the concentrations obtained during three weeks of experiments showed that their variation is within the error caused by spectral noise. This result confirms that Raman gas analyzers can operate without frequent calibrations, unlike gas chromatographs. It was found that a variation in the gas composition can change the widths of the spectral lines of methane. As a result, the measurement error of oxygen concentration can reach 200 ppm. It is also shown that neglecting the measurement of pentanes and n-hexane leads to an increase in the calculated concentrations of other alkanes and to errors in the density and heating value of natural gas