Can High-Pressure Raman Spectroscopy Be Simplified? A Microscale Optical-Fiber Capillary Cell for the Study of Supercritical Fluids

Abstract

This paper reports the design of a simple and inexpensive optical fiber capillary flow cell which is ideally suited to Raman spectroscopy and, in particular, the analysis of high-pressure supercritical fluid solutions. Light is delivered directly to the solution by use of optical fibers which run along the bore of the capillary. For maximum efficiency of light collection, the capillary is mounted directly onto and along the axis of the entrance slit of a dispersive Raman spectrometer. The Raman spectra of supercritical carbon dioxide (scCO2) solutions of gases (e.g., nitrogen and hydrogen), and solid solutes (e.g., naphthalene) are presented.

On-line polymerisation monitoring in scCO2: a reliable and inexpensive sampling method in high pressure applications

“…As with IR spectroscopy and turbidimetry, Raman spectroscopy requires the incorporation of a window into the body of the reactor for incident light interaction with the reaction medium. While Raman spectra can be captured at location of the incident light, avoiding the need for a fixed path length or second window [41], the overall cost of such a setup forms a barrier to widespread implementation. An on-line monitoring technique that does not require the incorporation of windows or probes into the reactor setup is power compensation calorimetry [42][43][44][45].…”

Enhanced spontaneous Raman scattering and gas composition analysis using a photonic crystal fiber

“…It is noted that classical hollow capillary tubes have also been used for the enhancement of nonlinear optical interactions [5][6][7][8][9][10][11][12][13]. These capillaries work best with rays that propagate at grazing incidence, i.e., when only the fundamental EH 11 or low-order waveguide mode propagates [14][15][16][17][18].…”

“…Thus these experiments are not strongly affected by the requirement of grazing incidence. There have, however, been reported enhancements of spontaneous Raman signals using hollow-core capillary tubes for collinear propagation of pump and Stokes signals [10,13]. The Stokes signals generated therein depend linearly on the number of modes that propagate to the output of the tube with low loss.…”

Vibrational Spectroscopy

“…A series of miniature vessels has been designed [24,25] for Raman spectroscopy including a microscale version based upon a short length of silica capillary (Figure 3.1-2), which provides a convenient method for monitoring Hz in the photochemical flow reactor. A series of miniature vessels has been designed [24,25] for Raman spectroscopy including a microscale version based upon a short length of silica capillary (Figure 3.1-2), which provides a convenient method for monitoring Hz in the photochemical flow reactor.…”