Trace gas and dynamic process monitoring by Raman spectroscopy in metal-coated hollow glass fibres

Abstract

Quantitative capillary Raman spectroscopy measurements are described, in which improved speed and sensitivity for atmospheric trace gas analysis and real-time monitoring of catalytic hydrogen-exchange reactions were demonstrated. ARTICLE accepted for publicationT.M. James et al -Raman trace gas and process monitoring using metal-coated hollow glass fibres Results on using capillary Raman spectroscopy as an approach for improving the speed, sensitivity and limit of detection for quantitative analysis of gases are reported. Specifically, its potential for trace component identification and rapid process control has been explored. Using a metal-lined hollow glass capillary configuration, its Raman signal was found to be two orders of magnitude larger than that from a conventional 90° Raman implementation. However, the actual improvement in the signal-to-noise ratio and thus the limit of detection was markedly lower, due to an increase in the fluorescence background generated in optical components in the laser beam path and the capillary body itself. Using careful, systematic suppression strategies, the signal-tonoise ratio of our capillary setup increased by a further factor of 3-4, now yielding detection limits for trace gases well below the 100 ppm level. In a "dynamic" measurement series the time evolution of catalytic gas mixing of H 2 and D 2 , to form HD, has been recorded, in which sub-mbar detection limits in sub-second recording times were achieved.

All-in-one: a versatile gas sensor based on fiber enhanced Raman spectroscopy for monitoring postharvest fruit conservation and ripening

“…Experimental setupoptical part Raman gas spectroscopy offers simultaneous detection and quantification of multi-gas mixtures in a wide concentration range from ppm levels up to pure compounds. [26][27][28][29][30][31][32][33] Due to the gas molecule's small Raman cross-sections, typically in the order of 10 −23 cm 2 sr −1 , 34 Raman signals are intrinsically low and need to be enhanced. A novel approach is to use hollowcore photonic crystal fibers 35 (HC-PCF), which act as optical light guide as well as analyte container for the investigated processes gases.…”

Multiple‐pass‐enhanced Raman spectroscopy for long‐term monitoring of hydrogen isotopologues

“…Okita et al demonstrate that the Raman signal can be obtained without a serious decrease of the SNR even if the cell is coiled into a multiple loop with a 3.8‐cm radius . And most recent work at Tritium Laboratory Karlsruhe has reported a LOD for trace gases well below the 100‐ppm level . Besides, their system was tested thoroughly for suitability in tritium environments.…”

Improving the Detection Limit in a Capillary Raman System for In Situ Gas Analysis by Means of Fluorescence Reduction

“…A schematic view of the optical setup of our original capillary Raman setup [ 11 , 12 ] is shown in Figure 1 a. The capillary is a 650 mm long, hollow, silver-lined glass fiber (Doko Engineering, Sendai, Japan), with inner diameter of 1 mm and outer diameter of 1.6 mm.…”

“…For their direct-focusing metal-lined glass capillary setup, Buric et al achieved a 1σ detection limit of 0.12% for N 2 in air at atmospheric pressure, for a one-second measurement interval with a laser power of 150 mW [ 10 ]; this corresponds to a 3σ detection limit of 3.6 mbar. Recently, our group demonstrated the use of a capillary system—based on a metal-lined glass capillary of 650mm length—for dynamic, in situ process monitoring [ 11 ]; and in a system variant suitable for the analysis of tritium-containing, radioactive gases, we were able to detect hydrogen isotopologues with partial pressures of less than 0.5 mbar, for acquisition cycles of 50 × 0.1 s, i.e. , providing composition information every 0.1 s by means of a ‘rolling average’ data evaluation procedure [ 12 ].…”