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Evaluation of spurious results in the infrared measurement of CO2 isotope ratios due to spectral effects: a computer simulation study

Evaluation of spurious results in the infrared measurement of CO2 isotope ratios due to spectral effects: a computer simulation study
Evaluation of spurious results in the infrared measurement of CO2 isotope ratios due to spectral effects: a computer simulation study
The application of infrared spectroscopy to the measurement of carbon isotope ratio breath tests is a promising alternative to conventional techniques, offering relative simplicity and lower costs. However, when designing such an instrument one should be conscious of several spectral effects that may be misinterpreted as changes in the isotope concentration and which therefore lead to spurious results. Through a series of computer simulations which model the behaviour of the CO2 absorption spectrum, the risk these effects pose to reliable measurement of 13CO2=12CO2 ratios and the measures required to eliminate them are evaluated. The computer model provides a flexible high-resolution spectrum of the four main isotopomer fundamental transitions and fifteen of their most significant hotband transitions. It is demonstrated that the infrared source, infrared windows and breath sample itself all exhibit strong temperature-induced errors but pressure effects do not produce significant errors. We conclude that for reliable measurement of 13CO2=12CO2 ratios using infrared spectroscopy no pressure controls are required, window effects are eliminated using windows wedged at a minimum angle of 0.8-2.2 mrad, depending on the material, and the temperature sensitivity of source and gas cells necessitates stabilization to an accuracy of at least 0.2 K.
0031-9155
1155-1167
Mansfield, C.D.
2354cf62-85aa-497f-8a77-b0705e608bf3
Rutt, H.N.
e09fa327-0c01-467a-9898-4e7f0cd715fc
Mansfield, C.D.
2354cf62-85aa-497f-8a77-b0705e608bf3
Rutt, H.N.
e09fa327-0c01-467a-9898-4e7f0cd715fc

Mansfield, C.D. and Rutt, H.N. (1999) Evaluation of spurious results in the infrared measurement of CO2 isotope ratios due to spectral effects: a computer simulation study. Physics in Medicine and Biology, 44 (5), 1155-1167. (doi:10.1088/0031-9155/44/5/004).

Record type: Article

Abstract

The application of infrared spectroscopy to the measurement of carbon isotope ratio breath tests is a promising alternative to conventional techniques, offering relative simplicity and lower costs. However, when designing such an instrument one should be conscious of several spectral effects that may be misinterpreted as changes in the isotope concentration and which therefore lead to spurious results. Through a series of computer simulations which model the behaviour of the CO2 absorption spectrum, the risk these effects pose to reliable measurement of 13CO2=12CO2 ratios and the measures required to eliminate them are evaluated. The computer model provides a flexible high-resolution spectrum of the four main isotopomer fundamental transitions and fifteen of their most significant hotband transitions. It is demonstrated that the infrared source, infrared windows and breath sample itself all exhibit strong temperature-induced errors but pressure effects do not produce significant errors. We conclude that for reliable measurement of 13CO2=12CO2 ratios using infrared spectroscopy no pressure controls are required, window effects are eliminated using windows wedged at a minimum angle of 0.8-2.2 mrad, depending on the material, and the temperature sensitivity of source and gas cells necessitates stabilization to an accuracy of at least 0.2 K.

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Published date: May 1999
Organisations: Optoelectronics Research Centre

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Local EPrints ID: 77754
URI: http://eprints.soton.ac.uk/id/eprint/77754
ISSN: 0031-9155
PURE UUID: 8d989ab5-763c-4999-bdaa-1cbdd9fbfc16

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Date deposited: 11 Mar 2010
Last modified: 19 Jul 2018 16:31

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Contributors

Author: C.D. Mansfield
Author: H.N. Rutt

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