Measurement of Water Vapor Pressure and Activity Using Infrared Diode Laser Absorption Spectroscopy
| Autor: | S. A. Johnson, Paul B. Davies, P. G. Cummins, S. A. Bone |
|---|---|
| Rok vydání: | 1993 |
| Předmět: |
Tunable diode laser absorption spectroscopy
Absorption spectroscopy business.industry Chemistry Vapor pressure 010401 analytical chemistry Vapour pressure of water Analytical chemistry Laser 01 natural sciences 0104 chemical sciences law.invention 010309 optics Optics Pressure measurement law 0103 physical sciences business Absorption (electromagnetic radiation) Instrumentation Spectroscopy Water vapor |
| Zdroj: | Applied Spectroscopy. 47:834-843 |
| ISSN: | 1943-3530 0003-7028 |
| DOI: | 10.1366/0003702934066947 |
| Popis: | A mid-infrared laser technique is described for the accurate determination of water vapor concentration in the headspace above a liquid sample. The method is based on the measurement of the fractional absorption, at line center, of a single ro-vibrational line. A dual-beam optical arrangement, incorporating a reference vapor cell, is used to provide an active calibration for the measurement. It is shown how the absorption signals can be related to the water activity of a liquid sample. The technique has the advantages of being noninvasive, rapid, and signal-specific to water. It does, however, intrinsically have a nonlinear response to activity. This drawback is mainly a consequence of pressure broadening, and has limited the present measurements to sample temperatures in the range 268 to 293 K. In this regime the method gives a precision of ±1% for activities near unity. This limit is imposed by small fluctuations in certain environmental variables. Suitable modifications should enable operation at the ±0.1% level of accuracy over an extended temperature range. |
| Databáze: | OpenAIRE |
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