title: Near-infrared measurement of relative and absolute humidity through detection of water adsorbed on a silica gel layer.
abstract: Near-IR spectroscopy is especially well suited to moisture determination because of the relatively high absorptivity of water compared to most other substances. In the present work, near-IR diffuse-transmittance spectroscopy is applied to the measurement of humidity via observation of adsorbed water on a high-performance thin-layer chromatography silica gel plate. The adsorbed water is detected through both ordinary absorption of radiation by water molecules and the increased scattering of near-IR radiation by the silica gel as it adsorbs more water. This technique shows promise as a highly accurate and sensitive humidity sensor with a time constant of less than 1 min. The addition of inorganic salts to the silica gel layer is shown to increase the response to water vapor. However, it also increases the time constant of the sensor. A miniature humidity sensor using a commercially available near-IR transmissive switch is also demonstrated. Possible interferences and hysteresis effects are investigated.
authors.affiliation: Department of Chemistry, Indiana University, Bloomington 47405.
authors.forename: A
authors.initials: A
authors.lastname: Fong
authors.forename: G M
authors.initials: GM
authors.lastname: Hieftje
mesh_terms: D000327:Adsorption; D002138:Calibration; D002855:Chromatography, Thin Layer; D006813:Humidity; D012822:Silicon Dioxide / Q000737:chemistry; D013055:Spectrophotometry, Infrared; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water; D012822:Silicon Dioxide