Water-content analysis by photothermal spectrometry with a near-infrared diode laser

Photothermal spectrometry for water is described in which high-power diode laser with a wavelength coincident with strong vibrational overtone absorption in a near-infrared region was used, In the thermal lens technique, an apparatus consisting of only solid-state devices, such as optical fibers, a fiber-coupler and photodiode, was used. The optical fibers acted as not only optical paths, but also as colliniation devices. A water content of 0.15% in acetonitrile could be detected, and a linear analytical curve was obtained in the range of 0% similar to 7% with a 1478 nm, 100 mW diode laser at an intensity modulation frequency of 20 Hz. A photoacoustic technique could be also applied to water in acetonitrile and water adsorbed on molecular sieves by using a cell equipped with a cylindrical piezoelectric ceramic. These techniques can be a versatile water-analysis tool for the process monitoring and control.