Methods of Elimination of Water Vapor Bands from an Infrared Spectrum

Water vapor absorption bands may severely obscure important sample features in the infrared spectrum.In order to solve this problem,many methods,such as,vacuum,dry air purging technique,sample shuttle technique and spectral subtraction,etc,have been proposed and conducted.In this article,humidity titration method to remove water vapor noise completely was emphatically reviewed.The scanning procedure of a sample single beam spectrum was divided into two stages.At the first stage,the appearance of water vapor peaks was allowed and the absorption direction(for example absorbance A≥0 or A≤0) of water vapor bands was observed easily at the end of this stage.Then,the relative humidity in the sample compartment of spectrometer was changed by a dry or a wet air supply depending on the absorption direction of water vapor bands.After the relative humidity was changed to a certain extent,water vapor peaks would become smaller and smaller with the increase in scanning number during the second stage.By this way,water vapor noise could be eliminated progressively and completely at last.