Determination of nitrogen dioxide by pulsed thermal lens spectrophotometry

Abstract

A thermal lens spectrophotometric system, consisting of a pulsed dye laser source, a photomultiplier, and a wave memory controlled by a microcomputer, is used for a determination of atmospheric NO/sub 2/. The enhancement factor for the sample in various media is calculated by using the theoretical equation and the optical parameters and compared with the observed value for the gaseous and liquid phase samples. The agreement of the observed value with the theoretical value was fair. For a laser pulse energy of 1 mJ, a signal enhancement of 10/sup 3/ is expected in comparison with a conventional spectrophototmeter. The determination of NO/sub 2/ is carried out by using a dye laser with a pulse energy of 20-40 ..mu..J, and a detection limit of 0.8 ppm was achieved. Verification of the theorectical equation and advantages of a pulsed laser source for the determination of the gaseous sample are discussed in comparison with a CW laser excitation method. 3 tables, 2 figures.