A setup is reported for molecular analysis of ultrapure volatile substances based on absorption two-channel computerized IR spectrometry with pulsed tunable injection lasers operating within the wavelength range from 4 to 12 microns. The setup is equipped with a heated vacuum system for gas supply and for gas mixtures preparation. Analytic characteristics are estimated in case of water detection in oxygen, argon, and monogermane; the detection limit is 8 x 10 exp -7 vol pct, 4 x 10 exp -7 vol pct, and 4 x 10 exp -7 vol pct, respectively.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.