Development of a breadboard co2 laser photoacoustic toxic vapor monitor

Résumé du livre

This report describes the development of a breadboard version of CO2 laser photoacoustic detector. The CO2 laser photoacoustic technique has been demonstrated to be capable of detecting, with high specificity, a variety of toxic compounds a low parts-per-billion (ppb) levels in multicomponent air samples. The technique can be used for monitoring trace levels of various hazardous compounds in ambient air samples. Key achievements during the program included: (1) The determination of CO2 laser absorption cross-section data or seven compounds of EPA concern that are volatile constituents of hazardous chemical waste. These data show that the laser photoacoustic method could detect these compounds in the ambient air at levels well below their most stringent threshold limit values. (2) the development of an acoustic-frequency-tracking device that allows the use of a resonant photoacoustic cell for the first time under field conditions of changing temperature and humidity. (3) The identification of nonadsorptive materials for use in air sampliong[sp] lines and for coating the cell's interior to minimize sample adsorption and reaction losses. (4) The development of a pyro-electronic device that automatically determines the wave-length of a CO2 laser transition. This device allows laser-wavelength selection to be under closed-loop control. (5) the placement of the breadboard detector under microcomputer control such that all wavelength selection and the calculation and display of the unknown concentrations of the gases in the air sample are automatic. (6) the analysis of laboratory-prepared air mixtures to determine the performance capability of the instrument. Experiments on the laboratory-prepared mixtures showed that the fully automatic breadboard instrument can detect hydrazine, a toxic rocket fuel used by the Air Force, at concentrations as low as 5 ppb in the presence of three interfering gases at concentrations as much as 600 times greater.