Validation of QCL CF4 Gas Analyzer for Sensitivity and Selectivity

Abstract

Quantum cascade lasers (QCL) has open the mid-infrared (mid-IR) spectral range for laser gas monitors. For perfluorocarbon gases (PFCs) such as CF4, continuous emission monitors are now commercially available. Since these instruments can only make use of a narrow IR band, spectral interference from other gas species is not easily resolved. In this paper a commercial QCL CF4 analyser is validated with respect to sensitivity and selectivity. In the laboratory, the laser was mounted on a 0.3-m measurement cell. A gas mixer provided humidified gas mixtures of CF4 and methane. The results indicated that while there was no interference from water in the range up to 8000 ppm H2O, a small interference from methane was observed. This was quantified to be approximately 3 ppb CF4 per ppm of methane. The sensitivity of the instrument was found to be 10.5 ppb CF4 for one-meter light path.