Simultaneous measurement of two compounds in aqueous solution with dual quantum cascade laser absorption spectroscopy

Two pulsed Fabry–Pérot quantum cascade lasers (QCL) have been employed for the simultaneous measurement of two analytes in aqueous solutions. Two laser beams (1393 and 1080 cm^-1) were combined by an optical system of parabolic mirrors and a ZnSe-beam splitter. Measurements were made in transmission using a 41 μm CaF₂-flow cell and a mercury-cadmium-telluride (MCT) detector. Using glucose and sodium acetate as model analytes, the measurements show the potential of dual QCL absorption spectroscopy for analyte specific detection and background compensation. The use of the two lasers gives quantitative information about the analytes, even when they show overlapping absorption bands typically found in condensed phase. PACS 42.55.Px; 42.62.Fi