We report herein the detection of liquid water dissolved in a variety of solvents using a thermoelectrically cooled, pulsed, Fabry–Perot quantum cascade laser, operating at 5.629 μm at room temperature. The prototype sensor system consisted of the laser, a series of off-axis parabolic mirrors, and two mercury cadmium telluride detectors. When applied to the detection of water in tetrahydrofurane, a limit of detection of 0.85 parts per million was achieved. It is envisaged that such a sensor would be well suited to process control applications within the pharmaceuticals industry.
Vol. 4, Iss. 2 Virtual Journal for Biomedical Optics
A. Ouvrard, K. O'Dwyer, and B. D. MacCraith, "Sensing of Water Dissolved in Solvents Using a 5.629 μm Multimode Quantum Cascade Laser," Appl. Spectrosc. 62, 1349-1353 (2008)