Assessment of quantum cascade lasers as mid infrared light sources for measurement of aqueous samples

摘要

The potential of Fabry Perot Quantum Cascade (QC) lasers for transmission measurements of aqueous samples was assessed. For this purpose two lasers, one lasing in the region of the bending vibration of water at 1650 cm(-1), and the other in the water window at 1080 cm(-1), were used in a flow injection system comprising a dedicated fibre-optic flow cell with an adjustable path length. As test analytes a nucleic base (adenine) and a nucleoside (xanthosine) were used. Compound-specific information was obtained as the nucleoside contained a carbohydrate unit in addition to the heteroaromatic ring structure. With the laser emitting at 1650 cm(-1) the heteroaromatic ring structure of both compounds gave rise to flow injection peaks, whereas, only the nucleoside, containing the C-O stretching vibrations of the carbohydrate unit, produced peaks also with the laser emitting at 1080 cm(-1). The path length limitations were investigated for both lasers. For the 1650 cm(-1) laser, path lengths up to 59 mum could be used, despite the strong absorption of water. For xanthosine analysis, the limit of detection (S/N = 3) at this path length was determined to be 0.07 g l(-1). Optical path lengths of up to 150 mum could be used for the laser emitting at 1080 cm(-1). (C) 2002 Elsevier Science B.V. All rights reserved. [References: 12]