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B. Lendl:
"Quantitative analysis in liquid phase using quantum cascade lasers";
Vortrag: The 2nd International Workshop on Quantum Cascade Lasers, Ostuni, Italy (eingeladen); 06.09.2006 - 09.09.2006.

There are a number of applications in chemical analysis of liquids where quantum cascade
lasers could be used advantageously. QCL detection can be used in dedicated sensor systems
as well as in standard techniques of chemical analysis such as chromatography,
electrophoresis or flow injection analysis.
Whereas advantages in gas phase detection gained by QCL technology are evident due to the spectral match of sharp emission lines with the ro-vibrational absorption lines of the analytes, important advantages for compact sensor development may also be seen in the use of QCL technology for the analysis of liquids. In condensed phase spectroscopy one has to face strong solvent absorption as well as broad (FWHH of typically 10-40 cm-1) and partly overlapping
absorption bands. The strong solvent absorption usually constrains the applicable optical path
lengths for absorption measurements to a few microns (typically 8-30 μm in aqueous phase)
which limits sensitivity and robustness of possible sensor systems. Due to the high spectral
power density of QCLs significantly longer optical paths can be realized (up to 200 μm or
longer) which substantially improve robustness and sensitivity of possible sensor systems.
The difficulty of spectral overlap of absorption bands or changing background solvent
absorption due to sample-solvent interactions in liquid phase can be solved by taking
advantage of the increasing tuning range in QCL technology.
On the example of the determination of carbon dioxide in sugar containing solutions, it will
be exemplified how a controlled modulation of the laser emission line of less than one
wavenumber allows quantitative, interference free determination of carbon dioxide in aqueous
phase.