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B. Zachhuber, J. Kuligowski, W. Tomischko, B. Lendl:
"SIMULTANEOUS USE OF TWO QCLs FOR WINE ANALYSIS WITH HPLC AND ON-LINE MID-IR DETECTION";
Poster: 13. Österreichische Chemietage, Wien; 24.08.2009 - 27.08.2009.

Quantum cascade lasers (QCLs) are a new generation of powerful light sources for mid-IR spectroscopy. Due to their high spectral power density, longer optical paths can be realized in transmission measurements as compared when using standard FTIR spectrometers. Therefore, the use of these lasers holds great promise to increase sensitivity in on-line IR detection in high performance liquid chromatography (HPLC), based on transmission measurements. However, due to the general small tuning range of standard QCLs, spectral information is lost when replacing the FTIR spectrometer by a single quantum cascade laser [1]. Here, we report our results obtained by interlacing two different Fabry Pérot QCLs for quasi simultaneous absorption measurements at two different wavelength regions (one centered at 1393 cm-1 for organic acids and the other at 1080 cm-1 for sugar).
Our set-up, based on three gold mirrors and a ZnSe beam splitter, is used to direct the emitted laser light through a liquid flow cell with an optical path length of 100 μm, onto a mercury-cadmium-telluride (MCT) detector.


A gate delay of 300 ns for the first QCL and 200 ns for the second one was selected. For both lasers the pulse repetition rate was set to 25 μs and the pulse length was adjusted to 50 ns.
The voltage output signal of the detector was split and processed by two box car averagers. The QC-laser signals were evaluated separately, setting the gates of each box car averager on one laser pulse. The averaged output signal was connected to an AD-Converter. The digital signal was processed via LabVIEW SignalExpress.
The use of a dual QC-laser system leads to more selective and robust measurement systems as more structural information on the investigated system is obtained. To show the usefulness of the proposed detection system, we employed it for the analysis of eight different components of wine and grape juice samples. On-line dual QC laser detection in HPLC provides detection limits, for example of 0.19 mg/mL for acetic acid, successfully showing detection in the low mg/mL region for the first time.


References
[1] A. Edelmann, C. Ruzicka, J. Frank, B. Lendl, W. Schrenk, E. Gornik and G. Strasser J. Chromatogr. A 934 (2001) 123-128