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A. Domínguez-Vidal, S Schaden, B. Lendl:
"Quantum cascade laser modulation for correction of matrix induced background changes in aqueous samples";
Poster: International Conference on Advanced Vibrational Spectroscopy, ICAVS 4, Corfu; 10.06.2007 - 15.06.2007.

Wavelength tuning of a QCL was successfully applied in liquid phase spectroscopy as a promising tool for compensating background changes. Even if the tuning range of the used QCL was essentially smaller than the absorption band of the analyte, the gained information of two neighboring wavenumbers was sufficient to compensate changes in the water background arising from variations in the matrix. Here, a robust method for the determination of carbon dioxide in sugar-containing solutions using a single distributed feedback quantum cascade laser (QCL) has been developed. By switching the laser driving current between two selected values, 1.6 and 1 A, emission wavelengths at 2341.4 and 2341.6 cm-1 could be achieved.
The proposed method is based on absorbance measurements in transmission and the calculation of the absorbance differences between both wavenumbers. This allows the elimination of indirect matrix interference produced on carbon dioxide measurements with increasing sugar concentrations.
Carbon dioxide standards were prepared in situ by means of a flow injection setup from a series of bicarbonate solutions (0-3 g/l) by adjusting the pH with a sodium hydroxide/citric acid buffer solution to pH 3.13. Different concentrations (0-90g/l) of sugar were also mixed on line with the analyte to study their influence on carbon dioxide measurement.