[Zurück]

S Schaden, A. Domínguez-Vidal, B. Lendl:
"Quantum cascade laser modulation for correction of matrix-induced background changes in aqueous samples";
Applied Physics B - Lasers and Optics, 86 (2007), S. 347 - 351.

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 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 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. A flow injection
setup was employed to produce carbon dioxide standards 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 (0-90 g/l) of sugar were alsomixed on
line with the analyte to study their influence on carbon dioxide
measurement. As the difference in the two evaluated wavelengths
is small compared to the absorption peak of CO2, the
analytical readout of the QCL modulation can be seen as a proportional
parameter to the first derivative of FTIR spectra in this
spectral region.