Laser-induced fluorescence for PAH determination
Over the last decade, our team developed different versions of a transportable UV-laser-fluorimeter with fibre optical probe for use in environmental and process analysis.
As light source a short-pulse up-converted diode-pumped Nd:YAG-laser with emission at 266 nm is used. The wavelength is perfect for the excitation of mono- (BTXE) and polycyclic aromatic hydrocarbons (PAH), as well as humic substances, aromatic amino acids and proteins.
Deploying optical waveguides out of quartz, the laser pulse is flexible guided to the measurement place for the excitation and the fluorescent emission is then guided back to the detection unit. Due to the special geometry of the fibres in the probe, the emission is collected efficiently and the entry of directed stray light is minimized.
The detection was implemented in different ways:
Time-dependent sequential, lifetime-resolved detection:
The fluorescence emission is spectrally fragmented and the spectra are detected at different times after the excitation pulse is emitted with a gated, intensified CCD-camera. Out of the obtained data, the spectrometer software builds up an emission-decay-spectrum.
Wavelength-dependent sequential, lifetime-resolved detection:
By applying a monochromator, a single emission wavelength can be chosen for which a high temporal resolved fluorescence decay curve can be detected. This is possible in deploying a time-correlated single photon counting technique. Out of several decay curves the software builds up an emission-decay-spectrum.
Integral fluorescence detection:
In combination with a diode line or CCD line array, the full fluorescence emission spectrum can be obtained. This setup is used, if the fluorescence decay times in the application are shorter than the decay of the instrument response function.
The control of all system versions is implemented with a self-developed spectrometer software. Furthermore, with this software a qualitative and quantitative data evaluation is feasible that ranges from simple linear one-component-regression over decay-time analysis to complex multi-component-analysis by deploying chemometric methods.
For feasibility studies the laserfluorimeters are placed at interested party’s disposal.
F. Lewitzka, M. Niederkrüger, G. Marowsky:
„Application of Two-Dimensional LIF for the Analysis of Aromatic Molecules in water”, in P. Hering, J.P. Lay, S. Strey (Editors): „Laser in Environmental and Life Sciences”, 141-161, Springer Verlag, Berlin, 2003.
P. Karlitschek, F. Lewitzka, U. Bünting, M. Niederkrüger, G. Marowsky:
„Detection of aromatic pollutants in the environment using UV-laser-induced fluorescence“, Appl. Phys. B 67, 497-504, 1998.
DBU-Förderung „Entwicklung eines Laserfluorimeters zum Nachweis von organischen Schadstoffen in Wasser“ (1994-1996, Förderkennzeichen 01989).
BMBF-Förderprogramm Mikrosystemtechnik „BTXE und PAK Sensor“ (1996-1999, Förderkennzeichen 16SV558/0).
BMBF-Förderprogramm Mikrosystemtechnik „BTXE und PAK Sensor II“ (1999-2003, Förderkennzeichen 16SV1112/5).
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Laser-Laboratorium Göttingen e.V. (LLG)
Head of Department
Dr. Hainer Wackerbarth
"Photonic Sensor Technologies"