[Zurück]

N. Leopold, M. Haberkorn, T. Laurell, J. Nilsson, J Baena, J. Frank, B. Lendl:
"On-Line Monitoring of Airborne Chemistry in Levitated Nanodroplets: In Situ Synthesis and Application of SERS-Active Ag-Sols for Trace Analysis by FT-Raman Spectroscopy";
Analytical Chemistry, 75 (2003), S. 2166 - 2171.

We report a new strategy for on-line monitoring of chemical
reactions in ultrasonically levitated, nanoliter-sized
droplets by Raman spectroscopy. A flow-through microdispenser
connected to an automated flow injection system was used to dose picoliter droplets into the node of an ultrasonic trap. Taking advantage of the flow-through characteristics of the microdispenser and the versatility of the automated flow system, a well-defined sequence of reagents could be injected via the microdispenser into the
levitated droplet placed in the focus of the collection optics
of the Fourier transform Raman spectrometer. In that way,
chemical reactions could be carried out and monitored
on-line. The developed system was used for fast, reproducible,
in situ synthesis of a highly active surface
enhanced Raman scattering (SERS) sol resulting from the
reduction of silver nitrate with hydroxylamine hydrochloride
in basic conditions. With this chemical system, SERS
substrate preparation could be achieved at room temperature
and in short time. The in situ prepared silver sol
was used for trace analysis of several organic test molecules
that were injected into the levitated SERS-active
droplet again using the microdispenser. The concentration
dependence of the SERS spectra was studied using
9-aminoacridine, revealing that down to the femtogram
region high-quality SERS spectra could be obtained.
Additionally, SERS spectra of 6-mercaptopurine, thiamine,
and acridine were recorded in the levitated drop as well.

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