Chemistry Reference
In-Depth Information
Fig. 45
Δ
RAS spectra
measured for the exposure
of the LB film to a mixture
of analytes A and B after the
inlet of single analytes (A or
B) has been separately
interrupted (
panel
b, after
hexane inlet interruption;
panel
d, after ethanol inlet
interruption). The RAS
spectra of analyte A
(ethanol) and analyte B
(hexane) are reported,
respectively, in
panels
a and
c. The dilution value for
both ethanol and hexane
was 18%. Zero lines have
been reported in all cases
(From Bussetti et al. [
88
].
Reprinted with permission.
Copyright 2011. American
Chemical Society.)
fact allows butylamine to displace both ethanol and hexane from the porphyrin
binding sites, resulting in the nonlinear behavior of
RAS spectra variations when
the film is exposed to mixtures containing butylamine.
The consequence is significant for sensing applications: measuring the signal of
the film for known concentrations of single analytes, the optical anisotropy varia-
tions for VOCs could be listed in a sort of analyte library, to deconvolve into single
components the complex RAS spectrum measured after the sensor has been
exposed to an unknown mixture of those VOCs. More properly, this finding
suggests the possibility to discriminate among volatile compounds according to
the interaction mechanisms that binds the molecule to the porphyrin layer. In the
case illustrated here, for each molecule, a dominant interaction mechanism can be
found: dispersion interaction for hexane and coordination for ethanol. It is impor-
tant to remark that in many other volatile compounds, more than one interaction
mechanism can coexist: the study of the RAS signal in these situations will be the
subject of successive investigations.
Δ
