(538c) Monolithic Columns Modified with Ag Nanoparticles for TLC Separations of Fatty Acids

Lipids are a very
broad class of biologically relevant compounds, encompassing fatty acids (FA)
and their derivatives, as well as substances biosynthetically related to FA.
The separation and detection of FA is a key issue for medical diagnostics, as
certain FA are associated with pathological conditions, as well as for the food
industry, particularly for the hydrogenation of food oils.¹ The
separation of FA is traditionally performed by silver-ion chromatography, using
stationary phases for column or thin-layer chromatography (TLC), impregnated or
modified with Ag ions. The interaction between Ag ions and the unsaturated
moieties of FA modulates the separation, on the basis of the number and
configuration of the FA double bonds.²

Recent
computational studies have suggested that Ag nanoparticles (NP) may exhibit a
similar type of interaction, which could be utilized for the separation of
olefinic molecules.³ Therefore, stationary phases modified with Ag
NP could efficiently perform FA separations, without the disadvantages of Ag
ions, such as ?bleeding-in? by polar solvents or high sensitivity to light,
moisture and mild reducing environments.

To this end, we
have prepared polymer monoliths in a thin-layer format⁴ and
functionalized them uniformly with Ag NP. Such monoliths are indeed able to
perform TLC separations of free FA, according to the number of their double
bonds (see Figure 1). The effect of the mobile phase composition on the FA
retention and selectivity has been investigated. Owing to the flat format of
our monoliths, the detection is achieved by Matrix-Assisted Laser Desorption
Ionization Mass Spectroscopy (MALDI-MS), by performing automated scans directly
on the developed TLC plates. Moreover, Ag NP are able to substitute the
function of conventional MALDI matrixes, which are substances that typically need
to be additionally applied in order to enable the desorption/ ionization of the
analytes towards the MS detector. Thanks to the presence of Ag NP, the
detection of FA is made possible from our TLC monoliths immediately after
separation.

 Figure 1. MADLI scan along a single lane on a TLC monolithic
plate, functionalized with Ag NP, where FA separation has been achieved; the
number of carbon atoms and double bonds is denoted at the positions of the
respective FA; development time: 1 min 10 s  

1. Fuchs B. et al., Journal of Chromatography A 1218 (2011)
2754

2. Nikolova-Damyanova B. et al., Journal of Liquid Chromatography
& Related Technologies 24 (2001) 1447

3. Pozun Z. et al., Journal of Physical Chemistry C 115
(2011) 1811

4. Bakry R. et al., Analytical Chemistry 79 (2007) 486