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