[Zurück]

S. Laschober, E. Rosenberg:
"Synthesis and Characterisation of Monolithic Capillary Columns using Sol-Gel Synthesis based on Methyl-trimethoxysilane";
Poster: ANAKON 2007, Jena, Deutschland; 27.03.2007 - 30.03.2007.

Interest in monolithic columns for capillary liquid chromatography has grown in recent years [1,2]. Synthesis based on the sol-gel process using teraalkoxysilanes as educts is the most widely used technique in this field. These materials will give a silica surface which has to be fuctionalised in a second step. When using alkyltrialkoxysilanes this last step can be avoided as the surface obtained after the second step is already hydrophobic. First columns based on this type of precursors have recently been reported [3].
Monolithic capillary columns were synthesised employing the sol-gel method based on acidic catalysis using methyltrimethoxysilane as precursor. Experimental conditions such as precursor and solvent ratios, catalyst strength and gelation temperature were investigated and optimised in previos work [4]. Materials obtained possessed pore diameters from 0.8 to 15 µm and xerogel network diameters from 0.4 to 12 µm. Specific surface areas up to 334 m2/g were observed, however many materials possessed areas only in the low m2/g range.
Chromatographic tests based on the protocols developed by Engelhardt, Tanaka and Galushko were performed with the synthesised capillary columns. A HP 1090 system with UV-DAD was used for these tests, employing isocratic conditions for separation. The results show a uniform selectivity between hydrophobic test analytes throughout all investigated columns. Methylene selectivity values obtained from different alkylated benzene derivates are higher than observed for various commercial C18 modified HPLC columns. Absolute retention factors for hydrophobic compounds vary by a factor of 2 between different columns, indicating a difference in the phase ratio, usually a sign of different specific surface areas accessible for interaction with the analytes. Nitrogen adsorption measurements indicated the prevalent existence of micropores which is reflected by the elution of larger compounds such as triphenylene and o-terphenyl in the deadvolume. The inclusion of polymeric porogens into the synthesis could eliminate this effect. Results using polar test compounds indicate a high level of silanol activity with much variation between the columns, which means that aging and drying of synthesised columns have to be optimised to minimise the occurrence of free silanol groups.

[1] E. Klodzinska, D. Moravcova, P. Jandera, B. Buszewski, J. Chromatogr. A 1109 (2006) 51.
[2] N. Tanaka, M. Motokawa, H. Kobayashi, K. Hosoya, T. Ikegami, in F. Svec, T.B. Tennikova, Z. Deyl (Eds.), Monolithic Materials (Journal of Chromatography Library, Vol. 67), Elsevier, Amsterdam, 2003, p. 173.
[3] K. Kanamori, H. Yonezawa, K. Nakanishi, K. Hirao, H.J. Jinnai, J. Sep. Sci 27 (2004) 874.
[4] S. Laschober, E. Rosenberg, M. Sulyok, J. Chromatogr. A, In Press, published online, DOI: 10.1016/j.chroma.2007.01.016.

Projektleitung Egon-Erwin Rosenberg:
Rosenberg - Monolithen