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16. Chemically Modified Silica
gel with DETA-Silane as Bonded Stationary Phase for Gas-Solid
Chromatography - A Theoretical and Practical Approach
Prachathipat Pongpinyo, Wirach Wongphattanagul, Sunantha Hengrasmee
and Saksit Chanthai*
Department of Chemistry, Faculty of
Science, Khon Kaen University,Khon Kaen 40002, Thailand
Abstract:
A chromatographic silica gel (40-63
mm
dp) was chemically modified with DETA-silane, 3-[2-(2-aminoethylamino)
ethylamino] propyltrimethoxysilane, at various concentrations between
3% and 20% (v/w). Specific surface areas of the unmodified silica and
the DETA-modified silica determined by methylene blue adsorption
isotherm were 103.20 and 2.02 m2 g-1,
respectively. The surface area of the DETA-modified silica was
therefore very much smaller than the unmodified silica because of the
DETA-functional groups. This study was succeeded in linking DETA-silane
at concentration 3% and 5% (v/w) to silica gel. The modified silica
has excellent thermal stability and was used as stationary phase for
gas chromatography with 3 g of the modified silica which was packed in
a borosilicate glass column (50 cm x 3 mm i.d.) and the actual
stationary phase was 30 cm long. The column performance and efficiency
was evaluated according to the van Deemter equation. Using 5% DETA-modified
silica with 60-80 mesh in particle size gave satisfactory separation
of mixed aliphatic alkanes (C6-C11) within 23
minutes under optimum conditions. The obtained results were good in
the separation of these hydrocarbons with the resolution ranges of
each coupled peaks of the aliphatic alkanes between 0.97-2.31 and
0.88-2.04 for 3% and 5% DETA-modified silica, respectively, when
compared to those of the unmodified silica (0.30-1.67). Therefore, the
modified silica can satisfy the need for an efficient basic stationary
phase for such a manually packed column in gas-solid chromatography.
Key words:
silica gel, bonded phase,
surface area, adsorption isotherm, aliphatic alkane, gas-solid
chromatography. van Deemter equation
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