SELECTIONGUIDE
RestekCapillaryGCColumnSelectionGuide
Stationary Phase Film Thickness
Stationary phase film thickness affects the retention and elution temperature for each compound
in the sample. A thicker film retains compounds longer, increasing the length of time each
compound spends in the column (
Table1
). A thinner film retains compounds less, reducing the
length of time each compound sp
e column. Very volatile compounds should be
analyzed on a thick film column, to increase the time they spend in the column and allow them
to separate. Highmolecular weight compoundsmust be analyzed on a thin film column, to
reduce analysis time to a practical interval, and helpminimize bleed at the higher temperatures
required to elute such compounds.
A comparative analysis of low boiling compounds on a 0.25µm, a 1.0µm, and a 5.0µm film of
stationary phase, with all other variables held constant, shows the influence of film thickness
(
Figure1
). The 0.25µm film does not resolve butanol from benzene (peaks 1 & 2). The 1.0µm
f
es about 80% resolution of this pair, but retention times aremore than double those
for the 0.25µm film. The 5.0µm film does not improve resolution between butanol and benzene,
relative to the 1.0µm film, and retention times are increased by a factor of six relative to the
0.25µm film. So, for this particular sample, the 1.0µm phase film is best: resolution is suitable
for quantifying the analytes, analysis time is acceptable, and a thicker film does not offer
notable improvements. On the other hand, if wewanted to resolve very volatile C2 or C3
