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• Higher peak capacity.
• Signal enhancement due to analyte refocusing in the thermal
modulator.
• Ability to record a series of 2-D chromatograms (i.e., retention time
versus signal) that can be transformed into a three-dimensional
chromatogram (Figure 7.10).
In forensic analysis, the approach has been applied to differentiate
between different ignitable liquids in fire debris samples.
1
It has also been
used in food and fragrance analyses.
7.3.3 Ionic Liquid GC Columns
The types of 'traditional' stationary phases used in GC have been discussed
previously (see Section 2.5). A distinctly different type of stationary phase
has emerged within the last decade based on ionic liquids. An ionic liquid
is characterised as a solvent with both organic cations associated with either
inorganic or organic anions and an inherently low melting point. The key
properties that make ionic liquids suitable as stationary phase for GC include:
• Low volatility (i.e., potential for the column to have a longer opera-
tional lifetime).
• Good temperature stability (i.e., potential for the column to remain
in the liquid state over an extended temperature range).
• No reactive hydroxyl groups (i.e., potential for the column to be
resistant to damage from water and oxygen).
• Highly polar (i.e., potential for the column to have a high polarity).
• Range of physical—chemical solvation characteristics (i.e., potential
for the column to have unique selectivity).
A typical ionic liquid stationary phase (e.g., SLB-IL 100, from Supelco) is
shown in Figure 7.11.
anion
anion
CF
3
CF
3
linkage
cation
cation
O
O
S
S
N
N
O
O
N
N
+
+
N
-
N
-
O
O
S
S
O
O
CF
3
CF
3
Figure 7.11
Ionic liquid phase. (Source: Supelco ionic liquid GC columns,
Sigma-Aldrich, 22 January 2011. With permission.)
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