6 Gas Chromatography Columns Using Ionic Liquids …
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(5%-diphenyl/95%-dimethyl polysiloxane, 50%-diphenyl/50%-dimethyl polysiloxane, 14%-cyanopropyl/86%-polydimethylsiloxane, etc.). However, none of these
polysiloxane-based columns provide broad selectivities for the separation of isomers
within a homologous series [122]. Polysiloxane-based columns showed 38–56%
coelution during analyses of 119 PASHs [123]. However, the IL-based GC stationary phases performed better with 32–38% coelutions, and the SLB-IL111 column
was the best with 32% coelutions [123]. Separation and determination of ratios of
some target PASHs is important in environmental forensic studies to determine the
source and the extent of fossil fuel weathering. For example, ratios of 1-, 2-, 3-, and
4-methyldibenzothiophene (MeDBT) vary with petroleum source. 2- and 3-MeDBT
coelute on the polysiloxane-based stationary phases, while they can be baseline separated on the SLB-IL111 column [123]. IL columns also have advantages in the
separation of isomeric pairs of 1,3,7- and 3,4,7-trimethyldibenzothiophene, 6- and
8-methylbenzo[b]naphthol[1,2-d]thiophene, 2- and 9-methylbenzo[b]naphthol[1,2d]thiophene, and 4- and 7-methylbenzo[b]naphthol[2,1-d]thiophene compared to
siloxane columns [123].
The retention behavior of the PASHs is determined by the polarity and polarizability of the analytes [123]. Polarizability is mainly dependent on the molecular geometry. Linear PASHs (e.g., anthracene analogs) are more polarizable than condensed
PASHs (e.g., pyrene analogs) with the same number of rings [123]. The polarity is
dependent on the position of the sulfur atom. For example, PASHs with “protected”
sulfur in a bay-region (benzo[b]naphthol[2,1-d]thiophene) or by an alkyl group on
the adjacent carbon (6-methylbenzo[b]naphthol[1,2-d]thiophene) are less polar compared to PASHs with an exposed sulfur (benzo[b]naphthol[1,2-d]thiophene) [123].
PASHs with higher polarizability and polarity showed higher retention with respect to
low polarizable and polar PASHs on all the columns. The relatively more polar PASHs
(exposed sulfur) showed higher retention on the IL column compared to polysiloxane
columns [123]. The IL column SLB-IL60 showed increased separation space and
resolution for the separation of PASHs in the GC × GC applications compared to the
polysiloxane columns. In GC × GC applications, IL columns provided increased separation of more polarizable PASHs compared to the polydimethylsiloxane columns
[123].
Polycyclic aromatic hydrocarbons (PAHs) are common environmental pollutants
derived from incomplete combustion of organic material. PAHs are toxic pollutants,
and they have mutagenic and carcinogenic activities. Most of the PAHs are structural
isomers, and their chromatographic separation is important for the quantitation of
individual isomers. A specially developed IL column SLB-ILPAH was recently introduced for the effective separation of 22 PAHs. The SLB-ILPAH column consists of
1,12-di(tripropylphosphonium) dodecane bis(trifluoromethanesulfonyl)imide IL as
a stationary phase and the column dimensions are 20 m × 0.18 mm i.d., 0.05 μm d f .
Structural isomers of “benzo-fluoranthene” and “dibenzo-pyrene” are difficult to separate on the other GC stationary phases but can be easily and rapidly separated using
a SLB-ILPAH column. When a non-commercialized IL [2mC 3 (mim) 2 ][CTf 3 ] 2 containing tris(trifluoromethanesulfonyl)methide [CTf 3 ]
– anion was used during PAH
analysis, an unusual selectivity in the separation of anthracene and phenanthrene was
151
(5%-diphenyl/95%-dimethyl polysiloxane, 50%-diphenyl/50%-dimethyl polysiloxane, 14%-cyanopropyl/86%-polydimethylsiloxane, etc.). However, none of these
polysiloxane-based columns provide broad selectivities for the separation of isomers
within a homologous series [122]. Polysiloxane-based columns showed 38–56%
coelution during analyses of 119 PASHs [123]. However, the IL-based GC stationary phases performed better with 32–38% coelutions, and the SLB-IL111 column
was the best with 32% coelutions [123]. Separation and determination of ratios of
some target PASHs is important in environmental forensic studies to determine the
source and the extent of fossil fuel weathering. For example, ratios of 1-, 2-, 3-, and
4-methyldibenzothiophene (MeDBT) vary with petroleum source. 2- and 3-MeDBT
coelute on the polysiloxane-based stationary phases, while they can be baseline separated on the SLB-IL111 column [123]. IL columns also have advantages in the
separation of isomeric pairs of 1,3,7- and 3,4,7-trimethyldibenzothiophene, 6- and
8-methylbenzo[b]naphthol[1,2-d]thiophene, 2- and 9-methylbenzo[b]naphthol[1,2d]thiophene, and 4- and 7-methylbenzo[b]naphthol[2,1-d]thiophene compared to
siloxane columns [123].
The retention behavior of the PASHs is determined by the polarity and polarizability of the analytes [123]. Polarizability is mainly dependent on the molecular geometry. Linear PASHs (e.g., anthracene analogs) are more polarizable than condensed
PASHs (e.g., pyrene analogs) with the same number of rings [123]. The polarity is
dependent on the position of the sulfur atom. For example, PASHs with “protected”
sulfur in a bay-region (benzo[b]naphthol[2,1-d]thiophene) or by an alkyl group on
the adjacent carbon (6-methylbenzo[b]naphthol[1,2-d]thiophene) are less polar compared to PASHs with an exposed sulfur (benzo[b]naphthol[1,2-d]thiophene) [123].
PASHs with higher polarizability and polarity showed higher retention with respect to
low polarizable and polar PASHs on all the columns. The relatively more polar PASHs
(exposed sulfur) showed higher retention on the IL column compared to polysiloxane
columns [123]. The IL column SLB-IL60 showed increased separation space and
resolution for the separation of PASHs in the GC × GC applications compared to the
polysiloxane columns. In GC × GC applications, IL columns provided increased separation of more polarizable PASHs compared to the polydimethylsiloxane columns
[123].
Polycyclic aromatic hydrocarbons (PAHs) are common environmental pollutants
derived from incomplete combustion of organic material. PAHs are toxic pollutants,
and they have mutagenic and carcinogenic activities. Most of the PAHs are structural
isomers, and their chromatographic separation is important for the quantitation of
individual isomers. A specially developed IL column SLB-ILPAH was recently introduced for the effective separation of 22 PAHs. The SLB-ILPAH column consists of
1,12-di(tripropylphosphonium) dodecane bis(trifluoromethanesulfonyl)imide IL as
a stationary phase and the column dimensions are 20 m × 0.18 mm i.d., 0.05 μm d f .
Structural isomers of “benzo-fluoranthene” and “dibenzo-pyrene” are difficult to separate on the other GC stationary phases but can be easily and rapidly separated using
a SLB-ILPAH column. When a non-commercialized IL [2mC 3 (mim) 2 ][CTf 3 ] 2 containing tris(trifluoromethanesulfonyl)methide [CTf 3 ]
– anion was used during PAH
analysis, an unusual selectivity in the separation of anthracene and phenanthrene was