6 Gas Chromatography Columns Using Ionic Liquids …
145
been successfully used for separation of extracted fats from marine products. Using
this IL column along with time-of-flight (TOF) mass spectrometry, the separation
and accurate identification of 125 fatty acids in menhaden oil, including two novel
branched fats having a trans configuration, namely 7-methyl-6-hexadecenoic and
7-methyl-6-octadecenoic fatty acids, were achieved. The presence of small amounts
of t6-17:1 and t8-18:1 suggested that t6-18:1 may be chain-elongated in fish [59]. In
addition, analysis of fatty acids in marine oil omega-3 supplements on a 200 m SLBIL111 column permitted quantification of rarely reported fatty acids, such as C21:5n3
and the n-4 and n-1 polyunsaturated fatty acid (PUFA). The presence of predominant
mono-trans isomers of eicosapentaenoic acid (EPA; C20:5n3) and docosahexaenoic
acid (DHA; C22:6n3) was confirmed in these samples [90]. The SLB-IL100 was
tested for analysis of cis positional isomers of eicosenoic (C20:1) and docosenoic
(C22:1) fatty acids of fish origin. The high polarity of SLB-IL100 allowed separation
of several isomers including C20:1n11 from C20:1n13, which are unresolvable on
conventional polar polymer phase columns [91].
Steryl esters are a minor lipid class in animal and plant lipids with high molecular
mass (600–700 g/mol) that are usually analyzed by reverse-phase high-performance
liquid chromatography (RP-HPLC) [92–94]. However, several coelutions may occur
between steryl esters using C18 or hexyl-phenyl-modified HPLC stationary phases.
Also, high elution temperatures required for gas chromatographic analysis of these
compounds raise challenges to separate fatty acids present in the sterol backbones
efficiently [95]. A 12 m SLB-IL59 column was employed to separate fatty acid esters
of cholesterol and phytosterols. The high temperature limit (300 °C) and medium
polarity of SLB-IL59 allow separation of steryl esters both by total carbon number
and by the degree of unsaturation [92].
Application of the recently developed vacuum ultraviolet (VUV) detector along
with a SLB-IL111 column offers additional selectivity in the characterization of fats
and edible oils [76, 96]. The gas-phase VUV absorption spectra are significantly
selective to the molecular structure of analytes. VUV provides completely different
absorption profiles for unsaturated and saturated FAMEs. In addition, cis and trans
isomers can be easily distinguished in VUV due to their distinct spectra.
6.3.5 Multidimensional GC Separations
Ionic liquid columns have been used both in the first and second dimension of twodimensional gas chromatography (GC × GC) to enhance the separation of FAMEs
in complex matrices [58, 64, 69, 70, 97–103]. The major advantage of using GC ×
GC with IL columns is to obtain higher peak capacity, hence enhancing the resolution
between positional FAME isomers. The arrangement of highly polar SLB-IL100 in
the first dimension along with an intermediate polar column in the second dimension resulted in the effective separation of C18:1 isomers [103]. The SLB-IL82 and
SLB-IL100 were evaluated for one-dimensional and two-dimensional GC analyses of
fatty acids in marine biota [99]. Conventional GC analysis showed that these columns
145
been successfully used for separation of extracted fats from marine products. Using
this IL column along with time-of-flight (TOF) mass spectrometry, the separation
and accurate identification of 125 fatty acids in menhaden oil, including two novel
branched fats having a trans configuration, namely 7-methyl-6-hexadecenoic and
7-methyl-6-octadecenoic fatty acids, were achieved. The presence of small amounts
of t6-17:1 and t8-18:1 suggested that t6-18:1 may be chain-elongated in fish [59]. In
addition, analysis of fatty acids in marine oil omega-3 supplements on a 200 m SLBIL111 column permitted quantification of rarely reported fatty acids, such as C21:5n3
and the n-4 and n-1 polyunsaturated fatty acid (PUFA). The presence of predominant
mono-trans isomers of eicosapentaenoic acid (EPA; C20:5n3) and docosahexaenoic
acid (DHA; C22:6n3) was confirmed in these samples [90]. The SLB-IL100 was
tested for analysis of cis positional isomers of eicosenoic (C20:1) and docosenoic
(C22:1) fatty acids of fish origin. The high polarity of SLB-IL100 allowed separation
of several isomers including C20:1n11 from C20:1n13, which are unresolvable on
conventional polar polymer phase columns [91].
Steryl esters are a minor lipid class in animal and plant lipids with high molecular
mass (600–700 g/mol) that are usually analyzed by reverse-phase high-performance
liquid chromatography (RP-HPLC) [92–94]. However, several coelutions may occur
between steryl esters using C18 or hexyl-phenyl-modified HPLC stationary phases.
Also, high elution temperatures required for gas chromatographic analysis of these
compounds raise challenges to separate fatty acids present in the sterol backbones
efficiently [95]. A 12 m SLB-IL59 column was employed to separate fatty acid esters
of cholesterol and phytosterols. The high temperature limit (300 °C) and medium
polarity of SLB-IL59 allow separation of steryl esters both by total carbon number
and by the degree of unsaturation [92].
Application of the recently developed vacuum ultraviolet (VUV) detector along
with a SLB-IL111 column offers additional selectivity in the characterization of fats
and edible oils [76, 96]. The gas-phase VUV absorption spectra are significantly
selective to the molecular structure of analytes. VUV provides completely different
absorption profiles for unsaturated and saturated FAMEs. In addition, cis and trans
isomers can be easily distinguished in VUV due to their distinct spectra.
6.3.5 Multidimensional GC Separations
Ionic liquid columns have been used both in the first and second dimension of twodimensional gas chromatography (GC × GC) to enhance the separation of FAMEs
in complex matrices [58, 64, 69, 70, 97–103]. The major advantage of using GC ×
GC with IL columns is to obtain higher peak capacity, hence enhancing the resolution
between positional FAME isomers. The arrangement of highly polar SLB-IL100 in
the first dimension along with an intermediate polar column in the second dimension resulted in the effective separation of C18:1 isomers [103]. The SLB-IL82 and
SLB-IL100 were evaluated for one-dimensional and two-dimensional GC analyses of
fatty acids in marine biota [99]. Conventional GC analysis showed that these columns