32 May / June 2014
greater than 90% cyanopropyl substitution in the polymer backbone.
Thermal Stability
Higher temperature GC columns are desirable, as they may allow decreased analysis times, elevated bake-out to remove large non-target compounds, and analysis of higher boiling compounds. However, higher oven temperatures also tend to accelerate the amount of column bleed. When working with a flame ionisation detector (FID), excessive bleed is undesirable as it lowers the signal-to-noise, resulting in a loss of sensitivity. Column manufacturers routinely list the maximum temperature a column can safely be used at before the level of column bleed renders the column unusable.
Figure 5: FAME Selectivity Comparison of SLB-IL60 and Omegawax 250 Conditions
Omegawax 250: 30 m x 0.25 mm I.D., 0.25 µm
SLB-IL60 column: SLB-IL60, 30 m x 0.25 mm I.D., 0.20 µm (29505-U) oven: SLB-IL60- 180°C isothermal Omegawax 250- 190°C isothermal
inj. temp.: 250°C
carrier gas: helium, 1 mL/min detector: FID, 250°C injection: 1 µL, split 100:1
the FAME compounds some unique shifting in the elution pattterns are demonstrated. Specifically, the SLB-IL60 column elutes the C22:6n3 FAME prior to the C22:5n3 FAME while the Omegawax 250 provides the typical PEG elution pattern of these two compounds.
Another application that demonstrates differences in selectivity of the SLB-IL60 and a traditonal PEG column is the analysis of cis and trans fatty acid methyl esters (FAMEs). Traditional PEG phases typically elute the cis isomers as a group prior to the trans isomers group with little to no separation of the geometric isomers of the same degree of
unsaturation (monoene, diene, triene, etc>). Figure 6 demonstrates the separation of C18:1 and C18:2 cis and trans FAMEs on both the SLB-IL60 and the traditional PEG column.
Traditional polyethylene glycol phases (PEG) are known to provide cis & trans isomer separation with the cis isomer eluting prior to the trans isomer. The SLB-IL60 ionic liquid column (with a PEG like polarity) offers a unique selectivity for cis and trans isomer separations as the trans isomer elutes prior to the cis isomers. The elution of the trans isomer prior to the cis isomer is similar to the selectivity of the more highly polar cyanosilicone phases containing
To illustrate the lower FID bleed characteristic of the SLB-IL60 column, it was compared directly to five popular commercially available PEG columns, each from a different manufacturer. All columns were 30 m x 0.25 mm I.D., 0.25 µm dimensions, except the SLB-IL60 column, which has a 0.20 µm film thickness. The slightly lower film thickness for the SLB-IL60 column contributes to a slightly lower bleed than the 0.25 µm films for the PEG columns but it is not the major factor for the lower bleed.
Table 1 shows the maximum temperature limits for all columns tested.
Table 1. Maximum Temperature Limits* Column Isothermal Programmed PEG 1
PEG 2 PEG 3 PEG 4 PEG 5
SLB-IL60
280°C 260°C 250°C 250°C 280°C 300°C
280°C 270°C 260°C 260°C 300°C 300°C
* Obtained from paperwork included with commercial columns.
Figure 6a: C18:1n9 cis & trans FAMEs @ 180°C
Figure 6b: C18:2n6 cis & trans FAMEs @ 180°C
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