Supelco SLB-IL60 Ionic Liquid GC Columns: Unique Selectivity

By: Leonard M. Sidisky, Katherine K. Stenerson, Michael D. Buchanan, Reporter US Volume 32.2

The SLB®-IL60 gas chromatography (GC) column is based on the ionic liquid stationary phase platform, and displays desirable features that existing non-ionic liquid columns do not. This is the first of several Reporter articles which explore various aspects of this column. The SLB-IL60 column is able to undergo the same analyte-phase interactions as polyethylene glycol (PEG) columns, but at different relative amounts. Based on its unique phase structure, the SLB-IL60 column is also able to undergo additional interactions that PEG columns cannot.

  • With PEG columns, possible interactions appear to be dispersive, hydrogen bonding, and acid-base
  • With SLB-IL60 columns, possible interactions appear to be dispersive, dipole-dipole, dipole-induced dipole, π-π hydrogen bonding, and acid-base

As such, the SLB-IL60 column will retain some polar and polarizable analytes relatively longer, and some non-polar analytes relatively less. This results in unique and alternate selectivity compared to PEG columns.

The SLB-IL60 column was compared directly to five popular commercially available PEG columns, each from a different manufacturer. The dimensions for the columns were 30 m x 0.25 mm I.D., 0.25 µm, except the SLB-IL60 column, which has a 0.20 µm film thickness. Table 1 shows the maximum temperature limits for all columns tested. Complete specifications of SLB-IL60 columns are shown in Table 2.

Table 1. Maximum Temperature Limits*
Column
Isothermal °C
Programmed °C
PEG 1
280
280
PEG 2
260
270
PEG 3
250
260
PEG 4
250
260
PEG 5
280
300
SLB-IL60
300
300
* Obtained from paperwork included with commercial columns.

 

Table 2. SLB-IL60 Column Specifications
Application Modified (deactivated) version of SLB-IL59 provides better inertness. Selectivity more polar than PEG/wax phases, resulting in unique elution patterns. Higher maximum temperature than PEG/wax columns (300 °C compared to 270-280 °C). Excellent alternative to existing PEG/wax columns. Also a good GCxGC column choice.
USP Code None
Phase Non-bonded; 1,12-Di(tripropylphosphonium)dodecane bis(trifluoromethylsulfonyl)imide
Temp. Limits 35 °C to 300 °C (isothermal or programmed)


Esters and Ethers

A 12-component esters and ethers mix was analyzed on each column under identical conditions. All five PEG columns produced almost identical chromatography. Figure 1 shows chromatograms obtained from the PEG 1 and SLB-IL60 columns. Observations are that the SLB-IL60 column provides:

  • Resolution of ethyl formate (peak 2) and methyl acetate (peak 3)
  • Longer relative retention of isopropyl acetate (peak 6)
  • Longer relative retention of isobutyl acetate (peak 8) and shorter relative retention of 1,4-dioxane (peak 9), resulting in an elution order change
  • Resolution of a contaminant peak (peak c), suspected to be 2-methylbutyl acetate, from isoamyl acetate (peak 11)

Figure 1: Esters and Ethers

CONDITIONS: columns: PEG 1, 30 m x 0.25 mm I.D., 0.25 µm df; SLB-IL60, 30 m x 0.25 mm I.D., 0.20 µm df (29505-U); oven: 40 °C (4 min), 8 °C/min to 200 °C (5 min); inj. temp.: 250 °C; carrier gas: helium, 30 cm/sec; detector: FID, 250 °C; injection: 1 µL, 100:1 split; liner: 4 mm I.D., split/splitless type, single taper wool packed, FocusLiner design; sample: 12-component esters and ethers mix, each analyte at 0.2 % (v/v) in pentane


Chlorinated Hydrocarbons

A 12-component chlorinated hydrocarbon mix was analyzed on each column under identical conditions. All five PEG columns produced very similar chromatography, with the PEG 2 column producing the best overall resolution. Several PEG columns were unable to provide resolution of tetrachloroethene (peak 8) and chloroform (peak 9). Figure 2 shows chromatograms obtained from the PEG 2 and SLB-IL60 columns. Observations are that the SLB-IL60 column provides:

  • Significantly less retention (11 minutes compared to 16 minutes)
  • Many elution order differences (peaks 3-10)
  • Resolution of carbon tetrachloride (peak 3) and 1,1,1-trichloroethane (peak 4)

Figure 2: Chlorinated Solvents

CONDITIONS: columns: PEG 2, 30 m x 0.25 mm I.D., 0.25 µm df, SLB-IL60, 30 m x 0.25 mm I.D., 0.20 µm df (29505-U); oven: 40 °C (4 min), 8 °C/min to 200 °C (5 min); inj. temp.: 250 °C; carrier gas: helium, 30 cm/sec; detector: FID, 250 °C; injection: 1 µL, 100:1 split; liner: 4 mm I.D., split/splitless type, single taper wool packed, FocusLiner™ design; sample: 12-component chlorinated solvent mix, each analyte at 0.2 % (v/v) in pentane


Fatty Acid Methyl Esters (FAMEs)

A 38-component FAME mix was analyzed on each column under identical conditions. All five PEG columns produced very similar chromatography, with the PEG 3 column producing the best overall resolution. Figure 3 shows chromatograms obtained from the PEG 3 and SLB-IL60 columns. Observations are that the SLB-IL60 column provides:

  • An overall faster elution (36 minutes compared to 52 minutes)
  • Resolution of C18:1n9c (peak 17) and C18:1n9t (peak 18)
  • Elution of trans isomers (peaks 18 and 20) before cis isomers (peaks 17 and 19)
  • Less relative retention of C20:3n3 (peak 28) resulting in an elution order change
  • Elution of C22:6n3 (peak 37) before C22:5n3 (peak 35)

Figure 3: FAMEs

CONDITIONS: columns: PEG 3, 30 m x 0.25 mm I.D., 0.25 µm df, SLB-IL60, 30 m x 0.25 mm I.D., 0.20 µm df (29505-U); oven: 170 °C, 1 °C/min to 225 °C; inj. temp.: 250 °C; carrier gas: helium, 1.2 mL/min; det.: FID, 260 °C; injection: 1 µL, 100:1 split; liner: 4 mm I.D., split/splitless type, single taper wool packed FocusLiner design; sample: Supelco 37-Component FAME Mix (CRM47885) + C22:5n3, in methylene chloride


Conclusion

Columns based on polyethylene glycol phase chemistry are widely used for a variety of applications (such as solvents and FAMEs). However, modification of PEG phase chemistry to affect selectivity is very limited. The SLB-IL60 column is able to undergo many of the same analyte-phase interactions as PEG columns, plus some additional interactions. This results in the SLB-IL60 column being similar enough to PEG columns to make it useful for many of the same applications, but different enough to impart unique selectivity which can be leveraged to change elution patterns and/or improve resolution.

Featured Products
Description Cat. No.
SLB-IL60 GC Columns
15 m x 0.10 mm I.D., 0.08 µm df 29503-U
20 m x 0.18 mm I.D., 0.14 µm df 29504-U
30 m x 0.25 mm I.D., 0.20 µm df 29505-U
60 m x 0.25 mm I.D., 0.20 µm df 29506-U
30 m x 0.32 mm I.D., 0.26 µm df 29508-U
60 m x 0.32 mm I.D., 0.26 µm df 29509-U
Analytical Standard
37 Component FAME mix CRM47885

Trademarks

  • SLB is a registered trademark of Sigma-Aldrich Co. LLC
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