SLB®-IL (i-series) Capillary GC Columns: Enjoy Polar Selectivity and Polar Inertness

By: Leonard M. Sidisky, Michael D. Buchanan, and Gustavo Serrano, Reporter US Volume 34.3

For the analysis of polar analytes, is it better to optimize column selection for polar selectivity or polar inertness? This dilemma is now solved. Using SLB-IL (i-series) columns, GC users can enjoy both selectivity and inertness! With these columns, peak shapes for polar analytes, such as alcohols, ketones, anilines, and phenols, look as sharp as those observed with non-polar analytes, such as n-alkanes.

Better with Both

By providing both selectivity and inertness towards polar analytes, better accuracy and sensitivity can be achieved. An illustration comparing the chromatography of two analytes with similar boiling points on three column types is presented in Figure 1. Observations are:

  • SLB-IL (i-series) columns combine high selectivity for polar analytes and high inertness towards polar analytes, so provide resolution and good peak shapes for both analytes
  • Traditional highly polar columns, with high selectivity for polar analytes and low inertness towards polar analytes, provide resolution, but a poor peak shape for the polar analyte
  • Traditional non-polar columns have low selectivity for polar analytes and high inertness towards polar analytes, so provide good peak shapes for both analytes, but limited resolution


Comparison of Column Types

Figure 1. Comparison of Column Types

Improved Inertness

To demonstrate improved inertness, a polar column test mix containing four polar analytes and five n-alkane markers was analyzed on two columns; SLB-IL76i (the improved inertness version) and SLB-IL76 (the original version). Both chromatograms are displayed in Figure 2. Using the polar column test mix for the quality control of polar and highly polar columns allows an assessment of inertness. In particular:

  • The peak shapes of an alcohol, a ketone, a phenol (an aromatic alcohol), and an aniline (an aromatic amine) can be monitored – sharper peak shapes indicate a more inert column
  • The % response of 1-octanol (its peak height relative to a curved line connecting the n-alkane markers) can be measured – a greater value indicates a more inert column

As shown, SLB-IL76i exhibits improved inertness, established by the sharp peak shapes produced for all analytes with polar functionality. This is further demonstrated by the greater peak height of 1-octanol.

Inertness Comparison

Figure 2. Inertness Comparison

Selectivity Options

It is advantageous to have columns with alternative selectivity at hand, because resolution is most greatly affected by selectivity. A range of i-series columns were developed, classified as polar (SLB-IL60i), highly polar (SLB-IL76i), and extremely polar (SLB-IL111i). Table 1 contains complete specifications for each chemistry.


Table 1.
SLB-IL (i-series) Column Specifications

SLB®-IL60i

Application: The selectivity of SLB-IL60i is more polar than PEG/wax phases, resulting in unique elution patterns. It has a higher maximum temperature than most PEG/wax columns (280 °C compared to 260-270 °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(trifluoromethanesulfonyl)imide Temp.
Limits: 35 °C to 280 °C (isothermal or programmed)
SLB®-IL76i

Application:
The SLB-IL76i phase structure is engineered with numerous interaction mechanisms, resulting in selectivity differences even when compared to columns with similar GC column polarity scale values. Also a good GCxGC column choice.
USP Code: None
Phase: Non-bonded; Tri(tripropylphosphoniumhexanamido)triethylamine bis(trifluoromethanesulfonyl)imide Temp. Limits: subambient to 270 °C (isothermal or programmed)
SLB®-IL111i

Application: The selectivity of SLB-IL111i is most orthogonal to non-polar and intermediate polar phases, resulting in very unique elution patterns. Maximum temperature of 270 °C is very impressive for such an extremely polar column. Great choice for separation of polarizable analytes (contain double and/or triple C-C bonds) from neutral analytes. Also a good GCxGC column choice.
USP Code: None
Phase: Non-bonded; 1,5-Di(2,3-dimethylimidazolium)pentane bis(trifluoromethanesulfonyl)imide
Temp. Limits: 50 °C to 260 °C (isothermal or programmed)
 

 

Two by-products of the fermentation process are active amyl alcohol and isoamyl alcohol. Alcoholic beverage manufacturers are interested in these analytes due to their contribution to the aroma characteristic. A mix containing both analytes and several n-alkane markers was analyzed on each i-series column. The inclusion of n-alkane markers allows some of the selectivity characteristic of each column to be revealed.

The chromatograms shown in Figure 3 reveal that all three chemistries are able to perform this separation using a 90 °C isothermal oven temperature. Most other GC columns cannot perform this separation without resorting to lower (even sub-ambient) oven temperatures. Excellent peak shapes were exhibited for both analytes on all three chemistries. In fact, the alcohol peak shapes compare favorably to the n-alkane peak shapes!

These chromatograms also demonstrate the difference in selectivity between the three columns. In addition to being fully resolved, both alcohols elute between:

  • n-undecane and n-dodecane on the polar SLB-IL60i column
  • n-tridecane and n-tetradecane on the highly polar SLB-IL76i column
  • n-pentadecane and n-hexadecane on the extremely polar SLB-IL111i column

Selectivity Comparison

Figure 3. Selectivity Comparison

Conclusion

Improved inertness for polar analytes was the inspiration for the development of this new line of ionic liquid capillary GC columns. They provide both selectivity and inertness towards polar analytes, resulting in better accuracy and sensitivity. Having a range of selectivity options will provide analysts the capability to tailor their analyses.

Materials

     

 Reference

  1. Sidisky, L.M.; Serrano, G.; Desorcie, J.L.; Baney, G.; and Buchanan, M.D. Better with both: leveraging polar selectivity and polar inertness using SLB®-IL (i-series) capillary GC columns, Chrom. Today, 2016, 9.2, 36.

 

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