36 May / June 2016
Better with Both: Leveraging Polar Selectivity and Polar Inertness using SLB®
by Leonard M. Sidisky, Gustavo Serrano, James L. Desorcie, Greg Baney, and Michael D. Buchanan MilliporeSigma, 595 N. Harrison Road, Bellefonte, PA 16823, USA A business of Merck KGaA, Darmstadt, Germany
len.sidisky@
sial.com
Improved column inertness for polar analytes was the inspiration for the development of SLB-IL (i-series) ionic liquid capillary GC columns. They solve a dilemma that has existed for a long time; when analysing compounds with polar functionality, is it better to optimise for polar selectivity or polar inertness? With i-series columns, GC users can benefit from improved polar selectivity and polar inertness! Figure 1 illustrates the resulting benefits.
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 specification for all three chemistries, whereas Figure 2 shows the structure of each stationary phase.
Improved Inertness
To demonstrate improved inertness, a polar column test mix containing four polar analytes and five n-alkane markers was analysed on two columns; SLB-IL76i (the improved inertness version) and SLB-IL76 (the original version). Both chromatograms are displayed in Figure 3. 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.
Active Amyl Alcohol
and Isoamyl Alcohol
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 analysed on each i-series column. The chromatograms shown in Figure 4 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
Table 1. Column Specifications
-IL (i-series) Capillary GC Columns
chemistries. In fact, the alcohol peak shapes compare favourably to the n-alkane peak shapes! The inclusion of n-alkane markers allows some of the selectivity characteristic of each column to be revealed. These figures demonstrate the difference in selectivity between the three columns with the polar
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