Supelco SLB-IL100 Ionic Liquid Capillary GC Column

By: Katherine K. Stenerson, katherine.stenerson@sial.com, Reporter US Volume 26.3

Polarity/Selectivity Benefits Without the Penalty of Low Maximum Temperature


Introduction

In our last Reporter (1), we introduced an exciting new phase technology using ionic liquids. Our first column in this line, the SLB-IL100, is similar in polarity to 1,2,3-tris(2- cyanoethoxypropane) (TCEP), one of the most polar stationary phases currently available. The benefits the SLB-IL100 offers is its significantly higher maximum temperature of 230 °C vs. 140 °C for the TCEP, and improved phase stability. These characteristics allow “TCEP-like” polarity to be utilized in applications requiring a column with a maximum temperature higher than 140 °C, while providing an alternative selectivity to currently available polar columns. In this article, we will compare the selectivity of the SLB-IL100 to “traditional” polar capillary GC columns for applications, fatty acid methyl esters (FAMEs), and PCB congeners.

back to top Back to Top

Fatty Acid Methyl Esters on the SLB-IL100 Column

TCEP is not typically used for the analysis of FAMEs due to its low temperature limit of 140 °C. There are a variety of columns less polar than TCEP available for the analysis of FAMEs, each with distinctive characteristics for this application. For example, the Omegawax™ is a polyethylene glycol (PEG) phase capillary column, which elutes FAMEs primarily by chain length and degree of unsaturation (Figure 1). However, this phase does not have the selectivity to resolve all groups of geometric isomers. For example, in Figure 1, C18:1n9 cis and trans coelute. For resolving geometric isomers, phases with higher polarity than PEG-based are used. The SLB-IL100 falls under this classification, and exhibits different selectivity towards FAMEs than the PEG-based Omegawax. The same FAME mixture shown on the Omegawax in Figure 1 was run under similar conditions on an SLB-IL100 column (Figure 2). The C18:1n9 geometric isomers were resolved, and differences in elution order were observed between the two columns, as noted in Table 1. Due to its higher polarity, retention was less on the SLBIL100 compared to the Omegawax, and elution of the saturated FAMEs was generally shifted further in ahead of the unsaturates. For example, C21:0 elutes prior to C20:2 and C20:3n6, and C22:0 elutes prior to C20:3n3 and C20:5n3 on the SLB-IL100, while on the Omegawax these saturates elute after.


Figure 1 37-Component FAME Mix on the Omegawax 250 (24136)(47885-U)

Figure 2 37-Component FAME Mix on the SLB-IL100 (28884-U)(47885-U)

Peak IDs for Methyl Esters in Figures 1 and 2

Table 1 Elution Order Differences of FAMEs on the Omegawax and the SLB-IL100

back to top Back to Top

PCB Congeners on the SLB-IL100

PCB congeners are hydrophobic, and when analyzed on a non-polar capillary column, such as a poly(5% diphenyl/ 95% dimethylsiloxane), retention increases with the degree of chlorination, with more overlap between the elution ranges as chlorination increases. The decachlorinated congener (decachlorobiphenyl), being the heaviest and most hydrophobic, elutes last. By contrast, on a highly polar column such as the SP-2331, the elution pattern is quite different. The analysis of a mixture of mono-chlorinated through deca-chlorinated congeners on the SP-2331 is presented in Figure 3. While dispersive interaction is the primary mechanism exhibited by nonpolar columns, separation using a polysiloxane phase with a high biscyanopropyl content, such as the SP-2331, will be governed by additional mechanisms such as strong dipole-induced dipole interactions. As a result, the deca-chlorinated congener is not as retained on this phase. The deca-chlorinated congener, #209, actually elutes prior to several other congeners. The same mixture on the SLB-IL100, under the same analysis conditions, is presented in Figure 4. Notice that, similar to the SP-2331, #209 elutes prior to several other congeners. However, the higher polarity of the SLB-IL100 has resulted in shorter elution time than the SP-2331 for all congeners. In addition to a shorter elution time, some elution order differences were observed between the two columns, as summarized in Table 2. The structure of PCB congeners suggests that they are capable of dipole and π interactions. While dipoleinduced dipole interactions are likely the predominant contributor to selectivity for the SP-2331, the ionic liquid used in the SLB-IL100 has the additional capability of interacting with the congeners’ π electrons, thus providing it with different selectivity than the SP-2331.

Figure 3 Mono- thru Deca-chlorobiphenyl PCB Congener Standard on the SP-2331 (24257)

Figure 4 Mono- thru Deca-chlorobiphenyl PCB Congener Standard on the SLB-IL100 (28884-U)

Peak IDs for Figures 3 and 4

Table 2 Elution Order Differences of PCB Congeners on SP-2331 and SLB-IL100

back to top Back to Top

SLB-IL100: A Superior Highly Polar Column

The SLB-IL100 shows promise as a superior highly polar column. Its higher maximum temperature and phase stability make it capable of analyzing higher molecular weight compounds than those possible with the highly polar TCEP phase. In comparison with other current polar and highly polar GC phases, such as PEG and biscyanopropylsiloxane, it offers alternative selectivity that can be utilized to “fine tune” specific separations. Future Reporter issues will highlight the applicability of the SLB-IL100 for additional uses.

back to top Back to Top

Outlook for Future Supelco Ionic Liquid GC Columns

The patented and successful use of ionic liquids as viable GC stationary phases heralds in a new and exiting chapter in GC phase technology. A full family of columns that utilize ionic liquid phase chemistry is planned. For example, an ionic liquid column with a polarity and selectivity similar to that of Carbowax® 20M, but with a maximum temperature over 300 °C, is just one of many possibilities currently being investigated. Look for additional Supelco ionic liquid GC columns to be introduced in the coming months. This is truly an exciting time in capillary GC column technology!

back to top Back to Top

Materials

     

References

  1. L.M. Sidisky and M.D. Buchanan, Supelco Patented Ionic Liquid GC Phase Technology, Supelco Reporter, April 2008; Vol. 26.2: 3-4.

back to top Back to Top

Related Links