Unique Selectivity: The Power of Ionic Liquid GC Columns Leonard M. Sidisky, Jamie L. Desorcie, Gustavo Serrano Izaguirre, Daniel L. Shollenberger; Greg A. Baney, Katherine K. Stenerson, and Michael D. Buchanan Supelco, Div. of Sigma-Aldrich Bellefonte, PA 1823 USA T415083 sigma-aldrich.com/analytical
Abstract Choosing a stationary phase is the most critical step in column selection, more important than the column s I.D., film thickness, or length. This is because the stationary phase determines the selectivity of the column, and that selectivity influences resolution. Changing stationary phase may be an effective way to increase resolution. 1 Beginning in 200, extensive evaluations of columns manufactured with ionic liquid stationary phases have occurred. Their main strength was discovered to be unique selectivity. These columns have the ability to perform many of the same applications as columns made with polysiloxane polymer or polyethylene glycol stationary phases of similar polarity, but with slight elution order changes. Many times this results in increased resolution and/or shorter run times. 2
GC Column Polarity Scale A test was devised to experimentally determine which, if any, non-ionic liquid columns have similar polarity to each ionic liquid column. The procedure we adopted was proposed by Prof. Luigi Mondello (University of Messina, Italy). Each column was first characterized using a series of five probes (benzene, n-butanol, 2-pentanone, nitropropane, and pyridine). N-alkane markers were used to determine the retention index for each probe. McReynolds Constants were then calculated using the retention index data of each column relative to the retention index data for the same five probes on squalane, the most nonpolar GC stationary phase. The five McReynolds Constants were then summed to obtain Polarity (P) values, which were then normalized to SLB-IL100 (set at P.N. = 100) to obtain Polarity Number (P.N.) values. Figure 1 shows the tabulated results, whereas a visual representation is displayed in Figure 2. 3
Figure 1. Tabulated Results McReynolds Constants Column Benzene N-Butanol 2-Pentanone Nitropropane Pyridine P P.N. SPB -Octyl 17-20 19 28 1 Equity -1 11 10 33 0 1 130 3 SLB -5ms 33 30 55 91 43 252 SPB-20 7 79 104 17 109 535 12 Equity-1701 82 131 150 233 13 732 1 SPB-35 175 113 151 225 175 839 19 SPB-50 154 134 17 2 218 948 21 SPB-225 233 342 342 501 375 1793 40 PAG 27 459 320 508 428 1991 45 SUPELCOWAX 10 334 509 375 01 505 2324 52 SLB-IL59 338 505 549 49 583 224 59 SLB-IL0 32 492 525 7 54 222 59 SLB-IL1 371 551 51 24 48 2710 1 SP -2330 49 3 08 859 712 3311 75 SLB-IL7 45 90 43 845 745 3379 7 SP-2331 495 74 22 85 735 3382 7 SP-250 510 724 52 913 773 3572 81 SLB-IL82 532 7 701 921 808 338 82 TCEP 22 871 772 1072 957 4294 97 SLB-IL100 02 853 884 1017 1081 4437 100 SLB-IL111 7 930 957 1192 1093 4938 111 4
Figure 2. Visual Representation 5
Polarity and Selectivity A quick look at Figure 2 reveals the following regarding column polarity: SLB-IL59, SLB-IL0, and SLB-IL1 are somewhat similar in polarity (slightly more polar) to columns made with a polyethylene glycol (PEG) stationary phase. SLB-IL7 and SLB-IL82 are similar in polarity to columns made with a polysiloxane polymer stationary phase that contains a high percentage of cyanopropyl pendent groups. SLB-IL100 is very close in polarity to columns made with the TCEP stationary phase; TCEP = 1,2,3-tris(2-cyanoethoxy)propane. SLB-IL111 has a polarity unlike any other GC column. Polarity comparisons are a good start, but do not tell the whole story. Recent solvation parameter model (SPM) evaluations indicate that only the ionic liquid columns are capable of simultaneously providing intense H-acceptor and intense H-donor interactions, along with dipolar and - interactions. 2 These multiple interactions result in unique selectivity, and may produce better resolution and/or faster analysis.
Examples Several examples of unique selectivity resulting in better resolution and/or faster analysis are illustrated in Figure 3 through Figure 9. 7
Figure 3. Fusel Alcohols; 90 ºC Isothermal SLB-IL0 30 m x 0.25 mm I.D., 0.20 µm PEG 30 m x 0.25 mm I.D., 0.25 µm 2 1. 2-Methyl-1-Butanol (Active Amyl Alcohol) 2. 3-Methyl-1-Butanol (Isoamyl Alcohol) 1,2 1 0 2 4 Time (min) 1.0 2.0 3.0 4.0 5.0.0 Time (min) 8
Figure 4. Anilines; 75 ºC (2 min), 10 ºC/min to 250 ºC SLB-IL59 30 m x 0.25 mm I.D., 0.20 µm 3 4 1 5 7 1. Aniline 2. 3-(Chloromethyl)pyridine 3. 2-Aminotoluene 4. 4-Aminotoluene 5. 3-Aminotoluene. 2,-Dimethylaniline 7. 2,4-Dimethylaniline 2 11.0 12.0 13.0 PEG 30 m x 0.25 mm I.D., 0.25 µm 1 3 4 5 7 2 12.0 13.0 14.0 9
Figure 5. Aromatics in Reformulated Gasoline; Last Analyte to Elute is 1-Methylnaphthalene (1 mn) SLB-IL111 (1 mn elutes at 14.7 min) 0 m x 0.25 mm I.D., 0.20 µm B TCEP (1 mn elutes at 39.4 min) 0 m x 0.25 mm I.D., 0.44 µm 10
Figure. Esters and Ethers; 40 ºC (4 min), 8 ºC/min to 200 ºC (5 min) 1 1 2 3 2, 3 4 4 1 5 5 SLB-IL0 30 m x 0.25 mm I.D., 0.20 µm 7 PEG 30 m x 0.25 mm I.D., 0.25 µm 7 8 9 8 2 4 8 10 Time (min) 9 10 10 11 11 C 12 12 1. Methyl formate 2. Ethyl formate 3. Methyl acetate 4. Tetrahydrofuran 5. Ethyl acetate. Isopropyl acetate 7. n-propyl acetate 8. Isobutyl acetate 9. 1,4-Dioxane 10. n-butyl acetate 11. Isoamyl acetate 12. n-amyl acetate C. Contaminant 2 4 8 10 Time (min) 11
Figure 7. Polychlorinated Biphenyls (PCBs) SLB-IL82 30 m x 0.25 mm I.D., 0.20 µm; 50 ºC (2 min), 5 ºC/min to 20 ºC Poly(cyanopropylphenyl)siloxane 30 m x 0.25 mm I.D., 0.20 µm 0 ºC (1 min), 8 ºC/min to 230 ºC 12
2 1 3 4 Figure 8. Fatty Acid Methyl Esters (FAMEs); 170 ºC, 1 ºC/min to 225 ºC 5 7 SLB-IL0 30 m x 0.25 mm I.D., 0.20 µm 8 9 10 11 12 13 14 15 18 1 17 20 19 21 23 28 22 24 25 2 27 29 30 31 32 33 34 10 20 30 Min PEG 30 m x 0.25 mm I.D., 0.25 µm 18 1 17 20 19 21 37 35 3 3 min 38 1. C4:0 2. C:0 3. C8:0 4. C10:0 5. C11:0. C12:0 7. C13:0 8. C14:0 9. C14:1 10. C15:0 11. C15:1 12. C1:0 13. C1:1 14. C17:0 15. C17:1 1. C18:0 17. C18:1n9c 18. C18:1n9t 19. C18:2nc 20. C18:2nt 21. C18:3n 22. C18:3n3 23. C20:0 24. C20:1n9 25. C20:2 2. C20:3n 27. C21:0 28. C20:3n3 29. C20:4n 30. C20:5n3 31. C22:0 32. C22:1n9 33. C22:2 34. C23:0 35. C22:5n3 3. C24:0 37. C22:n3 38. C24:1n9 13
Figure 9. FAMEs in B20 Biodiesel; 50 ºC, 13 ºC/min to 270 ºC (5 min) SLB-IL111 30 m x 0.25 mm I.D., 0.20 µm No overlap of hydrocarbon and FAME fractions PEG 30 m x 0.25 mm I.D., 0.25 µm 14
Figure 10. Chlorinated Solvents; 40 ºC (4 min), 8 ºC/min to 200 ºC (5 min) 2 1 5 SLB-IL0 30 m x 0.25 mm I.D., 0.20 µm 4 3 1 5 4 9 7 10 8 11 2 4 8 10 11 12 Time (min) 2 3, 4 3 12 PEG 30 m x 0.25 mm I.D., 0.25 µm 14 1. 1,1-Dichloroethylene 2. trans-1,2-dichloroethylene 3. Carbon tetrachloride 4. 1,1,1-Trichloroethane 5. 1,1-Dichloroethane. Methylene chloride 7. Trichloroethylene 8. Tetrachloroethene 9. Chloroform 10. 1,2-Dichloroethane 11. 1,1,1,2-Tetrachloroethane 12. 1,1,2,2-Tetrachloroethane 5 7 10 8 11 12 9 2 4 8 10 12 Time (min) 14 1 15
Figure 11. Native Spearmint Essential Oil; 75 ºC (4 min), 4 ºC/min to 200 ºC (10 min) SLB-IL0 30 m x 0.25 mm I.D., 0.20 µm 0 10 20 30 40 Min PEG 30 m x 0.25 mm I.D., 0.25 µm 0 10 20 30 Min 1
Summary Ionic liquid stationary phases are something totally new and completely different in the world of GC. Because their wide range of interaction mechanisms translates to different selectivity options, they have the opportunity to positively impact current GC and GC-MS practices. Columns can be engineered with completely unique selectivity to non-ionic liquid columns, while producing good peak shape and resolution for compounds of varying functionality. Equity, SLB SP, SPB, and SUPELCOWAX is a registered trademarks of Sigma-Aldrich Co. LLC. 17
References 1. Barry E.F., Columns: packed and capillary; column selection in gas chromatography. In: Grob R.L., Barry E.F., editors. Modern Practice of Gas Chromatography, Fourth Edition. New Jersey: John Wiley & Sons, Inc.; 2004. p 5 191. 2. Rodríguez-Sánchez S., Galindo-Iranzo P., Soria A.C., Sanz M.L., Quintanilla-López J.E., Lebrón-Aguilar R., Principle component analysis (PCA) evaluation of seven commercial ionic liquid capillary GC columns. Supelco Reporter/2015; 33.1: 3-4. Equity, SLB, SP, SPB, and SUPELCOWAX are registered trademarks of Sigma-Aldrich Co. LLC. 18
Thank You 19