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Unique Selectivity:The Power of Ionic Liquid GC ColumnsLeonard M. Sidisky, Jamie L. Desorcie, Gustavo Serrano Izaguirre,Daniel L. Shollenberger; Greg A. Baney, Katherine K. Stenerson,and Michael D. BuchananSupelco, Div. of Sigma-Aldrich Bellefonte, PA 16823 USA

T415083

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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 2006, 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.

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Abstract

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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 non-polar 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.

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Figure 1. Tabulated Results

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McReynolds ConstantsColumn Benzene N-Butanol 2-Pentanone Nitropropane Pyridine P P.N.SPB®-Octyl 17 -20 6 19 6 28 1

Equity®-1 11 10 33 60 16 130 3

SLB®-5ms 33 30 55 91 43 252 6

SPB-20 76 79 104 167 109 535 12

Equity-1701 82 131 150 233 136 732 16

SPB-35 175 113 151 225 175 839 19

SPB-50 154 134 176 266 218 948 21

SPB-225 233 342 342 501 375 1793 40

PAG 276 459 320 508 428 1991 45

SUPELCOWAX® 10 334 509 375 601 505 2324 52

SLB-IL59 338 505 549 649 583 2624 59

SLB-IL60 362 492 525 676 564 2622 59

SLB-IL61 371 551 516 624 648 2710 61

SP®-2330 469 663 608 859 712 3311 75

SLB-IL76 456 690 643 845 745 3379 76

SP-2331 495 674 622 856 735 3382 76

SP-2560 510 724 652 913 773 3572 81

SLB-IL82 532 676 701 921 808 3638 82

TCEP 622 871 772 1072 957 4294 97

SLB-IL100 602 853 884 1017 1081 4437 100

SLB-IL111 766 930 957 1192 1093 4938 111

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Figure 2. Visual Representation

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Polarity and Selectivity

A quick look at Figure 2 reveals the following regarding column polarity:• SLB-IL59, SLB-IL60, and SLB-IL61 are somewhat similar in polarity (slightly

more polar) to columns made with a polyethylene glycol (PEG) stationary phase.

• SLB-IL76 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 andintense 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.

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Examples

Several examples of unique selectivity resulting in better resolution and/or faster analysis are illustrated in Figure 3 through Figure 9.

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Figure 3. Fusel Alcohols; 90 ºC Isothermal

0 2 4 6Time (min)

1.0 2.0 3.0 4.0 5.0 6.0Time (min)

SLB-IL6030 m x 0.25 mm I.D., 0.20 µm

PEG30 m x 0.25 mm I.D., 0.25 µm

1

21,2

1. 2-Methyl-1-Butanol(Active Amyl Alcohol)

2. 3-Methyl-1-Butanol(Isoamyl Alcohol)

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Figure 4. Anilines; 75 ºC (2 min), 10 ºC/min to 250 ºC

11.0 12.0 13.0

12.0 13.0 14.0

1. Aniline2. 3-(Chloromethyl)pyridine3. 2-Aminotoluene4. 4-Aminotoluene5. 3-Aminotoluene6. 2,6-Dimethylaniline7. 2,4-Dimethylaniline

SLB-IL5930 m x 0.25 mm I.D., 0.20 µm

PEG30 m x 0.25 mm I.D., 0.25 µm

76

543

2

1

76

543

2

1

12.0

9

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Figure 5. Aromatics in Reformulated Gasoline; Last Analyte to Elute is 1-Methylnaphthalene (1 mN)

TCEP (1 mN elutes at 39.4 min)60 m x 0.25 mm I.D., 0.44 µm

SLB-IL111 (1 mN elutes at 14.7 min)60 m x 0.25 mm I.D., 0.20 µm

B

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Figure 6. Esters and Ethers; 40 ºC (4 min), 8 ºC/min to 200 ºC (5 min)

SLB-IL6030 m x 0.25 mm I.D., 0.20 µm

PEG30 m x 0.25 mm I.D., 0.25 µm

1. Methyl formate2. Ethyl formate3. Methyl acetate4. Tetrahydrofuran5. Ethyl acetate6. Isopropyl acetate7. n-Propyl acetate8. Isobutyl acetate9. 1,4-Dioxane

10. n-Butyl acetate11. Isoamyl acetate12. n-Amyl acetateC. Contaminant

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1

2, 3 5

4

67

108

9

11

12

642 8 10Time (min)

1

1 5

4

6 7

108

9

11

12

23

C

642 8 10Time (min)

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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 260 ºC

Poly(cyanopropylphenyl)siloxane30 m x 0.25 mm I.D., 0.20 µm

60 ºC (1 min), 8 ºC/min to 230 ºC

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1

23 4

5

8

6

7

12

119

15

16

1413

2120 19

23

22 26252429

28

27

31

3032 33 34

35

36

3738

36 min

10 20 30

Min

18

17

Figure 8. Fatty Acid Methyl Esters (FAMEs); 170 ºC, 1 ºC/min to 225 ºC

SLB-IL6030 m x 0.25 mm I.D., 0.20 µm

PEG30 m x 0.25 mm I.D., 0.25 µm

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16. C18:017. C18:1n9c18. C18:1n9t19. C18:2n6c20. C18:2n6t21. C18:3n622. C18:3n323. C20:024. C20:1n925. C20:226. C20:3n627. C21:028. C20:3n329. C20:4n630. C20:5n331. C22:032. C22:1n933. C22:234. C23:035. C22:5n336. C24:037. C22:6n338. C24:1n9

1. C4:02. C6:03. C8:04. C10:05. C11:06. C12:07. C13:08. C14:09. C14:1

10. C15:011. C15:112. C16:013. C16:114. C17:015. C17:1

16

2120 19

18

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Figure 9. FAMEs in B20 Biodiesel; 50 ºC, 13 ºC/min to 270 ºC (5 min)

SLB-IL11130 m x 0.25 mm I.D., 0.20 µm

PEG30 m x 0.25 mm I.D., 0.25 µm

No overlap of hydrocarbon and FAME fractions

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Figure 10. Chlorinated Solvents; 40 ºC (4 min), 8 ºC/min to 200 ºC (5 min)

1. 1,1-Dichloroethylene2. trans-1,2-Dichloroethylene3. Carbon tetrachloride4. 1,1,1-Trichloroethane5. 1,1-Dichloroethane6. Methylene chloride7. Trichloroethylene8. Tetrachloroethene9. Chloroform

10. 1,2-Dichloroethane11. 1,1,1,2-Tetrachloroethane12. 1,1,2,2-Tetrachloroethane

SLB-IL6030 m x 0.25 mm I.D., 0.20 µm

PEG30 m x 0.25 mm I.D., 0.25 µm

11

15

1

5

46 7 10

89 11

12

2

3

5

4

3

642 8 10 12Time (min)

13, 4

5

6

7 108

9

11 12

2

642 8 10 12Time (min)

14 16

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Figure 11. Native Spearmint Essential Oil; 75 ºC (4 min), 4 ºC/min to 200 ºC (10 min)

SLB-IL6030 m x 0.25 mm I.D., 0.20 µm

PEG30 m x 0.25 mm I.D., 0.25 µm

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0 10 20 30 40Min

0 10 20 30

Min

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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.

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Equity, SLB SP, SPB, and SUPELCOWAX is a registered trademarks of Sigma-Aldrich Co. LLC.

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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 65–191.

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.

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Equity, SLB, SP, SPB, and SUPELCOWAX are registered trademarks of Sigma-Aldrich Co. LLC.

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Thank You

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