Comparison of the Selectivity of Ionic Liquid - Sigma-Aldrich

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Comparison of the Selectivity of Ionic Liquid Stationary Phases for the Analysis of FAME Isomers

T413035

L.M. Sidisky, G.A. Baney, J.L. Desorcie,K.K. Stenerson, and D.L. ShollenbergerSupelco, Div. of Sigma-AldrichBellefonte, PA 16823 USA


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Abstract

Analyses of fatty acid methyl esters (FAMEs) are continuing to gain importance as more research is focusing on their biomedical impacts. This includes the analysis of saturated and polyunsaturated FAMEs along with the positional geometric (cis and trans) FAME isomers. Traditionally, FAME analyses have been performed using silicone polymer or polyethylene glycol based stationary phases that yield typical elution patterns. Analysts performing the task of analyzing the fatty acid composition of food have a wide variety of capillary column selectivitys available for resolving the fatty acids as FAMEs depending upon the information they require from their analyses. Nonpolar methyl silicone columns provide a boiling point separation of the FAME isomers with limited resolution of polyunsaturated isomers. Polar polyethylene glycol (PEG) columns resolve the isomers by degree of unsaturation with minimal overlap of the carbon chain lengths. The highly polar cyanosilicone columns will resolve cis and trans isomers along with possibly providing positional geometric isomer separations depending upon the column type.


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Abstract (contd.)

New classes of stationary phases based on Ionic Liquid technology have been developed and have demonstrated to provide unique elution patterns for FAME isomers compared to the traditional silicone or polyethylene glycol based stationary phases. The two new phases are SLB®-IL60 with a PEG like selectivity and the SLB-IL111 with highly polar selectivity. We will compare and contrast the selectivity of the ionic liquid phases with polymeric based phases for various FAME samples.


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Ionic Liquids: Example Structure

• Benefits• Offer greater stability compared to polysiloxane polymers and polyethylene glycols

– Lower column bleed, longer life, and higher thermal limits– More resistant to damage from moisture/oxygen

• Numerous combinations of cations and anions are possible allowing for “tailored”selectivity, application, or function

– Dicationic (shown) or polycationic

– Cations, linkages, and/or anions can be changed

– Pendant groups can be added to cations and/or linkages

SLB-IL100

1,9-di(3-vinylimidazolium) nonane bis(trifluoromethyl) sulfonyl imidate


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Experimental - Selectivity Evaluations

Rapeseed Oil FAMEsRapeseed oil is a simple vegetable oil that contains a series of saturated and unsaturated fatty acids ranging from C14 through C24 in carbon number. The composition of the mix is:

1. Myristic (C14:0) 1.0%2. Palmitic (C16:0) 4.0%3. Stearic (C18:0) 3.0%4. Oleic (C18:1n9c) 60.0%5. Linoleic (C18:2) 12.0%6. Linolenic (C18:3) 5.0%7. Arachidic (C20:0) 3.0%8. cis-11-Eicosenoic (C20:1) 1.0%9. Behenic (C22:0) 3.0%

10. Erucic (C22:1) 5.0%11. Lignoceric (C24:0) 3.0%


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column: SLB-IL columns, 30 m x 0.25 mm I.D., 0.20 µmoven: 180 °C isothermal

inj.: 250 °C det.: FID, 250 °C

flow rate: helium, 25 cm/sec constantinjection: 1.0 µL, split 100:1

liner: 4 mm I.D. cup splitsample: Rapeseed oil FAME mix (O7756-1AMP) diluted

to 10 mg/mL in methylene chloride

Column Selectivity Conditions


70 10 20 30 40 50 60 70

Time (min)

1

2

3

4

5

6

8

79 11

10

Column SelectivitySLB-IL60, 30 m x 0.25 mm I.D., 0.20 µm (29505-U)


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1.0 2.0 3.0 4.0 5.0 6.0 7.0Time (min)

1

2

3

45

6,9

8

7

11

10

Column Selectivity SLB-IL111, 30 m x 0.25 mm I.D., 0.20 µm (28927-U)


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Column Selectivity FAME Equivalent Chain Length (ECL) Values

22.14 20.15 19.04 18.54 18.17 SLB-IL60

* Values determined @ 190 °C23.01 21.07 22.00 20.48 19.10 SLB-IL11122.72 20.72 20.82 19.71 18.73 SLB-IL100

22.55 20.55 20.34 19.39 18.58 SLB-IL82

22.43 20.42 19.84 19.08 18.45 SLB-IL76

22.17 20.17 19.14 18.60 18.20 SLB-IL61

22.14 20.14 19.03 18.53 18.17 SLB-IL59

22.57 20.63 20.63 19.59 18.69 SP™-2380*

22.19 20.22 19.38 18.72 18.25 SUPELCOWAX® 10*

C22:1n9C20:1n9C18:3n6C18:2n6cC18:1n9c

FAME ECL Values @ 180 °C

The ECL Values compare the selectivity of the various columns. As the columns become more polar, the ECL value increases. The increased polarity also results in overlap of the carbon chain lengths especially with the highly polar SLB-IL100 and SLB-IL111.


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cis/trans FAME Isomerscolumn: SP-2560, 100 m x 0.25 mm I.D.,

0.20 µm (24056)oven: 180 °C isothermal

inj.: 250 °Cdet.: FID, 250 °C

carrier gas: hydrogen, 1 mL/min.injection: 1 µL, 100:1 split

liner: 4 mm I.D., split liner with cup (2051001)

column: SLB-IL111, 100 m x 0.25 mm I.D., 0.20 µm (29647-U)

oven: 168 °C isothermalinj.: 250 °C

det.: FID, 250 °C carrier gas: hydrogen, 1 mL/min.

injection: 1 µL, 100:1 splitliner: 4 mm I.D., split liner with cup (2051001)


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These figures demonstrate the selectivity of the SLB-IL111 compared to the conventional SP-2560 column for the analysis of positional geometric FAME isomer analysis. The SLB-IL111 offers a complimentary selectivity to the SP-2560 column for this analysis.

cis/trans FAME Isomers (contd.)


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Temperature Effects


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SLB-IL111- cis/trans FAME Mix @ 150 °C

0 10 20 30 40 50 60 70Time (min)

26 28 30 32 34 36 38 40Time (min)


14


0 10 20 30 40 50Time (min)

24 26 28 30 32 34Time (min)


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0 10 20 30 40 50 60 70 80Time (min)

30 32 34 36 38 40 42 44Time (min)

Highly polar stationary phases are known to be temperature sensitive. These three figures demonstrate the peak shifting that can occur over an 8 ºC temperature range.


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cis/trans FAMEs


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C18:1n9 cis/trans FAMEs @ 180 °C

11.0 12.0 13.0 14.0 15.0Time (min) 21.0 22.0 23.0 24.0

Time (min)

SLB-IL60 PEG

transcis


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C18:2n6 cis & trans FAME Isomers @ 180 °C

10 12 14 16 18 20Time (min)

26 28 30 32 34Time (min)

SLB-IL60 PEG C18:2n6 tt

C18:2n6 ttC18:2n6 cc

C18:2n6 cc

Traditional polyethylene glycol phases (PEG) are known to provide cis & trans isomer separation with the cis isomer eluting prior to the trans isomer. The SLB-IL60 ionic liquid column (with a PEG like polarity) offers a unique selectivity for cis and trans isomer separations as the trans isomer elutes prior to the cisisomers.


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Fish Oil FAME Analysis


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GC Analysis Conditions

columns: Omegawax™ 250, 30 m x 0.25 mm I.D., 0.25 µmSLB-IL60, 30 m x 0.25 mm I.D., 0.20 µm

oven: 170 °C, 1 °C/min. to 225°C inj.: 250 °C

det.: FID, 260 °Ccarrier gas: helium, 1.2 mL/min constant flow

injection: 1 µL, 100:1 split liner: 4 mm ID FocusLiner™ w/taper

GC analysis conditions are from methods AOAC 991.39 and AOCS CE-1i-07.


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PUFA 3 Standard

C14:0 C16:0 C16:1n7

C16:2n4C16:3n4

C18:0

C18:1n9

C18:1n7

C18:2n6

C18:3n4

C18:3n3

C18:4n3

C20:1n9C20:3n3

C20:4n6

C20:5n3 , C20:4n3 C22:6n3

C22:5n3

10 20 30Time (min)

SLB-IL60

10 20 30 40 50Time (min)

C18:2n6

C14:0

C16:0

C16:1n7

C16:2n4C16:3n4

C18:0

C18:1n9

C18:1n7

C18:3n4

C18:3n3

C18:4n3

C20:1n9 C20:3n3

C20:4n6

C20:4n3

C20:5n3

C22:5n3

C22:6n3

Omegawax 250


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Extract of Fish Oil Capsule

Omegawax 250

SLB-IL60

10 20 30 40 50Time (min)

C14:0

C16:0

C16:1n7

C16:2n4

C16:3n4C18:0

C18:1n9C18:1n7

C18:2n6

C18:3n4

C18:3n3

C18:4n3C20:1n9

C20:3n3C20:4n3

C20:5n3

C22:5n3

C22:6n3

10 20 30Time (min)

C16:3n4

C14:0 C!6:0

C16:1n7

C16:2n4

C18:0

C18:1n9

C18:1n7

C18:2n6

C18:3n4C18:3n3

C18:4n3C20:1n9C20:3n3

C20:5n3, C20:4n3

C22:6n3

C22:5n3

Anchovy and sardine listed as fish sources on product label

Samples prepared using AOAC Method 991.39


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Extract of Farm-Raised Atlantic Salmon

10 20 30 40 50Time (min)

C14:0

BHT C16:0

C16:1n7

C16:2n4C16:3n4

C18:0

C18:1n9

C18:1n7

C18:2n6

C18:3n6

C18:3n4

C18:3n3C18:4n3

C20:1n9 C20:3n3C20:4n6

C20:4n3

C20:5n3

C22:5n3

C22:6n3

Omegawax 250

10 20 30Time (min)

C18:3n4

C20:4n6

C14:0

C16:0

C16:1n7

C16:2n4C16:3n4C18:0

C18:1n9

C18:1n7

C18:2n6

C18:3n6

C18:3n3C18:4n3

C20:1n9C20:3n3

C20:5n3C20:4n3

C22:1n9

C22:6n3C22:5n3

SLB-IL60

Samples prepared using AOCS Official Method Ce 1k-09; BHT added as an antioxidant


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These fish oil analyses compare the selectivity of the SLB-IL60 and the Omegwax 250 columns. The columns show similar selectivity for many of the separations. The SLB-IL60 shows a very unique selectivity for some of the longer chain FAME isomers as demonstrated by the C22:6n3 isomer eluting prior to the C22:5n3 isomer. We are still working to determine the mechanism for this unique elution pattern.


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Summary

A series of polar and highly polar Ionic Liquid stationary phases have been evaluated.Changing the functionality of the cation or anion group will change the selectivity of the IL phase.The GC column polarity scale demonstrates that the Ionic Liquid stationary phases are typically polar to highly polar. A new phase SLB-IL111 is the most polar phase commercially available.Highly Polar SLB-IL111 Ionic Liquid capillary columns provide a complimentary separation of positional geometric FAME isomers compared to the SP-2560 columns.Highly polar stationary phases are temperature sensitive. The new polar SLB-IL60 offers unique cis/ trans FAME separations compared to PEG phases along with unique separation of other FAME isomers.


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Trademarks

SLB and SUPELCOWAX are registered trademarks of Sigma-Aldrich Co. LLC.Omegawax and SP are trademarks of Sigma-Aldrich Co. LLC.FocusLiner is a trademark of SGE Analytical Science Pty. Ltd.


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Thank You

Date post:	15-Feb-2022
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Comparison of the Selectivity of Ionic Liquid - Sigma-Aldrich

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