Polyionic Ionic Liquid GC Stationary Phase Evaluations

Importance of the Topic

The development of ionic liquid stationary phases offers unprecedented flexibility in gas chromatography by combining a variety of cation–anion pairs to tailor polarity, selectivity and thermal stability. These new phases address challenges in separating geometric and positional isomers, complex mixtures of fatty acid methyl esters, polycyclic aromatic hydrocarbons, trace water and volatile organic compounds in diverse samples.

Objectives and Study Overview

The primary aim was to evaluate a series of highly polar and ultra-polar ionic liquid GC phases (SLB-IL100, SLB-IL76, SLB-IL111, SLB-IL60 and related variants) with respect to:

• Structural characteristics and phase polarity ranking
• Performance in cis/trans FAME separations versus standard cyanopropylsilicone columns
• Analysis of PAHs, water–solvent mixtures and alcoholic beverages
• Orthogonal selectivity in comprehensive two-dimensional GC (GC×GC) applications

Methodology and Instrumentation

Columns were prepared with various ionic liquid chemistries incorporating imidazolium and phosphonium cations and bis(trifluoromethylsulfonyl)imide anions. Key analytical setups included:

• Single-dimensional GC with flame ionization detection (FID) and thermal conductivity detection (TCD)
• Capillary columns: lengths 20–200 m, internal diameters 0.10–0.25 mm, film thicknesses 0.04–0.20 µm
• Temperature programs spanning ambient to >300 °C
• Carrier gases: helium and hydrogen at constant flow
• Solid-phase microextraction (SPME) using Carboxen fibers
• Comprehensive GC×GC coupled to time-of-flight MS (LECO Pegasus GC×GC/TOFMS)

Main Results and Discussion

• Polarity ranking placed SLB-IL111 as the most polar commercial phase, enabling superior resolution of cis/trans and positional fatty acid isomers compared to SP-2560 columns.
• SLB-IL60 exhibited improved inertness for C1–C12 alcohols, complementary selectivity to polyethylene glycol (PEG) columns and lower bleed at high temperature.
• Ionic liquid phases effectively separated trace water from common solvents (methanol, ethanol, acetone, isopropanol, 1-butanol, dioxane) in programmed runs.
• Application to native essential oils (spearmint, patchouli) and alcoholic beverages (vodka, ouzo, grappa) demonstrated clean separation of volatiles, water and trace contaminants.
• PAH mixtures were resolved on SLB-IL59, with clear distinction of isomeric anthracene/phenanthrene and benzofluoranthene congeners.
• In GC×GC experiments, pairing a polar ionic liquid column with a non-polar secondary or primary column provided orthogonal separation of hydrocarbons, aromatics, PAHs and FAMEs in biodiesel and gasoline samples, achieving fast runs without loss of resolution.

Benefits and Practical Applications

• Tunable selectivity through cation/anion modification allows customization for target analytes.
• Broad thermal range (room temperature to >350 °C) and low volatility ensure robustness under demanding temperature programs.
• High polarity and solvation interactions facilitate separation of geometric isomers and polar compounds.
• Low bleed and chemical inertness enhance sensitivity and peak shape for alcohols and trace organics.
• Orthogonality in GC×GC expands analytical capabilities for complex matrices in environmental, food, petrochemical and beverage analysis.

Future Trends and Potential Uses

• Design of novel ionic liquid chemistries to target emerging contaminants and challenging isomer separations.
• Integration with advanced sample preparation techniques (SPME, thermal desorption) for trace analysis.
• Expansion of GC×GC-TOFMS methods for ultra-complex mixtures in metabolomics, petroleum and environmental forensics.
• Application in automated high-throughput screening and online GC-MS workflows.

Conclusion

Ionic liquid stationary phases represent a versatile and high-performance option for gas chromatography, offering customizable polarity, superior thermal stability and orthogonal selectivity. Their proven advantages in FAME isomer resolution, PAH analysis, water-solvent separation, beverage profiling and GC×GC open new avenues for advanced analytical challenges across multiple industries.

Used Instrumentation

• Agilent/Zebron and Supelco SLB ionic liquid capillary columns
• Gas chromatographs equipped with FID and TCD detectors
• LECO Pegasus GC×GC/TOFMS for two-dimensional separations
• Carboxen SPME fibers for volatile extraction