Innovative Solutions for Your Toughest Separations:
Ionic Liquid Capillary GC Columns

Lisa Battle (McCombie)  Product Manager, GC & Carbons

Gas chromatography has been used for decades with continuous phase development. Most updates have been based on polymeric materials, but a new page was turned with the introduction of the Ionic Liquid (IL) columns, which offer new selectivity and application options. Arguably one of the most exciting Ionic Liquid Capillary columns is the Watercol™ column. This column allows the qualitative and quantitative determination of water in a variety of matrices by GC, eliminating the need for special testing. It is particularly handy for gaseous samples (Figure 1).

 

Figure 1. Chromatogram for water determination (25 ppm) in LPG. Limit of Quantification (S/N=10) and Limit of Detection (S/N=3.3) can be down to 0.66 ppm and 0.22 ppm respectively (courtesy of Shimadzu, see also Analytix Reporter Issue 2).

Chromatogram for water determination (25 ppm) in LPG

Instrument  
gas chromatograph: Tracera (GC-2010 Plus A + BID-2010 Plus)
sample injection: Valco Internal Liquid Sample Injector with Splitter Injection Unit
gas purifier: Supelco High Capacity Gas Purifier (Cat. No. 29541-U)
Analysis Conditions  
column: Watercol™ 1910, 30 m x 0.25 mm I.D., 0.20 µm (Cat. No. 29711-U)
oven: 35 °C (2 min), 5 °C/min to 150 °C (15 min)
carrier gas: Helium 45 cm/sec (Column flow rate 3.78 mL/min)
inj. volume: 2 μL
split: 5:1
transfer line temp.: 175 °C (After internal liquid sample injector to GC column oven)
detector temp.: 200 °C
discharge gas vol.: 50 mL/min (He)

 

Looking into ASTM D3606: Standard Test Method for Determination of Benzene and Toluene in Spark Ignition Fuels by Gas Chromatography, an IL column alternative is available, the SLB®-ILD3606 column. This column allows the complete resolution of aromatics and oxygenates in reformulated gasoline on one column (Figure 2), and by that, significantly reduces analysis time and improves results.

 

Figure 2. Oxygenate resolution in reformulated gasoline.

column: SLB®-ILD3606, 60 m × 0.25 mm I.D., 0.20 μm (Cat. No. 29691-U)
oven: 50 °C (6 min), 15 °C/min to 265 °C (10 min)
inj. temp.: 250 °C
detector: FID, 250 °C
carrier gas: helium, 21 cm/sec
injection: 1 μL, 100:1 split
liner: 4 mm I.D., split type, cup design
sample: reformulated gasoline (contains 10% ethanol) with 7 other oxygenates added (at 2.5-5%)

Oxygenate resolution in reformulated gasolineOxygenate resolution in reformulated gasoline

 

Supelco also provides several other IL columns, which include the SLB®-ILPAH for high resolution PAH analysis (Figure 3) and also the new improved i Series (SLB®-IL60i, SLB®-Il76i, SLB®-IL111i) with unique selectivity paired with higher inertness. These i-series columns have applications in various fields such as petroleum, food and chemical analysis, and can provide reliable and reproducible results. The SLB®-IL60i has a polarity similar to PEG/Wax phases, while the SLB®-IL111i is the highest polarity GC phase currently available, and can offer benefits in the determination of unsaturated fatty acid methyl ester (FAME) isomers.

 

Figure 3. ILPAH resolution of critical groups in a 22-component PAH mix.

column: SLB®-ILPAH, 20 m × 0.18 mm I.D., 0.05 µm (Cat. No. 29799-U)
oven: 90 °C (6 min), 20 °C/min to 225 °C, 5 °C/min to 300 °C (10 min)
inj. temp.: 300 °C
detector: FID, 310 °C
carrier gas: hydrogen, 1.3 mL/min, constant flow
injection: 1 µL, 50:1 split
liner: 4 mm I.D., split type, cup design
sample: 10 PAHs, each at 100 µg/mL in methylene chloride

ILPAH resolution of critical groups in a 22-component PAH mixILPAH resolution of critical groups in a 22-component PAH mix

Background on ionic liquid technology

In 2005, Prof. Daniel W. Armstrong (University of Texas at Arlington) showed that dicationic and polycationic ionic liquids could successfully be used as viable GC stationary phases. These phases consist of two or more organic cations joined by a linkage and associated with anions, which can be either inorganic or organic. Ionic liquid phases differ physically and chemically from traditional GC stationary phases:

  • The molecules in stationary phase are much smaller compared to big, bulky polysiloxane polymer and polyethylene glycol phases, plus there are no active hydroxyl groups. These features lead to greater stability, even in the presence of moisture and/or oxygen.
  • Many modifications are possible in order to alter selectivity. The base structure can be dicationic or polycationic. There are numerous cation, linkage, and anion choices. Pendant groups can be added to cations and/or linkages.

These columns have the opportunity to impact current practices in several ways:

  • Columns can be engineered with similar selectivity & polarity to non-ionic liquid columns, but with higher operating temperatures and less susceptibility to be damaged by moisture and/or oxygen, hence, they are ideal for GC-MS.
  • Columns can be engineered with completely unique selectivity to non-ionic liquid columns, or polarities not available before (e.g., SLB®-IL111i, which is more polar than TCEP), and produce good peak shape and resolution for compounds of varying functionality.
  • Columns can be used in multidimensional separations, due to their engineered orthogonality and high thermal stability.

Materials