Ionic Liquids by IC–MS

Leo (Jinyuan) Wang and William C. Schnute, Dionex Corporation

The characteristic composition of ionic liquids (an organic cation or anion and a counterion, in either organic or inorganic form) exhibits unique properties, such as extremely low vapor pressure, excellent thermal stability, electrical conductivity, high polarity, and miscibility with various types of solvents. Ionic liquids are organic salts with relatively low melting points (below 100 °C) and have been used as solvents in catalysis, organic chemistry, electrochemistry, and separation science.

Here, an ion chromatographic mass spectrometric (IC-MS) profile method for the quantitative determination of anionic ionic liquids and anions in a single chromatographic run is presented.

Experimental

System: ICS-2000 RFIC™ system

Column: IonPac® AS20 and AG20 (2 mm)

Mobile phase: Hydroxide gradient

Flow rate: 250 µL/min

Inj. volume: 20 µL

Detection: Suppressed Conductivity and MSQ Plus™ mass spectrometer

Ionization interface: Electrospray Ionization (ESI)

Detection mode: Selected Ion Monitoring (SIM)

Probe temperature: 500 °C

Needle voltage: 1.0 kV

Nebulizer gas: Nitrogen at 85 psi

Results

Figure 1 shows the chromatographic separation of 16 analytes. The SIM chromatograms indicate the differentiation of closely eluted analytes and are shown as single peaks in each SIM channel.

Figure 1

Quantitative experiments provided coefficients of determination (r² ) > 0.99 for each analyte in the calibration range from low ppb level to 1000 ppb. Method detection limits ranged from 1.04 ppb (tosylate) and 6.13 ppb (sulfate). Three commercially available ionic liquids (dissolved in DI water at 2 mg/mL) were analyzed for impurities by this IC-MS method. Chloride (present in two of the three samples) and bromide (present in all samples) were observed as the major impurities. Other anion impurities such as acetate, methanesulfonate, nitrate, and sulfate were also detected in some or all samples.

IonPac is a registered trademark and RFIC is a trademark of Dionex Corporation.

MSQ Plus is a trademark of Thermo Fisher Scientific, Inc.

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