Headspace gas-chromatography is the method of analysis of volatiles in the system, when after equilibration at a certain temperature, the sample is taken form the gas phase above the liquid. This way, it is possible to trace what would evaporate from the sample during heating, but also analyse comparatively volatile impurities in the samples. Normally the analysis object is first dissolved in suitable solvent, in order to make the system homogenous and release the volatiles that might have been trapped in a solid matrix. Hence, the temperatures at which analysis is performed are restricted by the boiling point of the solvent used.
The unique combination of properties of ionic liquids makes them candidate of choice for the solvent in GC-Headspace sampling. Those properties include:
- First and foremost, ultralow vapour pressure, which almost entirely prevents contamination of the gaseous phase with residues of the solvent used, allowing wide detection window. Furthermore, the safety of operation is also improved by virtue of the non-volatile nature of ILs, as at higher temperatures no pressure build-up occurs.
- Good thermal stability and wide liquid range, allowing analysis in a wide temperature range, and most importantly at high temperatures where organic solvents are not usable anymore. At those higher temperatures medium and high-boiling species could be analysed.
- High solubilizing power broadens the horizons of application for analytes and matrices combinations that were not possible before. Furthermore, if simplifies the operation procedures, avoiding pre-treatments, like extraction. For example, ionic liquids that can dissolve cellulose-based material pave the way towards simple determination of impurities in pharmaceutical formulations, when cellulose-based matrices are used, by simply dissolving the entire formulation.
- Use of ionic liquids often results in much lower limits of detection (LOD) and therefore more sensitive methods of analysis, compared to usual solvents, like DMSO or DMAC. As a consequence, analysis can be completed with smaller sample volumes.
- Tuneable nature of ILs means that it is possible to find the right IL for almost any requirements.
Scheme 1. GC headspace with ILs as solvents.
All abovementioned allows to analyse a wide spectrum of compounds in different matrixces, for example water, process impurities, volatile organic compounds (VOCs) and residual solvents in active pharmaceutical ingredients (API). Ability no analyse comparative high boiling compounds, like some amines or alkylating agents gives ILs a big advantage compared to solvents like DMSO. Furthermore, since ILs have the ability to solubilize many difficult-to-dissolve materials, like cellulosic materials for example, their use as solvents opens an easy way for analysis of complex systems, e.g. ready-to-use pharmaceutical formulations: the entire pills can be dissolved and analysed, doing away with pretreatment and extractions, which not only taking time, but also increase the risk of contamination of the sample and loss of the analyte during pretreatment.
For the selection of ILs that can perform well as GC Headspace solvents in your specific application, please contact us. We will be happy to advice you on the choice of the right product or make a customized product for you.
Text and illustration: Dr. Svetlana Cadu, Iolitec 2019.