Quantitative High Performance Liquid Chromatography Determination of Alkanolamines in Ionic Liquid Absorbents

Abstract

The development of modern absorption media suitable for CO₂ scrubbing, such as ionic liquids and their mixtures, requires appropriate analytical protocols. In this paper, the application of high-performance liquid chromatography to the determination of alkanolamine at various concentrations in ionic liquid solutions was investigated. Both hydrophilic and hydrophobic commercial ionic liquids, such as 1-butyl-3-methylimidazolium acetate [bmim][OAc], 1-ethyl-3-methylimidazolium octylsulfate [emim][OcSO₄], and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [bmim][NTf₂], were studied in this paper and different sample preparation procedures were used for each class of solvent. A simple extraction step was necessary prior to HPLC analysis for hydrophobic ionic liquids. This step was performed using five times more 0.05 M KH₂PO₄ than needed for the ionic liquid sample. Hydrophilic ionic liquid solutions could be analyzed after diluting the sample with water. The general procedure involved separation at room temperature using a cation-exchange HPLC with 0.05 M KH₂PO₄ as the mobile phase and refractometric detection without derivatizing the amines. The influence of the temperature and mobile phase composition on alkanolamine retention was investigated. The relationship between the peak area and alkanolamine concentration was linear over 3 orders of magnitude (2–200 nmol). The detection limit (LOD) for monoethanolamine (MEA) and diethanolamine (DEA) was 1.5 and 2 nmol, respectively. For hydrophobic ionic liquids, which require extraction, it was possible to analyze a 0.004% MEA solution. The quantity of the sample required for analysis was 0.1 g, and the analysis time did not exceed 20 minutes.

Keywords:

• Alkanolamines
• Ionic chromatography
• Ionic liquids
• Refractive index detection

Acknowledgments

The results presented in this paper were obtained from research work co-financed by the National Centre of Research and Development in the framework of Contract SP/E/1/67484/10, Strategic Research Program, Advanced Technologies for Energy Generation: Development of a technology for highly efficient zero-emission coal-fired power units integrated with CO₂ capture.

Notes

Note: Each sample was injected three times and three sets of the samples were prepared (nine analyses for each solution).

^a fraction of initial mixture corresponding to the 4 µL of injection taken from supernatant, total sample amount of 3% solution used = 0.17 g.