A Novel Type of Stationary Phase for Gas Chromatography Based on Protonated L-Proline-Xylitol Deep Eutectic Solvent (Des)

Abstract

The paper presents a new kind of stationary phase for gas chromatography based on deep eutectic solvents (DES) in the form of a mixture of L-proline (protonated with hydrochloric acid) as a hydrogen bond acceptor (HBA) and xylitol as a hydrogen bond donor (HBD) in a molar ratio of HBA:HBD 5:1. DES immobilized on a silanized chromatographic support was tested by gas chromatography (GC) in order to determine its resolving power for volatile organic compounds. Studies have shown that this type of DES has very good properties as a stationary phase for GC. Determined Rohrschneider-McReynolds constants reveal that the synthesized DES is a polar stationary phase. The selectivity of DES is influenced by the presence of hydroxyl groups in the xylitol structure capable of forming hydrogen bonds of a donor nature and the proton acceptor properties of the protonated L-proline structure. The presence of additional interactions is brought about by the presence of the carboxyl group. As a result, the retention of alcohols is several times higher than the expected value based on their boiling  points. A significant increase in retention was also found for pyridine derivatives. The developed DES stationary phase is characterized by very good repeatability of retention and stability. The efficiency of the prepared columns and the selectivity of the DES stationary phase are competitive with the commercially available products.

Keywords: NADES, separation techniques, volatile organic compounds (VOCs), hDES, analytical chemistry