Detailed analysis of hydrocarbon groups in diesel range petroleum fractions with on-line coupled supercritical fluid chromatography–gas chromatography–mass spectrometry

Abstract

A supercritical fluid chromatographic column was coupled to a capillary gas chromatography (GC) system, corresponding to a two-dimensional separation scheme. The good compatibility of supercritical fluid extraction (SFC) with GC is emphasised: a simple coupling device including a heart-cut valve, a T-piece and a restricted capillary transfer-line was necessary. The system was applied to the analysis of diesel-range petroleum fractions to obtain a more detailed characterisation of these types of samples. Group-type separation of the samples was performed by SFC using a silica-packed column, according to ASTM method D 5186-95. The eluate was monitored with flame ionisation and UV diode array detectors. The separated groups were then transferred to the GC column for detailed analysis. Compounds separated with capillary GC were identified using mass spectrometry (MS). The SFC–GC–MS analysis carried out on a fluid catalytic-cracking product resulted in characterisation of the compounds present in diaromatic and polyaromatic groups, while identification of peaks in the saturate and monoaromatic groups was not possible because of the coelutions of the huge number of components present in these fractions. Results achieved by the SFC–GC–MS system are similar to those provided by LC–GC, but the great advantage of the SFC–GC system is that the SFC solvent (CO 2) can be easily eliminated and has no disturbing effect on the GC separation and detection.