Analysis of siloxanes in hydrocarbon mixtures using comprehensive two-dimensional gas chromatography

• Retention indices were used to find effective stationary phases for GC × GC.
• SPB-Octyl × DB-1 stationary phase pair fully separates siloxanes from hydrocarbons.
• GC × GC separations were performed on gasoline spiked with siloxanes.
• Siloxane levels in biogas were determined using iterative trapping and GC × GC.

A comprehensive two-dimensional gas chromatography (GC × GC) method for separating siloxanes from hydrocarbons has been developed using a systematic process. First, the retention indices of a set of siloxanes and a set of hydrocarbons were determined on 6 different stationary phases. The retention indices were then used to model GC × GC separation on 15 different stationary phase pairs. The SPB-Octyl × DB-1 pair was predicted to provide the best separation of the siloxanes from the hydrocarbons. The efficacy of this stationary phase pair was experimentally tested by performing a GC × GC analysis of gasoline spiked with siloxanes and by analyzing biogas obtained from a local wastewater treatment facility. The model predictions agreed well with the experimental results. The SPB-Octyl × DB-1 stationary phase pair constrained the hydrocarbons to a narrow range of secondary retention times and fully isolated the siloxanes from the hydrocarbon band. The resulting GC × GC method allows siloxanes to be resolved from complex mixtures of hydrocarbons without requiring the use of a selective detector.