Optimizing loop-type cryogenic modulation in comprehensive two-dimensional gas chromatography using time-variable combination of the dual-stage jets for analysis of crude oil

• Published in: Journal of Chromatography A 2018-02, Vol.1536, p.82-87
• Main Authors: Alexandrino, Guilherme L., de Sousa, Gustavo R., de A.M. Reis, Francisco, Augusto, Fabio
• Format: Article
• Language: English
• Subjects: Comprehensive two-dimensional gas chromatography; Crude oil; Experimental design; Loop-type cryogenic modulator; Time-variable dual stage jet
• ISSN: 0021-9673
• DOI: 10.1016/j.chroma.2017.10.054

•Modulation plays the central role to enhance the analytical performance in GC×GC.•Loop-type cryogenic modulators are commonly used in GC×GC analysis of crude oil.•Tuning the dual-stage jets in GC×GC is difficult for complex samples like crude oil.•A time-variable combination of the dual-stage jets is proposed to handle modulation.•DoE was used to optimize the setting of the dual-stage jets along the GC×GC analysis. The enhanced chromatographic capability of the comprehensive two-dimensional gas chromatography (GC×GC) has already found several applications in analytical chemistry comprising complex samples. However, setting the appropriate chromatographic conditions that maximize sensitivity and separation efficiency in GC×GC may be more difficult than in conventional one-dimension gas chromatography, mainly due to the additional parameters strictly related to the modulation. Loop-type cryogenic modulators have been currently used for crude oil analysis using GC×GC, requiring sometimes a laborious try-and-error procedure to properly tune the dual-jets elapsed times on modulation. In this work, the advantages of choosing a time-variable combination of cold and hot jets pulses in a loop-type cryogenic modulator is presented when performing the fingerprinting analysis of crude oils using GC×GC-QMS, contrary to the conventional procedure based on a single combination for the dual-stage jets. A design of experiments approach is proposed to most effectively optimize the time-variable combination of the dual-jets elapsed times while modulating the wide hydrocarbons range along the GC×GC analysis. The most abundant classes of hydrocarbons contained in the maltenes fraction of a crude oil sample, such as paraffins, aromatics, steranes and hopanes were successfully resolved.