Evaluation of a prototype reverse fill/flush flow modulation-splitter system for the highly detailed separation required in industrial settings

Abstract

Reverse fill/flush (RFF) differential flow modulators are a lower cost, consumable free, robust option to achieve comprehensive two-dimensional gas chromatography (GC × GC) with FID and MS dual detection. For the required highly detailed separation of all hydrocarbon classes for a petroleum industry setting thermal-based modulators are considered the “gold standard” for their high performance, but there are substantial costs involved. In an industrial setting, there is a necessary balance between the separation performance, cost of instrumentation and costs of operation. It is uncertain if an RFF modulator chromatographic performance is sufficient to achieve the demands of an industrial research laboratory as a cost-effective alternative to thermal modulation. This paper reports an evaluation of the capabilities of a new prototype RFF flow modulator with flow splitter system and its chromatographic performance relative to thermal modulation for detailed hydrocarbon analysis. The prototype RFF modulator splitter system was easy to use with straightforward method optimization due to the lack of restrictors and implementation of back pressure regulation for variable restriction. It also provided good peak shapes, accurate quantification, and maintained constant split to both detectors throughout the analysis. The data processing workflow was greatly improved with the alignment of the MS and FID traces in the software. However, the chromatographic performance of the RFF was found to be less and insufficient for detailed hydrocarbon analysis when compared to thermal modulation. The greatest discrepancy was found in the differentiation of the saturate class, specifically the alkanes, iso-alkanes, and cycloalkanes from each other and other monoaromatics. A comparable separation was found in the lower carbon range of C₇-C₁₄ while the region of C₁₆-C₂₂ was challenging for the RFF modulator. Overall, the detailed analysis of a middle distillate was found to be too complex for the RFF flow modulator in comparison to thermal modulator.