Distinguishing C8 alkane isomers: Application of TSE-PSYCHE and CSSF TOCSY NMR techniques

The composition of hydrocarbon fuels, particularly C8 alkane isomers, has a profound impact on their combustion characteristics. Even with same carbon number, the varying degrees of branching can significantly influence these properties. Thus, qualitative and quantitative analyses of C8 fuel components is essential. However, due to highly their structural similarities and analogous physicochemical properties, analyzing these components by chromatographic methods is often a tedious and challenge task. Here, we introduce novel NMR methods utilizing TSE-PSYCHE and CSSF TOCSY NMR technology to qualitatively and quantitatively analyze a mixture of all 16 isomers of octane. These methods have successfully achieved virtual separation of 14 components, a significant feat considering the potential for overlap in conventional ¹H NMR analysis. Moreover, employing 2,2,4-trimethylpentane as a typical compound, the application of the quantitative analysis method was illustrated. By determining the LOD at 0.6 mM and the LOQ at 1.2 mM for this C8 compound, the sensitivity and applicability of the approach were demonstrated. The accuracy was confirmed with biases ranging from 1.5 % to 7 %, and the precision was evidenced by a relative standard deviation (RSD) of 4.1 %. These measurements underscore the method’s reliability and precision in quantifying components within complex hydrocarbon mixtures.