Enhancing terpene and other plant volatiles analysis – A free spreadsheet tool “Retentify” for GC–MS data processing

Abstract

Despite significant progress in gas chromatography-mass spectrometry (GC–MS), misidentifications still occur, especially in untargeted analyses of complex samples of plant origin. In addition to using reference materials, a common approach to confirm identifications is to employ linear retention indices (LRIs). Ideally, when LRI validation is made automatically by the software using accurate library data. However, present solutions in this area either require additional payment or have many constraints. As a result, reference LRIs are often not included in search algorithms, or if they are, library LRI values may not be matched to the selectivity of the column used. Many GC–MS analyses are conducted without LRI comparison, or the comparison is performed after an MS library search. Such a manual examination is highly laborious, especially for datasets containing hundreds or more components. Therefore, an easy-to-use spreadsheet tool was developed to be used after an MS library search. The tool called Retentify, among other features, can: (1) calculate the experimental RIs, (2) retrieve automatically reference RIs from the reliable compilation of Babushok et al. (NIST), considering an appropriate selectivity of the column, (3) compute experimental LRIs errors and indicate the potential mismatch in the red/yellow/green color scale. Retentify is thoroughly described and demonstrated in the analysis of true lavender (Lavandula angustifolia) essential oil. The uniqueness of this tool lies in its reliance on highly accurate, averaged retention data provided by NIST, automatic input of reference LRIs based on CAS, and visuals to help LRI evaluation. The tool is easy to use and requires no financial and minimal time investment to learn, making it accessible to any researcher without specialization in plant volatile analysis.