Submitted to: Phytochemical Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2009
Publication Date: 8/1/2009
Publication URL: http://handle.nal.usda.gov/10113/58497
Citation: Lucero, M.E., Estell, R.E., Tellez, M., Fredrickson, E.L. 2009. A retention index calculator simplifies identification of plant volatile organic compounds. Phytochemical Analysis. 20:378-384. Interpretive Summary: Volatile chemicals released by desert shrubs interact with herbivores, endophytes, pathogens, and pollinators. Because a single plant may release tens to hundreds of different volatile chemicals, identification can be challenging. Typical approaches include mass spectroscopy and retention index matching. This paper describes a calculator which determines retention indices for volatile compounds, and a library of retention indices obtained from shrub volatiles gathered in the Chihuahuan Desert of North America. The calculator's utility is demonstrated by analyzing volatiles released by the desert shrub, Koberlinia spinosa. The calculator and library are provided as supplemental data.
Technical Abstract: Plant volatiles (PVOCs) are important targets for studies in natural products, chemotaxonomy and biochemical ecology. The complexity of PVOC profiles often limits research to studies targeting only easily identified compounds. With the availability of mass spectral libraries and recent growth of retention index (RI) libraries, PVOC identification can be achieved using only gas chromatography coupled to mass spectrometry (GCMS). However, RI library searching is not typically automated, and until recently, RI libraries were both limited in scope and costly to obtain. Objective is to automate RI calculation and lookup functions commonly utilized in PVOC analysis. Formula required for calculating retention indices from retention time data were placed in a spreadsheet along with lookup functions and a retention index library. Retention times obtained from GCMS analysis of alkane standards and Koeberlinia spinosa essential oil were entered into the spreadsheet to determine retention indices. Indices were used in combination with mass spectral analysis to identify compounds contained in Koeberlinia spinosa essential oil. Eighteen compounds were positively identified. Total oil yield was low, with only 5 ppm in purple berries. The most abundant compounds were octen-3-ol and methyl salicylate. The spreadsheet accurately calculated RIs of the detected compounds. The downloadable spreadsheet tool developed for this study provides a calculator and RI library that works in conjunction with GCMS or other analytical techniques to identify PVOCs in plant extracts.