Determination of Plant Volatiles Using Solid Phase Microextraction GC–MS

Determination of Plant Volatiles Using Solid Phase Microextraction GC–MS

Scott Van Bramer * ,

Department of Chemistry, Widener University, One University Place, Chester, Pennsylvania 19013, United States

Katherine R. Goodrich

Department of Biology, Widener University, One University Place, Chester, Pennsylvania 19013, United States

J. Chem. Educ., 2015, 92 (5), pp 916–919

DOI: 10.1021/ed5006807

Publication Date (Web): January 30, 2015

Copyright © 2015 The American Chemical Society and Division of Chemical Education, Inc.

Supporting Documents (9 pages): Student Instructions Handout detailing the experimental steps and post-lab questions and activities; experimental modifications, background information on mass spectroscopy and SPME, grading rubric for notebook, report, and presentation.

ABSTRACT: http://pubs.acs.org/doi/abs/10.1021/ed5006807

This paper describes an SPME/GC-MS experiment that might be suitable for introducing Chemistry students to chemical aspects of plant biology or providing biology students a taste of analytical chemistry.  The authors describe the extraction, characterization, and analysis of volatile chemicals from plants.

SPME involves the use of a silica fiber coated with a GC column stationary phase.  The fiber is exposed to the plant extract solution or head space to let the chemical components adsorb on the surface.  The fiber is then inserted into the injection port of the GC where the hot temperature volatilizes the chemical mixture.  The mixture is separated into its components as it travels through the GC column. Each component can then be identified using MS analysis.

Use of SPME in both laboratory teaching setting and research is well-documented.

Flowers and vegetative tissue emit volatile molecules sometimes when wounded.  These volatile compounds can function to “attract or deter other organisms in the environment such as insect pollinators or herbivores”.

The volatile components can be collected by wrapping low-volatile plastic bags around live plant tissue.  The SPME fiber can be inserted inside the bag to collect sample.

Some expected chemicals that are amenable to MS analysis include terpenoids, aliphatics, and benzenoids.  Linalool and ocimene can also be expected from a broad selection of plants.

The experiment described was done as a 3-hour lab in an Instrumental Analysis class for chemistry majors.

EXPERIMENT

Some procedural notes below:

·         Students collected plant samples (flowers or vegetation) from the campus.  Fresh sample have to be run because the volatile compound profile changes over time as plant tissue senesces and dies.

·         Experimental conditions for sample collection, fiber loading, and GC-MS analysis were cited in the reference. (See student instruction sheets in the supporting document for procedure.)

·         The cut samples were sealed in low volatile oven bags for about 15 minutes.  The SPME fiber was inserted and exposed to the accumulated gas for 15 minutes.

·         An HP GC-MS was used in the experiments; the GC-MS parameters are provided in the supporting information.

·         As a post-lab activity, students were asked to select several compounds identified in the analysis and do literature research and presentation on it.

HAZARDS

None noted.

RESULTS

·         Table 1 in the paper lists the most common compounds identified in the analysis: monoterpenes, sesquiterpenes, aliphatic compounds, and benzenoid compounds.  Biosynthesis of these compounds are well-documented.

DISCUSSION

·         Sample components were characterized by 5 or more large chromatogram peaks and many other smaller peaks.

·         Coordination between sample prep and scheduling of GC-MS use to run analysis on fresh samples was a logistics challenge even though the class only had 7 students.

·         Another significant challenge was acquiring good NIST library matches. In many cases, this required students carrying out background subtractions, signal averaging, and extracted ion chromatograms to get a clean mass spectrum for matching.

·         The culminating student presentations included information on sampling methodology, GC-MS data analyses, compound identification, and background information.  Students were surprised to see that some of the compounds they identified from their sample showed up in other students’ samples as well.

CONCLUSIONS

·         Some suggestions for modifications are given (can also be found in the supporting documents).