Effect Of Different Headspace Methods On Determination Of Plant Volatiles

Volatile organic compounds released from plants are those whose molecular weights are between 100 to 200,such as hydrocarbons,alcohols,ketones,acids, nitrogen-containing compounds and organic sulfur. These compounds have the higher chemical activity, which plays an important role as messager between plants and plants,plants and the environment or insects. Therefore,qualitative and quantitative study of plant volatiles is the premise for chemical ecology. In the course of the study,it was found that using different sampling methods would make different kinds of volatiles,even the relative content would not remain the same. This caused great uncertainty about qualitative and quantitative analysis of plant volatiles,seriously affecting the reliability of the test.In order to improve the accuracy and precision of the test,in the experiment we compared the properties of five adsorbents(Porapak-Q,Tenax-GR,Tenax-TA,GDX-102 and GDX-101),elution capabilities of four solvents(n-Hexane, dichloromethane, Carbon tetrachloride and Petroleum) and three collection and analysis methods of adsorption-thermal desorption,adsorption-solvent desorption and SPME in the reseach.The aim ischoosing a reliable method for volatiles collection and analysis.The results showed that the capability order of mixed terpene samples going through 5 adsorbents is:Porapak-Q>Tenax-GR,Tenax-TA>GDX-102>GDX-101.The capability of 2 adsorbents made in China was significantly lower than that of importadsorbents. Hexane,Dichloromethane,Carbon tetrachloride and Petroleum were used to elute terpenes absorbed by Porapak-Q. The mixed solvent of Petroleum was the best solvent for elutioning terpenoids. The second and third went to the Hexane and the Dichloromethane,the Carbon Tetrachloride was the last. After one time of desorption ,it is the remaining of a-Pinene,p-Pinene,a-Terpinene,Myrcene,Limonene,Phellandrene, 3-Carene,Caryophyllene that were held in each of the 5 sorbents. Judging From the remainder of the materials,sorbents with thermal desorption results from good to bad was that:Tenax-TA>Tenax-GR>GDX-102>GDX-101>Porapak-Q.The collection and analysis of terpenes standards and volatiles from 3 conifers using above 3 methods indicated that adsorption-solvent elution was the best option for quantitative analysis of terpenoids,and SPME was best for the qualitative analysis. Because of shorter sampling time, Adsorption-thermal desorption is more appropriate for determinating the temporal changes of plant volatiles.