Freeze-thaw method improves the detection of volatile compounds in insects using Headspace Solid-Phase Microextraction (HS-SPME)

Authors: Chen, Jian

Submitted to: Analytical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2017
Publication Date: 7/17/2017
Publication URL: http://handle.nal.usda.gov/10113/5789033
Citation: Chen, J. 2017. Freeze-thaw method improves the detection of volatile compounds in insects using Headspace Solid-Phase Microextraction (HS-SPME). Analytical Chemistry. 89(16):8366-8371.

Interpretive Summary: Gas chromatography coupled with mass spectrometry (GC-MS) is a powerful tool for the identification of volatiles from insects, such as insect pheromones. Sample preparation is an important part of GC-MS analysis, aiming to improve detectability of the analytes. Classical sample preparation methods for insect pheromone analysis involve solvent extraction of insects, which often requires a great number of tested insects and huge volume of solvent. In the past two decades, one technique has been getting more and more popular in insect pheromone analysis is the headspace solid-phase microextraction (HS-SPME). In HS-SPME, the overall amount of volatiles that can be collected for chemical analysis is proportioned to the concentration of volatiles in head space that is largely determined by amount of volatiles insects indeed release into the head space. In many cases, active insect volatiles, such as insect pheromones, are produced in very low quantities. Any practices that can facilitate the release of volatiles into the headspace will facilitate the detection and identification of the volatiles. An innovative sample preparation method for HS-SPME was developed by an ARS scientist, which significantly improves the detection and analysis of insect volatiles. In this method, a freeze-thaw process was applied to insect samples before the conventional SPME extraction. The application of this innovation may significantly facilitate the identification of insect semiochemicals, such as insect pheromones.

Technical Abstract: Headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography–mass spectrometry (GC-MS) is commonly used in analyzing insect volatiles. In order to improve the detection of volatiles in insects, a freeze-thaw method was applied to insect samples before the HS-SPME-GC-MS analysis. Insect samples were first frozen at -80 °C for 10 min and then thawed at 25 °C for 5 min before SPME extraction was performed. The freeze-thaw method clearly improved the detection of volatile compounds for all six tested insect species, including red imported fire ants, Solenopsis invicta Buren, black imported fire ants, Solenopsis richteri Forel, little black ants, Monomorium minimum (Buckley), pharaoh ants, Monomorium pharaonis (Linnaeus); eastern subterranean termites, Reticulitermes flavipes (Kollar); and spotted lady beetles, Coleomegilla maculate De Geer. This method helped identify various volatile compounds in the tested insects, which have never been reported previously. This improved method may facilitate the identification of insect derived volatiles, such as insect semiochemicals.