Abstract
Lipids play an essential role in providing energy and other physiological functions for insects. Therefore, it is important to determine the composition of insect lipids from cuticular and internal tissues for a better understanding of insect biology and physiology. A novel non-derivatization method for the analysis of lipids including fatty acids, hydrocarbon waxes, sterols in Tribolium castaneum (Herbst) and Rhyzopertha dominica (Fabricius) was explored using the direct immersion solid-phase microextraction (DI-SPME) coupled with gas chromatography–mass spectrometry (GC–MS). Nine extraction solvents, acetonitrile, methanol, hexane, ethanol, chloroform, acetonitrile and ethanol (1:1 v/v), acetonitrile and water (1:1 v/v), ethanol and water (1:1 v/v) and acetonitrile and ethanol and water (2:2:1 v/v/v) were selected and evaluated for the extraction of insect lipids with DI-SPME fiber. Acetonitrile extraction offered the best qualitative, quantitative, and number of lipids extracted from insects samples results. Acetonitrile extracted high-boiling point compounds from both species of tested insects. The range of hydrocarbons was C25 (pentacosane) to C32 (dotriacontane) for T. castaneum and C26 (11-methylpentacosane) to C34 (tetratriacontane) for R. dominica. The major compounds extracted from the cuticular surface of T. castaneum were 11-methylheptacosane (20.71%) and 3-methylheptacosane (12.37%), and from R. dominica were 10-methyldotriacontane (14.0%), and 15-methyltritriacontane (9.93%). The limit of detection (LOD) for the n-alkane compounds ranged between 0.08 (nonacosane) and 0.26 (dotriacontane) µg/g and for the fatty acids between 0.65 (arachidic acid) to 0.89 (oleic acid) µg/g. The study indicated that DI-SPME GC–MS is a highly efficient extraction and a sensitive analytical method for the determination of non-derivatized insect lipids in cuticular and homogenized body tissues.
Highlights
Lipids are the main biological compounds in animals and plants [1], including fatty acids and hydrocarbon waxes on and in insect bodies [2]
Since fiber coating was reported as a vital factor in the development of an appropriate Solid-phase microextraction (SPME)
The selection was based on previous research [25,26] and because the fiber coating of DVB/CAR/PDMS covers wide range of polarities from non-polar to polar compounds, which enables it to extract a wide range of compounds; as such, the extraction was strongly affected by the polarity of the SPME [24]
Summary
Lipids are the main biological compounds in animals and plants [1], including fatty acids and hydrocarbon waxes on and in insect bodies [2]. Fatty acids are the most basic form of biological lipids. The cuticular lipid layer of the insect consists of different chemicals such as a long chain of hydrocarbons and fatty acids [4]. An analysis of the cuticular lipids of Acanthoscelides obtectus showed that adults contain a variety of chemicals such as hydrocarbons, triacylglycerols, fatty acid esters, free fatty acids, sterols, aldehydes, ketones and alcohols [5]. An analysis of cuticular lipids from adults of Zygogramma exclamationis showed that large amounts of lipids in the cuticle of males and females were hydrocarbons ranging from C23 (tricosene) to C56 (trimethyltripentacontane) [7]
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