|Bernier, Ulrich - Uli|
Submitted to: American Society for Mass Spectrometry
Publication Type: Abstract only
Publication Acceptance Date: 5/28/2006
Publication Date: N/A
Citation: Interpretive Summary: None.
Technical Abstract: Introduction: Natural repellents that are alternatives to synthetics are commonly sought but few provide adequate protection from blood-feeding mosquitoes and biting flies. It is known that arthropods are selective in choice of host, e.g. ornithophilic mosquitoes will heavily target avians over humans for a bloodmeal. Additionally, there may be host-produced compounds that deter these arhtropods from blood-feeding. Prior studies have shown giraffes to be less preferred hosts of tsetse flies and volatiles from the pelage extracts were found to contain compounds known to repel mosquitoes and ticks. Method: Approximately 2 g of male giraffe pelage hair and wax were collected in three separate vials for subsequent sample preparation and GC/MS analysis. A different solvent (10 mL hexane or dichloromethane) was added to each vial, prior to injection of 1 µL of this solution onto a ThermoQuest Trace GC/MS with a 30 m DB-WAXetr column (0.25 mm i.d., 0.25 µm film thickness) operated in EI mode. The sample in the third vial was transferred to a Tedlar bag, sealed, purged with nitrogen and sampled by headspace concentration with an Entech 7001A and analyzed on a ThermoQuest DSQ GC/MS equipped with a Restek 60 m DB-1column (0.32 mm i.d., 1 µm film thickness). Preliminary Data: Wood and Weldon  have identified the major volatile constituents of giraffe pelage as nonanal, 3-methylindole, hexadecanoic acid, 3,5-androstadien-17-one, and tetradecanoic acid. The GC/MS analysis of solvent-based samples indicates that cholesterol is one of the major constituents. The next most intense peak has been identified tentatively as prasterone-3-sulfate. This compound is a metabolite of dehydroepiandosterone, a weak androgen, and in humans is produced in the adrenal glands. The other major less volatile constituents appear to be primarily hydroxylated methyl esters of hexadecanoic and octadecanoic acids and hexadecanoic acid. In the more volatile region, a significant amount of 3-methylindole and p-cresol are observable, along with a series of substituted pyrazines, heptanal, 2-heptanone, and nonanal. Although there appears to be low levels of aldehydes in the series from pentadecanal to octadecanal, tridecanal was present in a surprisingly high amount. In addition, 2-tridecanone is also present at higher than expected levels. With the exception of nonanal and the aldehydes mentioned above, it is likely that other aldehydes may be present, but are below our limit of detection. The analysis of the headspace above giraffe pelage hair and wax when analyzed by microscale purge and trap GC/MS indicates that the most abundant volatiles are all ketones: 2-butanone, 4-methyl-2-pentanone, methyl isobutyl ketone, 3-methyl-2-butanone, 2-pentanone, 3-methyl-2-pentanone and 4-methyl-3-penten-2-one. Heptanal and 2-heptanone are also observed by this method; however, they are present at much lower abundances than seen in the solvent injection. This is thought to result from imparted bias against the larger polar molecules when using microscale purge and trap.