In his dissertation, Scherer reported four specific hydrocarbons present in significant amounts in every head louse sample he studied. These four hydrocarbons represent approximately 50% of the cuticle hydrocarbons of head lice, and had retention time indices (RI) of 2500, 2700, 2900 and 3075.
The peaks that corresponded to the four retention time indices attributed to the head louse by Scherer were integrated and compared qualitatively to the alkane standard.
The alkane calibration mixture, when run by GC, produced a chromatogram with regular peaks correlating with each respective component. The retention time indices for the four specific hydrocarbons of interest were 2500, 2700, 2900 and 3075.
The baseline experiment, comparing the chromatogram of the scaled-up iso-octane extraction (10 lice in 80 μL iso-octane) correlated very well with the analogous chromatogram published by Scherer. As expected, the main peaks observed for this sample had retention time indices of 2500, 2700, 2900 and 3075.
In a control experiment, 10 head lice were co-extracted by immersion with 50/50 methanol: water. This 50/50 methanol: water solution was found visually to provide entire wetting of the head louse. However, the chromatogram produced from the analysis of the aqueous methanol extract showed a complete lack of CHC removal efficiency.
As seen in the gas chromatogram overlay (Figure 1), Isopropyl myristate/cyclomethicone D5 (IPM/D5) had equivalent efficacy extracting the four target hydrocarbons from the lice cuticular wax as iso-octane. The IPM/D5 (isopropyl myristate/cyclomethicone D5) (red) chromatogram is artificially shifted to the right, offset for visualization purposes, because the four peaks of interest were virtually identical in peak shape and height to those in the iso-octane chromatogram.
Gas Chromatogram demonstrating head lice epicuticle hydrocarbon extraction efficiency of isopropyl myristate/cyclomethicone D5 vs. iso-octane (offset for visualization purposes).
BMC Dermatol. 2012;12(15) © 2012 BioMed Central, Ltd.