John V. Goodpaster, Byron C. Drumheller, and Bruce A. Benner, Jr.
Analytical Chemistry Division, Chemical Sciences and Technology Laboratory
Currently, methods for the forensic analysis of human hair rely upon
microscopic examination or DNA comparisons. Chemical techniques, on the
other hand, have largely focussed on extracting and identifying drugs of
abuse. Recent work in our laboratory has shown that organic material on
the surface of hair is easily accessible using conventional extraction
techniques and solvents, readily analyzed using gas chromatography/mass
spectrometry (GC/MS), and provides qualitative and quantitative information
that may be effective for forensic identifications or comparisons. In this
work, various extraction methods such as ultrasound, Soxhlet, pressurized
solvent, and supercritical fluid extraction have been evaluated for their
efficiency and selectivity. Using these procedures, the organic fraction
of the surface of hair was extracted by methanol, acetone, dichloromethane,
hexane, and supercritical carbon dioxide. Yields from hair samples were
0.9% - 1.8% (mass fraction) for ultrasonic extraction, 1.1% - 4.1% for
Soxhlet extraction, 2.5% - 3.6% for pressurized solvent extraction, and
2.4% for supercritical fluid extraction. Of the liquid solvent extraction
techniques, pressurized fluid extraction was the most convenient and amenable
to samples as small as 50 mg. In general, yields for all techniques decreased
as solvent polarity decreased. Characterization of the hair extracts revealed
a complex mixture of components ranging in carbon number from C14 to C33.
This material consists of sebaceous excretions such as fatty alcohols,
acids, esters, other lipids including squalene and cholesterol, and anthropogenic
material from consumer products. Despite its lower extraction efficiency
compared to the liquid solvents, supercritical fluid extraction has been
the most successful method to date for very small hair samples. SFE has
been applied as an on-line method using both static and dynamic modes.
The pressure, temperature, and time of extraction have been optimized in
order to maximize sensitivity and samples as small as 100 ug have been
successfully analyzed. A restrictor is used to deposit the solutes directly
onto the stationary phase of the chromatographic column. Subsequent chromatographic
analysis time is on the order of 60 min. Analysis of head hair from 20
subjects varying in age and gender has shown that these chromatograms are
suitably complex to provide some degree of individualization to a particular
hair sample. Furthermore, there appears to be systematically higher levels
of cholesterol in pre-pubescent versus post-pubescent individuals. Literature
data suggest that further systematic differences in lipid composition according
to gender and/or race may exist that would further increase the evidentiary
value of chemical analysis. Finally, the chromatographic profiles obtained
using this technique have proven to be stable under normal storage conditions
and are reproducible for a single scalp location on an individual. Future
work will include correlating the results with demographic data from subjects.
An expanded sampling study is also needed to determine the amount of variation
in the chromatographic profile of a single individual over time and scalp
location. Lastly, chemometric pattern recognition algorithms will be used
to quantitatively compare chromatographic profiles.