Forensic analysis of hair surface components using off-line supercritical fluid extraction and large volume injection

The analysis of organic material on the surface of human hair may indicate various subject characteristics such as age, race, gender, or the use of hair products. In addition, comparisons of hair chemical composition may be used to assess the potential for a common origin between a known and unknown sample. However, evidentiary hair samples are often extremely small, necessitating highly sensitive extraction and analysis techniques. In this communication, off-line supercritical fluid extraction (SFE) followed by gas chromatography/mass spectrometry (GC/MS) using large volume injection (LVI) is demonstrated as a potential method for extracting and analyzing hair surface components. The retention gap technique was used to achieve large volume injections, allowing up to 30 μL of the off-line extracts to be analyzed. Subsequent chemical analysis by GC/MS identified various natural components on the hair surface such as saturated and unsaturated free fatty acids, squalene, and cholesterol. Overall, off-line SFE was quite efficient, allowing the measurement of surface components of sample amounts ranging from 0.22 mg to 0.24 mg. In addition, derivatization of free fatty acids using a silylating agent increased both chromatographic resolution and sensitivity. Results from two hair samples are discussed to demonstrate the technique.