Gas chromatography-mass spectrometry and Raman imaging measurement of squalene content and distribution in human hair

A sensitive and specific gas chromatography-mass spectrometry (GC-MS) method was developed and validated for the measurement of the squalene content from root to tip, in both Chinese black virgin and bleached hair. Deuterated squalene was used as the internal standard. For quantification, selective ion monitoring (SIM) at m/z 410.0 and 347.0 were monitored for squalene and deuterated squalene, respectively. Different methods for the extraction of squalene from ex vivo human hair were compared including organic solvent extraction and acid/alkali hydrolysis. The best extraction efficiency was obtained by using a mixed solvent consisting of chloroform:methanol = 2:1 (v:v). The linear range of squalene ran from 1.0 to 50.0 μg mL⁻¹. The limit of detection (LOD) was 0.10 μg mL⁻¹ (corresponding to 0.005 mg g⁻¹ in human hair), which enabled quantification of squalene in human hair at very low level. The recovery of squalene was 96.4 ± 1.46 % (n = 3). Using the above-mentioned mixed solvent extraction, squalene content in human hair was successfully quantified from root to tip. Meanwhile, a Raman imaging method was developed to visualize the squalene distribution in Chinese white virgin hair from cuticle to medulla.