Amphetamine and N-acetylamphetamine incorporation into hair: An investigation of the potential role of drug basicity in hair color bias

To elucidate the role of drug basicity in the preferential incorporation of certain drugs into dark hair rather than light hair, Long-Evans rats were dosed with amphetamine or its non-basic analogue N-acetylamphetamine (N-AcAp) and their hair evaluated for drug content. Rats were shaved prior to dosing. On the 14th day after dosing, hair from the same area that was shaved prior to dosing was shaved and collected. After the addition of amphetamine-d₃ or N-AcAp-d₃ as an internal standard, hair samples (20 mg) were digested in 1M NaOH at 37°C. Digested solutions were then extracted with n-butyl chloride/chloroform (4:1, v/v). After drying and reconstituting, samples were injected onto a ThermoQuest TSQ liquid chromatography-tandem mass spectrometry instrument for analysis. Black hair from rats dosed with amphetamine (n = 8) was found to contain 6.44 ± 1.31 (SD) ng amphetamine/mg hair. White hair from the same rats contained 2.04 ± 0.58 ng amphetamine/mg hair. In contrast, no difference in N-AcAp content was found between black hair (0.87 ± 0.08 ng N-AcAp/mg hair) and white hair (0.83 ± 0.15 ng N-AcAp/mg hair) from rats dosed with N-AcAp (n = 8).