Hair testing is a powerful tool routinely used for the detection of drugs of abuse in toxicology and forensic applications. The analysis of hair is highly advantageous as it can provide prolonged detectability versus that in biological fluids and chronological information about drug intake based on the average growth of hair. However, current methodology routinely involves complex and time-consuming sample preparation followed by gas or liquid chromatography coupled with mass spectrometry. Mass spectrometry imaging has been employed to monitor the distribution of cocaine throughout a single hair sample.

Longitudinal sections of hair samples were accomplished using an in-house built device before mounting onto a conductive glass slide. Prior to analysis samples were gold-coated using a Quorum Technologies SC7640 sputter coater (New Haven, USA) equipped with a FT7607 quartz crystal microbalance stage and FT690 film thickness monitor to deposit a 1 nm thick gold layer. Data was then acquired using a Physical Electronics TRIFT II TOF-SIMS (Physcial Electronics, USA) equipped with an Au liquid metal gun tuned for 22keV Au⁺ primary ions. Data was analysed and visualized using WinCadence software version 4.4.0.17 (Physical Electronics).

Scanning electron microscopy was performed to asses the quality of the longitudinal sections of hair samples. The images obtained from the sectioned hair sample showed the exposed medulla, cortex and a portion of the cuticle observed as a narrow layer surrounding the cortex. Metal assisted-secondary ion mass spectrometry (MetA-SIMS) images of longitudinally sectioned hair samples showed the distribution of endogenous elements such as sodium, potassium and calcium. Analysis of user hair samples showed the distribution of cocaine at m/z 304 and the major fragment at m/z 182 derived from the neutral loss of benzoic acid.

The work reported here presents a device for the preparation of longitudinal sections of hair samples without the use of an embedding medium for analysis by MetA-SIMS. By using high spatial resolution imaging a more precise time-line on drug intake can be obtained.