Study of drug distribution in hair by infrared microscopy visualization

Infrared microscopy has been shown to be a unique method of analysis for drugs-of-abuse determinations in hair, with the ability to analyze only the central core, or medulla region, of sectioned hair. By spectrally mapping infrared functional groups related to the various drugs, a three-dimensional image of the drug location can be obtained from cross-sectional and laterally microtomed hairs. This technique eliminates the question of externally contaminated hair by analyzing only that portion of the hair that is formed from within the root where ingested material would be transported. Results from these tests have shown a direct correlation between drug and medulla presence in the hair. There are occasional occurrences of drug in nonmedullated hair, but the drug distribution across the hair is entirely different in these cases. Spiked or doped hair has been shown to be the exact opposite of drug-ingested hair; the drugs spike into the hair better in nonmedullated portions. From these mapped images, two routes of drug incorporation into the hair can be postulated. The more prominent would be through the root, where the hair shaft is formed, with the drug binding to the medulla material. A second less prevalent route would be from the exterior through the cuticle via perspiration, as in spiking. The spectral data have also shown that different drugs bind differently to the various hair materials.