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Hair analysis is becoming more common in forensics, especially in cases where investigators want to know if drugs facilitated a crime, if a child was exposed in utero, or if someone, say, an athlete or employee, needs to be tested for long-term drug use. But current tests make it difficult to determine actual drug consumption. Some drugs can get incorporated into the structure of hair from the bloodstream, while others, such as cocaine, nicotine, and cannabis, can also contaminate hair from the outside.

Washing the hair sample before analyzing it for drugs has become a standard procedure in an effort to remove external contaminants, although the methods vary and there is the risk that the procedure could actually incorporate contaminants into the hair. In a newly developed technique, published in February in Analytical Chemistry, researchers report being able to completely decontaminate both the outside and internal structure of hairs from people who had taken a particular drug, while leaving evidence of the drug that had come from the bloodstream intact.

In blood or urine, drugs persist for a much shorter time and you cannot necessarily detect their use in the distant past. With hair, you can see a months-long record of drug exposure, depending on the rate of growth, says clinical pharmacologist and toxicologist Gideon Koren of Maccabi Health Services who is not involved with the study.

The aim of the study was to describe a series of methods and tools that can help hair analysis experts better understand how drugs are incorporated into the hair structure and the extent to which hair washing methods can remove external contamination, say coauthors Thomas Kraemer and Markus Baumgartner in an email to The Scientist.

They obtained human hair samples from volunteers who consumed the drug zolpidem (Ambien), a sedative that has been implicated in some crimes. They also received hair samples from people who didn’t take the drug and from those who took one dose of zolpidem at least one month before sampling. Zolpidem is taken orally and typically does not contaminate hair from the outside. To test for external contamination, the team soaked hair samples from people who did not take zolpidem in a solution containing the drug to represent external exposure. The team also split individual hairs longitudinally using specialized equipment and analyzed the strips using laser mass spectrometry to measure the amount of drug present on the outside and inside of the hair. The mass spectrometry results showed that soaking the hairs in the drug solution did contaminate both the outside and inside of the hairs.

The researchers tested several methods for decontaminating hair that have been previously published and one they developed themselves. Among them, only the authors’ protocol was able to completely decontaminate zolpidem-soaked hairs from the outside and inside of hairs, and their method did not remove the drug from the inside of hairs when it had been incorporated from the bloodstream. The authors’ method uses methanol to clean the hair of drugs and has a step that takes 18 hours, which makes it less practical for routine hair analysis. The results suggest that other hair washing methods are less effective for decontaminating hair from external exposure.

Combining the washed hair samples with the mass spectrometry analysis, “it’s an important method to understand what comes from the outside and what grows from the inside,” says Koren.

“This is an academic, very well written paper by a high reputation team,” says toxicologist Pascal Kintz of X-Pertise Consulting who is not involved with the study, in an email to The Scientist. “However, it has little interest for routine applications, due to the complexity of the technology which was used.”

The authors acknowledge the limitations of the techniques as far as real-world applications go. “We always state in our presentations that the special and laborious techniques we are using to elucidate mechanisms of how drugs finally reach the inside of a hair or how they finally can be extracted from the hair are usually not suitable for routine hair analysis,” say Kraemer and Baumgartner.

Although the practical use for this study’s methods may be limited, Koren says that the largest contributions of this study are to show that you can visualize where drugs build up in the hair using mass spectrometry and to investigate the basic science of when drugs are incorporated from the body and bloodstream in comparison to external sources.

Because zolpidem does not typically contaminate hairs from the outside, “much more research will be needed for other medications,” Koren tells The Scientist. The authors tell The Scientist that they have begun running experiments to test their hair washing method on cocaine and other drugs to see if the methods are as successful in removing external contamination, “but it will take some time until we have final results.”