Contactless hair decontamination: Ionic liquids remove opiates
Cleaning hair for drug analysis
Opiates have been removed from the surface of human hair by a contactless procedure involving ionic liquids, allowing efficient decontamination before analysis of drugs within the hair matrix.
In the world of forensic toxicology, hair has become accepted as a matrix for studying the history of drug taking of an individual due to the stability of drug compounds once they have been deposited. They are taken up at the hair root and maintain their position and concentration in the hair as it grows, so that the length of a hair traps the drug taking pattern. With an average growth rate of 1 cm per month, a long hair can reveal an extensive history.
The technique has become viable in checking compliance in drug treatment programs, workplace testing, and in determining drug use in post-mortem examinations when other tissues are not viable. Although relatively straightforward, one factor which must be overcome is the potential skewing of the findings by external contamination on the surface of the hair. This could originate, for example, from smoking or handling drugs and could have legal implications if it is not taken into account.
Usually, a washing sequence is carried out to clean the hair, using solvents like isopropanol and phosphate buffer to remove residues of personal care products as well as drugs from the surface. However, it has been claimed that this technique might change the structure of the hair, making it more porous and easier for drugs within the hair to escape too.
A team of scientists in Portugal has come up with an alternative way to decontaminate the hair which protects the hair matrix. It relies on an ionic liquid, which would dissolve the hair completely if they came into contact. The solution is to prevent direct contact as explained by Mário Barroso and colleagues from the National Institute of Legal Medicine and Forensic Sciences, Lisbon, and the University of Lisbon.
ionic liquids in Y-shaped flask
The hair and the ionic liquid are kept apart by placing them in separate legs of a custom-made inverted Y-shaped glass cell. Upon heating in a GC oven, the surface contaminants were driven from the hair and passed by diffusion to the other leg where they were absorbed in the ionic liquid.
From 40 ionic liquids with different cations and anions, three were found to be particularly effective and one, 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate, had a decontamination efficiency of more than 90% and was chosen for further study and optimisation.
The researchers did not have any hair from drug users, but produced their own samples by soaking clean hair in solutions of morphine and its metabolite 6-monoacetylmorphine. Self-styled positive samples were made by soaking a concentrated solution for two days whereas the externally contaminated ones were prepared from a dilute solution over one hour.
A design-of-experiments method was used to establish the best conditions for decontamination, varying the temperature of the GC oven, the extraction time, the amount of ionic liquid and the proportion of water in the ionic liquid.
Contact not required
The optimised procedure was compared with a published method that complies with the requirements of the Society for Hair Testing, following the isopropanol-phosphate buffer route. GC/MS under selected ion monitoring mode was used to assess the decontamination in digested hair samples.
The results from the new and established methods were in agreement, indicating that the ionic liquid procedure performed as well as the direct solvent method. However, it is more advantageous as there is no damage to the matrix of the hair, as confirmed by scanning electron microscopy.
In addition, it involves fewer steps than the established method and is completed within 16 hours. This might seem a long time but it can be multiplexed by adding several of the Y-cells to the oven at once where they can be decontaminated overnight. And once the loaded cells have been placed in the oven, there is no operator intervention.
The next stage will be to confirm that the method is as effective with real hair samples containing opiates, before looking to see whether it can be applied to other compounds of low volatility in different areas of application.
Related Links
Drug Testing and Analysis 2014 (Article in Press): "Development, optimization, and validation of a novel extraction procedure for the removal of opiates from human hair's surface"
