Insights into the Decontamination of Cocaine-Positive Hair Samples

Abstract

A highly discussed step in hair sample preparation for forensic analytics is the applied decontamination. The here presented investigations aim to gain insight and give recommendations on how to conduct this decontamination for the analysis of cocaine consumption in hair. Key insights were gained from the investigation of cocaine consumer hair, which was artificially contaminated in a humid atmosphere with 13C6 labelled cocaine and from cocaine powder contaminated hair. Several decontamination protocols were investigated, whereby the usage of a decontamination protocol consisting of multiple short repetitive washes allowed to visualize the wash-out of (13C6-) cocaine. Multiple methanol washes proved to be an efficient and simple decontamination approach. Our findings showed that decontamination protocols can successfully wash-out recent cocaine contaminations. They were observed to be rather quickly washed-out. Whereas cocaine from consumption or “older” cocaine contaminations were shown to eliminate both at a constant rate (from inner hair compartments). Thus, the usage of decontamination protocols to differentiate between consumption and contamination was shown to be limited. As contamination can happen any time at any level, only the application of elaborated decision trees, based on cocaine metabolite ratios and thresholds, can provide the distinction between consumption and contamination. Thus, the authors highly recommend the usage of such tools on all hair samples analyzed for cocaine consumption.

Identifying contamination versus ingestion in hair testing, with cocaine as example

“…With intacthair, the drug that has been deposited from the bloodstream while the hair is in the follicle is not removed by water, the fastest and most thorough solvent for swelling hair. Experiments that failed to demonstrate a diffusion‐resistant compartment distinct from contaminating drug did not carry out the diffusion time sufficiently 16–18 or with sufficient maintenance of a diffusion gradient 21 in order to make this determination. Others have failed to have a sufficiently large ratio of solvent:hair to create a strong gradient 19,20 .…”

“…Experiments that failed to demonstrate a diffusion-resistant compartment distinct from contaminating drug did not carry out the diffusion time sufficiently [16][17][18] or with sufficient maintenance of a diffusion gradient 21 in order to make this determination. Others have failed to have a sufficiently large ratio of solvent:hair to create a strong gradient.…”

“…Abundant solvent is required in order to create a concentration gradient between the solvent and hair, bearing in mind that the amount of drug in the hair is not known beforehand and could be very large. Failure to make frequent changes of solvent during the washing procedure also thwarts the goal of optimizing the concentration gradient 21 …”

“…Failure to make frequent changes of solvent during the washing procedure also thwarts the goal of optimizing the concentration gradient. 21 A moderate increase in temperature benefits diffusion, with a warning that temperatures above 40 C, as done by one investigator, 20 may alter some proteins 22 and may also affect compounds that are esters. The presence of albumin (e.g., 0.1%) in an aqueous washing medium provides a competing binding agent 23 to aid in dissociation of the drug from keratin proteins and, along with frequent changes of wash medium, to discourage re-entry of the washed-out drug back into the hair.…”

Tacrolimus monitoring in hair samples of kidney transplant recipients

“…For instance, tenofovir concentrations measured in hair samples can be readily used to monitor treatment adherence in HIV patients ( 23 ). However, although LC-MS/MS analysis of substances in hair is specific and sensitive, certain factors, such as hair products, hair washing routines, hair color, and artificial coloring, are known to significantly affect the results of hair analysis ( 20 , 24 , 25 ).…”