Evaluation of decontamination procedures for drug testing in undamaged versus damaged hair

Abstract

Although substances incorporated by ingestion are strongly bound to hair, their loss may occur if aggressive decontamination procedures are applied, especially in highly damaged/porous hair. Evaluation of cleaning procedures using hair samples with different porosity obtained from ethanol or drug users (cocaine, heroin, methamphetamine, methadone, fentanyl, tramadol, diazepam, buprenorphine, dihydrocodeine, citalopram and trazodone). The effect of washing time and multiple wash steps with water and methanol were evaluated. Hair samples (n = 16) were selected and evaluated according to (a) the drug pattern consumption, (b) available amount, and (c) hair porosity (c1 ‘cosmetic treatment’, c2: storage time). Six of them were soaked with an aqueous deuterated analogue solution. The samples were cut in 1‐cm segments and homogenized. All hair samples were then decontaminated one or six times with 1.5 ml of water or methanol during 1, 5, 15, 30, 60 and/or 90 min (n = 1 to 3/sample, depending on the available amount of hair). Hair extracts were then cleaned up via a solid‐phase extraction (SPE) or liquid–liquid extraction (LLE), while the washes were evaporated to dryness. All were thereafter reconstituted and analysed with routine ultra‐performance liquid chromatography–tandem mass spectrometry (UPLC‐MS/MS) methods. Although concentrations of parent drugs and/or metabolites presented a negative trend along the washing time with methanol (up to 80%), the compounds were relatively well retained in hair even after a 90 min wash (with methanol or water) in most samples, and their retention would depend mostly on the hair nature rather than their physicochemical properties (whether incorporated by ingestion and/or from external contamination). Moreover, parent drugs and/or metabolites were detected in the washes in most samples, and the ratio between hair and washes decreased along the washing time. More than 50% of the deuterated analogues soaked into hair were still present after the different washing steps. Losses were observed more frequently for long‐term stored hair samples, after decontamination with methanol for more than 30 min. Therefore, prolonged or repeated cleaning with methanol should be avoided in general procedures.