Hair Analysis for Cocaine: The Requirement for Effective Wash Procedures and Effects of Drug Concentration and Hair Porosity in Contamination and Decontamination

It has been proposed that issues of external contamination of hair can be resolved by the presence of metabolites. This is true for some drugs in some circumstances. However, even if some metabolites such as cocaethylene are sufficiently definitive to indicate certainty of use, others such as benzoylecgonine can occur as contaminants. In addition, for phencyclidine, only the parent compound is determined. Therefore, effective washing procedures are needed to rule out contamination as the source of the parent or metabolite. The protection provided by cutoffs is also dependent on washing to remove surface contamination, which can range from very little to greater than 20 times the amount in the hair. In cocaine-positive head hair samples from 67 subjects with cocaine-positive urine tests, contamination of positive hair samples ranged from 0.7 to 8009 ng/10 mg hair, demonstrating that analyses of such samples to determine use is meaningless without removal of contamination. Wash procedures have been a focus of this laboratory for many years. In this paper, the effectiveness of our wash procedure was further challenged by application to negative hair (blonde, auburn, brown, and black) contaminated by soaking for 1 h in 1000, 10,000, and 50,000 ng cocaine/mL water. The uptake of the cocaine was approximately linear with increasing concentrations of cocaine in the soaking solutions. By application of the wash criterion, all samples were clearly identified as contaminated (i.e., negative). The effects of hair porosity on uptake of cocaine were also studied with 10 hair samples of all colors. Permed and unpermed samples were soaked in 10,000 ng cocaine/mL for 1 hour. All hair responded to the perm with increased uptake, and all were decontaminated or identified as contaminated (i.e., negative for cocaine use). Porosity, not hair color, determined the rate of penetration of hair by cocaine in solution, and, likewise, washing characteristics were unrelated to hair color.