An evaluation of two wash procedures for the differentiation of external contamination versus ingestion in the analysis of human hair samples for cocaine.

In order to evaluate the effectiveness of a wash procedure using isopropanol followed by multiple extended phosphate buffer washes as compared with a methanol wash procedure previously reported, a contamination experiment was designed involving the soaking of human head hair in cocaine-contaminated aqueous solutions. Fourteen negative human head hair samples were soaked in a solution of cocaine HCl (1000 ng/mL) at room temperature for 1 h, then rinsed with distilled water and dried at room temperature. Using the extensive wash procedures (15-min isopropanol wash, followed by three 30-min phosphate buffer washes and then two 60-min washes), in no case would any of the samples be reported out as positive at a cut-off of 5 ng cocaine/ 10 mg hair. With the methanol procedure, 8 of the 14 methanol-washed samples exceeded a cut-off of 5 ng/10 mg hair. Extensive washing was shown to be far more effective for removal of external contamination than the methanol wash procedure reported. In all cases, the extensive aqueous wash protocol would allow the differentiation of ingestion versus external contamination, as defined by this soaking experiment. All samples underwent solid-phase extraction and derivatization followed by liquid chromatographic-tandem mass spectrometric analysis. Analysis was performed on a triple quadrupole API 2000 PerkinElmer Sciex mass spectrometer (MS) equipped with an atmospheric pressure ionization source via an ion spray interface. The MS operated in the positive Cl multiple reaction mode.