Date of Award

Spring 5-2023

Document Type


Degree Name

Master of Science (MS)


Forensic Science



First Advisor or Mentor

Ana Pego

Second Reader

Marta Concheiro-Guisan

Third Advisor

Sarah Carobini Werner de Souza Eller Franco de Oliveira


Hair external contamination is a challenging phenomenon that may compromise hair testing interpretation. Previous research has found that cosmetic hair treatments can decrease concentrations of drugs that are already present in the hair shaft, however little is known about the impact of these treatments on the hair when the drugs are deposited externally. The aims of the present study were to explore how henna and bleach treatments influence cocaine external contamination. Sixteen authentic hair samples were collected from volunteers with varying hair colors and shapes and were confirmed negative for cocaine and benzoylecgonine by a fully validated LC-MS/MS method. Each hair sample was split into three groups: Group A received a cosmetic treatment followed by cocaine and benzoylecgonine contamination; Group B was contaminated first, followed by a cosmetic treatment; and Group C received contamination only. In-vitro contamination involved immersing the samples in a 1 µg/mL COC/BE solution in water for 24 h, followed by overnight drying. Hair samples were washed, extracted, filtered, and analyzed via reversed-phase LC-MS/MS. For hair that was cosmetically treated after cocaine contamination, bleach and henna caused an average decrease in cocaine concentration of 84% (n=15) and 59% (n=13), respectively. For hair that was contaminated after being cosmetically treated, bleach and henna caused an average decrease in cocaine uptake of 52% (n=15) and 92% (n=13), respectively. These results demonstrate that cosmetic treatments influence drug concentrations by removing cocaine that is already present on the hair, as well as by preventing cocaine uptake by the hair.



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