Binding of drugs to hair and their correlation to amino acid concentration

Urinalysis is the most widely used method for drug testing. It yields, however, few positive results because drugs only remain in the urine for up to six days. In contrast, hair testing is becoming more widely used because drugs can remain in the hair for three to six months. In addition, hair analysis, which may provide more positive results, is less invasive. A problem with hair analysis is that various hair types will yield different concentrations resulting from exposure to illicit drugs such as cocaine, heroin, and amphetamines, which leads to fairness issues. To test the hypothesis that drug uptake varies, various hair types were washed and exposed to drugs and rewashed. Twenty milligrams of hair were pulverized, extracted twice with 0.1M HCl, derivatized, and analyzed by GC/MS. Hair that was cosmetically treated displayed the highest concentration of drug. Cosmetically treated hair is negatively charged. Drugs are positively charged at pH 7.0; physiological pH is 7.3. In conclusion, drugs tended to bind more readily to negatively charged hair.