A study on photodegradation of methadone, EDDP, and other drugs of abuse in hair exposed to controlled UVB radiation.

The drug content of hair may be affected by washing, chemical or thermal treatments, the use of cosmetics, or exposure to the environment. Knowledge concerning the effect of natural or artificial light on drug content in hair can be helpful to the forensic toxicologist, in particular when investigating drug concentrations above or below pre-determined cut-offs. The photodegradation of methadone and its metabolite, 2-ethyl-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) was studied in authentic positive hair samples by comparing drug concentrations determined by liquid chromatrography-high resolution mass spectrometry before and after exposure to UVB light (in vivo study). The same approach was applied in order to investigate the light sensitivity of opiates (6-monoacetylmorphine and morphine) and cocainics (cocaine and benzoylecgonine) in true positive hair. The yields of photodegradation were calculated for each drug class in eight different positive hair samples irradiated by UVB at 300 J/cm(2) obtaining averages, ranges and standard deviations. In parallel, the photostability of all the compounds as 10(-5) -10(-4)  M standard solutions in methanol were examined by means of UVB light irradiation in the range 0-100 J/cm(2) followed by UV/Vis spectroscopic analysis and direct infusion electrospray ionization-high resolution mass spectrometry (in vitro study). In hair, methadone was shown to be significantly affected by light (photodegradation of 55% on average), while its metabolite EDDP proved to be more photostable (17%). 6-monoacetylmorphine, morphine, benzoylecgonine, and cocaine were more photostable than methadone in vivo (on average, 21%, 17%, 20%, and 11% of degradation, respectively). When irradiated in standard solutions, the target molecules exhibited a larger photodegradation than in vivo with the exception of cocaine (photodegradation for methadone up to 70%, 6-monoacetylmorphine and morphine up to 90%, benzoylecgonine up to 67%, cocaine up to 15%). Some factors possibly affecting the yields of photodegradation in hair and partially explaining the differences observed between the in vivo and the in vitro studies were also investigated, such as the colour of hair (the role of melanin) and the integrity of the keratin matrix.