Photodegradation of 6-monoacetylmorphine and morphine in solution and in the solid state under controlled UVB/UVA light

In the last years, many analytical methods based on liquid chromatography coupled with mass spectrometry detection have been developed to identify drugs of abuse and their metabolites. These studies are performed both in clinical and forensic toxicology, to investigate people drug use and abuse, and in analyses of waters, especially in surface waters and sewage treatment plants, as they are new emerging environmental pollutants. The UVA and UVB light sensitivity of 6-monoacetylmorphine (6-MAM) and morphine, the main metabolites of heroin, has been studied in methanol, aqueous solution and in the solid state by Liquid Chromatography - High Resolution, high accuracy Mass Spectrometry (LC-HRMS). The extent of photolysis in methanol/water solution and in the solid state was also calculated by LC HRMS analysis. The two analytes are quite stable under UVA light but very sensitive to UVB irradiation. In particular, they revealed to undergo a similar photodegradation pattern, both reaching 90% after 100 J/cm2 of UVB irradiation in methanol. At lower doses (20 and 40 J/cm2), photodegradation in solution appears to be slightly faster for morphine than 6-MAM. In general, the photolysis rates in water are nearly one third lower than in methanol. In the solid state, the yield of photodegradation is much lower than in solution (i.e., for 6-MAM, 1% and 2.5% decomposition after 100 and 300 J/cm2 of UVB , respectively) but sufficient to identify some new products formed. The description of possible structures of photoproducts obtained under UVB irradiation is presented. Photoaddition of the solvent and photooxidation seem to be the main pathways of phototransformation of these molecules under the above experimental conditions.