Photostability of morphine and 6-MAM exposed to controlled UVB/UVA irradiation in water and methanol solution. Comparison with data in the solid state

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 not only in clinical and forensic toxicology to investigate people drug use and abuse, but also in analyses of waters, especially in surface waters and sewage treatment plants, as they are new emerging environmental pollutants. Moreover, the quantification of these particular drugs and metabolites is of interest in the so called “sewage epidemiology”, a novel approach for estimating drug consumption in a community by wastewater analysis. The UVA and UVB light sensitivity of 6-monoacetylmorphine (6-MAM) and morphine, the main metabolites of heroin, has been studied in methanol, water 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. The photodegradation appears to be slightly faster for Morphine at lower doses. The photolysis rates in water are nearly one third lower than in methanol. In the solid state, the yield of photodegradation is lower than in solution. 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 and the same photoproducts due to oxidative process were identified in solution and the solid state.