Detection and quantification of metastable photoproducts of trenbolone and altrenogest using liquid chromatography-tandem mass spectrometry.

•Unstable photoproducts of trenbolone and altrenogest were quantified via LC–MS/MS.•Photoproducts were generated onsite with solar simulator.•Cold, neutral conditions, fast processing, and [M + Na]+ control improve performance.•SPE extracts of photoproducts are stable for up to a month.•Sample acidification can be used to quantify photoproducts indirectly.