Thermospray high-performance liquid chromatographic mass spectral analyses of the photoproducts of dTpdT and dTpdU

The photoproducts of the dinucleoside monophosphates dTpdT and dTpdU have been examined by thermospray high‐performance liquid chromatography/mass spectrometry in the positive and negative ion modes. The photo‐products included the cis‐syn and trans‐syn cyclobutane dimers, the 6–4 and Dewar 6–4 pyrimidine‐pyrimidinone photoadducts and the uracil photohydrates of dTpdU. Molecular ions and several fragment ions are observed in all cases. It is shown that the cyclobutane dimers, 6–4 photoadducts and Dewar 6–4 photoadducts can be easily distinguished from each other and from the parent dinucleoside monophosphates by fragmentation pattern differences. Using single‐ion monitoring these photoproducts could be detected at the low‐picomole level.