Atmospheric pressure photoionization mass spectrometry of oligodeoxyribonucleotides

Is methanol a dopant under atmospheric pressure photoionization conditions?

Using a modified atmospheric pressure photoionization (APPI) source coupled to a tunable vacuum ultraviolet source at the SOLEIL synchrotron radiation facility, we determined the appearance energy of protonated methanol monomer and dimers at different source temperatures. The experimental data indicated that protonated monomers can be formed through the direct photoionization of neutral methanol by the second emission band of a krypton discharge UV lamp at 116.49 nm (10.64 eV) explaining why methanol can be considered as a weak dopant under APPI conditions. This point is in contradiction with the previously proposed mechanism where photoionization of methanol dimer was followed by the dissociation of the protonated methanol dimer into protonated methanol monomer.

Radiation-induced formation of 2',3'-dideoxyribonucleosides in DNA: a potential signature of low-energy electrons

We have identified a series of modifications of the 2'-deoxyribose moiety of DNA arising from the exposure of isolated and cellular DNA to ionizing radiation. The modifications consist of 2',3'-dideoxyribonucleoside derivatives of T, C, A, and G, as identified by enzymatic digestion and LC-MS/MS. Under dry conditions, the yield of these products was 6- to 44-fold lower than the yield of 8-oxo-7,8-dihydroguanine. We propose that 2',3'-dideoxyribonucleosides are generated from the reaction of low-energy electrons with DNA, leading to cleavage of the C3'-O bond and formation of the corresponding C3'-deoxyribose radical.

Atmospheric pressure photoionization as a powerful tool for large-scale lipidomic studies

Lipidomic studies often use liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) for separation, identification, and quantification. However, due to the wide structural diversity of lipids, the most apolar part of the lipidome is often detected with low sensitivity in ESI. Atmospheric pressure (APPI) can be an alternative ionization source since normal-phase solvents are known to enhance photoionization of these classes. In this paper, we intend to show the efficiency of APPI to identify different lipid classes, with a special interest on sphingolipids. In-source APPI fragmentation appears to be an added value for the structural analysis of lipids. It provides a detailed characterization of both the polar head and the non polar moiety of most lipid classes, and it makes possible the detection of all lipids in both polarities, which is not always possible with ESI.