MS/MS spectra of PSss12 by (a) EPD of 4-• (one UV pulse, 5 mJ; then 8% normalized collision energy, 30 ms), and (b) CID 4- (8% normalized collision energy, 30 ms). Precursor ions are noted with a star. Bolded and italicized product ions retain the modification. Not all of the EPD product ions are labeled due to the complexity of the spectrum. A summary of the product ions formed from EPD and CID for the phosphorothioate single strand 12-mer (c), in which the slash marks represent cleavages at that location. A star above the slash mark represents a product containing the phosphorothioate modification. The phosphorothoate modification is shown as an s in the sequence.