Fig. 3.

Characterization of a digital polymer coded with an invisible monomer ink. ESI-HRMS spectra obtained in the negative ion mode for polymer P10 before (a) and after (b) light exposure. Squares and circles indicate synthesis impurities. Open and full dark gray diamonds indicate photo-deprotection by-products. See Supplementary Fig. 6 for interpretation. c MS/MS sequencing of the irradiated polymer P10′. This spectrum was obtained by collision-induced dissociation of the [P10′-3H]³⁻ precursor ion. The inset schematizes the fragmentation pattern of a phosphate repeat unit. Dark gray stars indicate secondary fragments including deprotonated repeat units at m/z 153.0 and m/z 288.0