Fig. 3. Liquid chromatography–mass spectrometry (LC-MS) chromatogram of a solution containing 1,5-naphthalendisulfonic acid disodium salt (NDS) and persulfate (each 0.13 mM) after 20.0 min of the degradation process. Cromatographic conditions: see method II in LC-MS analysis (experimental session). Detector MS. Peak identification: 7.31 min NDS (Fig. 3a), 6.66 min intermediate I (Fig. 3b). Mass spectra of NDS [M – 2Na⁺H]^– at 287 m/z (Fig. 3c) and of intermediate I at 303 m/z (Fig. 3d).