Fig. 2. Liquid chromatography–mass spectrometry (LC-MS) chromatogram of a mixture of 2.0 mg/L 1,5-naphthalendisulfonic acid disodium salt (NDS) standard solution and 2.0 mg/L persulfate standard solution. Cromatographic conditions: see method I in LC-MS analysis (experimental session). MS detection. Peak identification: 6.11 min NDS.