“…In general, analytical approaches include an extraction stage using low polarity solvents, such as chlorobenzene, methanol, dimethylsulfooxide, acetonitrile and dimethylformamide [15,16]. HPLC has been widely deployed for molecular separation, particularly with UV-Vis or fluorescence detection systems [4,17], due to the abundant chromophores usually present in the azo pigments, although hyphenated mass spectrometry detectors have also been used [15,[18][19][20]. Minimally invasive analyses with vibrational spectroscopy techniques such as Raman scattering have been reported [21][22][23][24][25], including applications in the field of modern art [21,25,26].…”