“…A number of reviews on PC of heterocyclic nitrogen compounds have appeared in "Paper Chromatography" (721, 1219, 1220, 1221, 1619). Reports have appeared on TLC of various aromatic (1502) and heterocyclic (1540,1851) nitrogen compounds, on the chromatography of various pyridines (302, 672, 1521a, 1542, 2165), pyrazoles (678, 2O4O), imidazoles (686,1042), porphines (86), cinnolines (669), carbazoles (128, 574, 578), indoles (88,359,881,449,1064,1599,1921), and polynuclear aza-heterocyclic compounds (1203,1765,1770).…”