Identification of isomers and subsidiary colors in commercial Fast Green FCF (FD&C Green No. 3, Food Green No. 3) by liquid chromatography-mass spectrometry and comparison between amounts of the subsidiary colors by high-performance liquid chromatography and thin-layer chromatography-spectrophotometry.

The existence of five of the six expected isomers in commercial Fast Green FCF (G3: Food Green No. 3, FD&C Green No. 3, CAS No. 2353-45-9, C.I. No. 42053), the main product of which is m,m-G3 and the sub-products of which are presumed to be m,p-G3, o,m-G3, p,p-G3, o,p-G3 and o,o-G3, was confirmed using LC/MS, and the levels of the isomers, m,m-G3, m,p-G3, p,p-G3, o,m-G3 and o,p-G3, were determined by analytical HPLC. The existence of seven subsidiary colors that were decomposed from G3 was also confirmed using LC/MS. The levels of the subsidiary colors in ethanol extracts from TLC were determined by HPLC and spectrophotometry, and these results were compared. It was clear that the values determined by TLC-spectrophotometry were higher than those by HPLC. It was recommended that the levels of subsidiary colors in G3 should be determined by HPLC.