Abstract: Three red pigments r1, r2 and r3 were extracted and separated from Potamogeton crispus L, the UV-Vis spectra, FT-IR spectra, test by chemical reaction and Mass spectra were studied. The visible spectra of r1, r2 and r3 in acetone, methanol, ethanol, chloroform and carbon disulphide had only a single, rounded, almost symmetrical absorption peak, the shape of visible spectra was similar to that of canthaxanthin and astaxanthin. but the visible spectra of them in hexane had a asymmetrical absorption peak that were approximate to the "three-peaked spectra"; but the visible spectra of β-carotene(non-oxocarotenoids) was typical "three-peak spectra". As compared with the spectra in hexane, the λmax of r1, r2 and r3 increased along with the strengthening in solvents polarity, and the shape, fine structure and λmax of their spectra were greatly affected by the solvents. The average λmax of r1, r2 and r3 in the six solvents were larger than that of astaxanthin, canthaxanthin and β-carotene, respectively. The FT-IR spectra of r1, r2 and r3 showed the characteristic frequencies of polyene chain compounds containing carbonyl groups (there were differences in 1 660-1 750 cm-1 ). The test by chemical reaction showed that r1, r2 and r3 were carotenoids containing carbonyl groups ( not 5, 6 or 5, 8-Epoxides). It is an important evidence to prove that r1, r2 and r3 are carotenoids containing carbonyl groups and having molecular formula C40H50O2 , molecular weight 562 determined by low and high resolution EI-MS. They have no identical structure with canthaxanthin, astaxanthin and β-carotene. The results show that r1, r2 and r3 are the isomers of rhodoxanthin.

Key words: Potamogeton crispus L., Red carotenoids, Rhodoxanthin, UV-Vis spectra, FT-IR spectra, Mass spectra