[Determination of furanoterpenoid toxins from sweet potato by thin-layer chromatography]

Sweet potato root tissue, when infected with different pathogens, invaded by insects, or irritated by certain chemicals, turns black-brown and produces and accumulates a large amount of furanoterpenoids such as ipomeamarone, ipomeamaronol, ipomeanine and 4-ipomeanol, which are toxic to animals. The furanoterpenoids from sweet potato root tissues infected with Ceratocystis fimbriata were extracted with ether. The extract solution was washed with 5% Na2CO3 and followed with distilled water and dried with dehydrated sodium sulfate (Na2SO4). The resulting ether extract was evaporated and the residue (crude sample) was dissolved in a small volume of chloroform. The determination of furanoterpenoid toxins was made on the plates at 20 degrees C and 30 degrees C respectively. The chloroform-soluble fraction was spotted on a silica gel G thin-layer plate and developed using different solvent systems, n-hexane and ethylacetate (4:1, V/V) , benzene and methanol (9:1, V/V) and petroleum ether and ethylacetate (2:1, V/V), until the solvent front migrated 10 cm from the starting spots. After development, Ehrlich's reagent was sprayed on the plate to detect the compounds. In the experiment, pure ipomeamarone and ipomeamaronol were used as standards. Thin-layer chromatograms on silica gel plates showed the furanoterpenoids were resolved effectively. The repeatability of Rf value was good. The resolution was the best in the solvent systems of benzene-methanol and petroleum ether-ethylacetate at 20 degrees C. After spraying Ehrlich's reagent, ipomeamarone (C) appeared as a light pink spot which soon changed to a dark gray, ipomeamaronol (A) as a purple red spot, compound B and D as a purple red and a gray spot respectively. Compound A, B, C and D had Rf values of 0.05, 0.14, 0.55 and 0.64 (n-hexane-ethylacetate), of 0.15, 0.29, 0.61 and 0.71 (petroleum ether-ethylacetate), of 0.40, 0.55, 0.71 and 0.79 (benzene-methanol), respectively. The separated spots were scanned by CS-930 TLC scanner at 527 nm and quantitative determination by external standard calibration. Ipomeamarone was detected by thin-layer chromatography and the limits of detection were 0.005 microg for pure and 0.02 microg for crude sample.