MS and in-trap collision induced dissociation multi-stage spectra(CID-MSn) under the positive scanning mode were studied for 1-phenyl-3-methyl-pyrazolone-5 by using electrospray ionization-mass spectrometry(ESI-MS),the fragmentation law of fragmental ions derived from the keto and enol isomers of this compound were discussed about and the corresponding fragmentation pathway was given.
