RESUMO
Huolinguole lignite was sequentially extracted with carbon disulfide, ethyl acetate, methanol and acetone.All of the extracts were analyzed using a time-of-flight mass spectrometry (TOF-MS) equipped with an atmospheric pressure photoionization (APPI) ion source.Toluene or 1,4-difluorobenzene was chosen as dopant for APPI.The results indicated that both dopants could well ionize compounds which could not be ionized by APPI without dopant.Toluene induced higher ionization efficiency than 1,4-difluorobenzene.Some compounds in the extracts were identified as dimers, which might be formed via molecular association.Heteroatoms were identified in all of the associated molecules.Molecular weight distributions under three APPI ionization modes were similar.Compounds with molecular weight from 200 to 500 Da occupied 60% of all the products and around 10% of the products had molecular weight over 500 Da.