We have developed a new high performance liquid chromatograph (HPLC) system with on-line sample pretreatment technique, which is used for on-line enrichment of polycyclic aromatic hydrocarbons (PAHs) in atmospheric particulates.Usually collected PAHs are extracted by acetonitrile, and then it is evaporated to adjust a concentration of target samples.However, this evaporation step is a time-consuming, and may have a possibility to loss target samples.The newly developed system allows us to inject a large amount of sample volume such as 1000 μL without any lose of recovery.