environmental water by liquid chromatography-mass spectrometry（LC-MS） coupled with ultrasonic assisted extraction with ionic liquid.An ionic liquid,1-butyl-3-methylimidazolium hexafluorophosphate（［C4mim］［PF6］）,was used as extraction solvent to extract PCP in water samples.The extraction parameters,such as sample volume,temperature,ultrasonic extraction time,inorganic salt concentration and solution pH value were investigated.The chromatographic separation was performed on a XDB C18（150 mm×2.1 mm,5 μm） column with a mobile phase of methanol-2 mmol/L ammonium acetate solution（70∶30）.Detection was carried out by LC-MS using a negative electrospray ionization interface under the selected ion monitoring（SIM） mode.The calibration curve was linear within the range of 0.005-1.0 μg?L-1 with a correlation coefficient of 0.999 2.The limit of quantitation（LOQ） was 0.005 μg?L-1.The extraction recoveries were between 91.0% and 97.0%,and the intra-day RSDs were between 1.1% and 5.4%,and the inter-day RSDs were between 3.8% and 8.3%.The developed method was simple,accurate and specific,and could be used for the determination of trace PCP in environmental water.