Abstract:Liquid chromatography -mass spectrometry （LC -MS/MS）was established to determine the composition and content of coumarins in 6 different varieties of grapefruit skin of Citrus maxima，by ultrasonic extraction with methanol，and Oasis HLB solid phase extraction column purification with Waters XBrigde C18 column separation，and gradient with acetonitrile and 0.05 mol/L ammonium acetate solution（containing 0.1%formic acid）as mobile phase elution，and detected by multiple reaction monitoring（MRM）.The results showed that 8 coumarins and their derivatives had a good linear relationship（R2≥0.999 5）in the range of 0.010 μg/mL to 1.0 μg/mL.The detection limit of the method was from 3.0 μg/kg to 4.5 μg/kg，and the limit of quantification was from 10.0 μg/kg to 15.0 μg/kg；the recoveries were from 90.4 % to 98.5 %，and the relative standard deviations were from 0.9%to 4.1%.7-methylcoumarin，7-methoxycoumarin，7-ethoxy-4-methylcoumarin，acenocoumarol were detected in grapefruit skin of Citrus maxima.Among them，the content of 7-methoxycoumarin was relatively high，and the content was 11.4 μg/kg-123.7 μg/kg.This ingredient may be related to the therapeutic effect of grapefruit with warm stomach，phlegm and moisturizing throat，which provides comprehensive development and utilization of grapefruit skin of Citrus maxima.