The present invention discloses a method for derivatizing carcinogenic 3- monochloropropanediol, 3-MCPD and 1,3-dichloropropane, 1,3-DCP simultaneously in food sample using hexamethyldisilazane, HMDS derivatizing agent combined with trimethylsilyl trifluoromethanesulfonate TMSOTf catalyst at room temperature. The method disclosed accroding to the present invention only requires a short period of time, cost effective, sensitive with high accuracy of the analytical method is demonstrated with real food samples.