Pressure sensitive adhesives for the determination of dimethyl phthalate formic acid, diethyl phthalate formic acid, diisobutyl phthalate formic acid, dibutyl phthalate formic acid, butyl benzyl phthalate formic acid, di (2-ethylhexyl) phthalate formic acid, di-n-octyl phthalate formic acid, diisonononyl phthalate formic acid and diisodecyl phthalate formic acid by liquid chromatograph mass spectrometry. Pressure sensitive adhesive is suitable for the determination of these 9 kinds of o-formic acid esters. The sample was sonically dissolved with ethyl acetate, methanol precipitated polymer and Supernatant solution were filtrated, and then determined and confirmed by liquid chromatograph - Mass Spectrometer, and quantified by external standard method. Reagents and materials include methanol, ethyl acetate, acetonitrile, dimethyl phthalate formic acid, diethyl phthalate formic acid, etc.