Abstract: Objective To establish a rapid detection method for 16 phthalate esters（PAEs） in ambient air fine particulate matter（PM_2.5） by ultrasonic extraction ultra high performance liquid chromatography-tandem mass spectrometry. Methods The samples were collected onto a quartz filter membrane by a sampler equipped with the PM_2.5 cutting head. By comparing the extraction efficiency of different extraction solutions,selecting the appropriate extraction solution for ultrasonic extraction of the sample,comparing the separation effect and retention time of three chromatographic columns,16 types of PAEs were detected using ultra high performance liquid chromatography tandem mass spectrometry,and quantified using internal standard method to obtain indicators such as linearity and detection limit. An appropriate amount of standard was added to the quartz filter membrane to evaluate the recovery rate and precision of the method. Results The linear range of 16 PAEs compounds was within the range of 0.5 to 200 ng/mL,and all had good linear relationships,with R>0.995 0. Comparing the extraction effects of 50% methanol aqueous solution,50% acetonitrile aqueous solution,methanol and acetonitrile on the samples with the concentration of 10,50,100 μg/L after spiked,the average recovery of standard addition（n=3） was 71.45%-126.8%,51.71%-124.40%,68.62%-210.3% and 84.08%-110.28%. When using acetonitrile solvent for extraction,the recovery rates of three parallel samples were the most stable,and the recovery rates of 16 PAEs were all between 80% and 120%.When using T3 chromatographic column,all 16 PAEs were separated within 15 minutes,and the separation effect was better. The method precision was ≤7.95%,the detection limit was between 0.001 and 0.077 ng/m³,and the recovery rate was 83.8%-117.6%. Using this method,PM_2.5 samples（n=9） collected from the same outdoor sampling point in Shanghai from November to December 2021 at different periods were detected. A total of 7 phthalate ester compounds were detected,of which 5 had a detection rate of 100%,namely dimethyl phthalate（DMP）（0.26-6.39 ng/m³）,diethyl phthalate（DEP）（0.96-2.04 ng/m³）,and diisobutyl phthalate（DiBP）（9.46-63.40 ng/m³）,dibutyl phthalate（DBP）（2.52-44.60 ng/m³） and di-2-ethylhexyl phthalate（DEHP）（6.29-59.40 ng/m³）. Conclusion The spiked recovery rate of this method is stable,the detection limit is low,and the accuracy and sensitivity are high. The pre experimental processing steps are simple and the analysis time is short,which can be used for the detection of phthalate esters in PM_2.5.

Key words: Phthalate esters, Atmospheric fine particulate matter, Ultra high performance liquid chromatography-tandem mass spectrometry, Ultrasound extraction