Determination of 16 phthalate esters in sesame oil by isotope dilution liquid chromatography with tandem mass spectrometry

Phthalate esters are easily released from packing materials into fat-rich food resulting in contamination of edible oil. This work focuses on the major aspects concerning the accurate and precise quantification of 16 phthalate esters in edible oil by isotope dilution liquid chromatography – tandem mass spectrometry, which will be helpful in the determination of the true quantity of phthalate esters from a metrological point of view. Oil samples were extracted using acetonitrile and n-hexane and then cleaned-up using a PSA SPE cartridge. Critical isomers were well separated on a ZORBAX SB-phenyl column under gradient elution followed by positive ESI-MS/MS mode. The approaches taken to optimize sample handling, the solvent, and the LC system helped to reduce blank interferences and thereby improved the LOD for DBP, DEHP, DEP and BBP by 50%. Quantification was based on the measurements of the mass ratios of the natural and corresponding isotopically labeled D4 internal standards in the sample by using a single-point calibration. The spiking recoveries of 16 analytes ranged from 88.6 to 105.6% with relative standard deviation values between 0.3 and 7.5%. The detection limits for 16 analytes were in the range of 0.21–28.2 ng g−1. The relative expanded uncertainties were from 4.2 to 15%. Together with the decrease of blank interference, superior selectivity for isomeric mixtures and use of isotopically labeled internal standards, the method was confirmed to be a reference method to provide an accurate basis to determine trace phthalate esters in edible oil.