Development of a headspace solid-phase microextraction method combined with gas chromatography mass spectrometry for the determination of phthalate esters in cow milk

Phthalate esters released from plasticized polyvinyl chloride (PVC) tubing into raw cow milk during milking at dairy farms could be a potential source of contamination by phthalate esters in dairy products. A method was developed for the determination of these phthalate esters in raw cow milk samples using a headspace solid-phase microextraction (HS-SPME) technique. The milk samples were mixed with sodium chloride and extracted for 60 min at 90 °C. The phthalates collected on the SPME fibre were then desorbed in the GC injection port followed by GC-MS analysis in single ion monitoring (SIM) mode. The extraction efficiency of the SPME fibre was dependent on the fat content in the milk sample. Since the fat content in each cow milk sample was different, a combined standard addition and internal standard method was used for the quantification of the phthalate esters in milk samples. The recoveries at two spiking levels were over 90% except for dimethyl phthalate. The method detection limit for di-(2-ethylhexyl) phthalate (DEHP) was from 0.31 to 3.3 ng g−1 for samples containing up to 10.8% fat. This method was sufficiently sensitive to detect di-(2-ethylhexyl) phthalate, dibutyl phthalate (DBP) and diethyl phthalate (DEP) in two groups of raw cow milk samples (cow milk samples collected using and without using PVC tubing). While similar levels were found in both types of samples for DBP and DEP, the level of DEHP was much higher in samples collected using PVC tubing (215.36 ng g−1) than once without (16.04 ng g−1), indicating potential leaching of DEHP from PVC tubing into raw cow milk.