Determination of free and total phthalates in commercial whole milk products in different packaging materials by gas chromatography-mass spectrometry

We developed a method for extraction and determination of free and total phthalate esters in commercial whole milk products. The free phthalates in milk samples were extracted with ethyl acetate after general pretreatment procedures including protein precipitation, centrifugation, and filtration. The bound phthalates in samples were first desorbed with the aid of ultrasound irradiation before extraction of total phthalates. The separation and determination of phthalates in extracts was performed by gas chromatography coupled with mass spectrometric detection. The detection limits were in the range of 0.09 to 0.36 ng/g and the average recovery between 79.1 and 110.3%. The developed methods were applied to extract and determine phthalates in commercial whole milk products with different packaging materials, including plastic, glass, and metal. All samples contained several phthalates, including diethyl, diisobutyl, and bis(2-ethylhexyl) phthalates at concentrations between 2.60 and 156.4 ng/g. The identified phthalates occurred in both free and bound forms. The amounts of phthalates in milk samples packaged in glass and metal containers were much lower than those in plastic containers. Plastic packaging materials are a possible source of phthalate contamination in commercial whole milk products, and a considerable portion of bleached phthalates from packaging can be adsorbed on proteins and other solid components of milk.