Determination of phthalate esters in cow milk samples using dispersive liquid-liquid microextraction coupled with gas chromatography followed by flame ionization and mass spectrometric detection

A simple and economic method for the analysis of phthalate esters, dimethyl phthalate, diethyl phthalate, di‐iso‐butyl phthalate, di‐n‐butyl phthalate, and di‐2‐ethylhexyl phthalate in cow milk samples by means of gas chromatography–flame ionization detection and gas chromatography–mass spectrometry has been developed. In this work, NaCl and ACN were added to 5 mL of the milk sample as the salting out agent and extraction solvent, respectively. After manual shaking, the mixture was centrifuged. In the presence of NaCl, a two‐phase system was formed: upper phase ‐ acetonitrile containing phthalate esters –and lower phase – aqueous phase containing soluble compounds and the precipitated proteins. After the extraction of phthalate esters from milk, a portion of supernatant phase (acetonitrile) was removed, mixed with 1,2‐dibromoethane at microliter level and injected by syringe into NaCl solution. After the extraction of the selected phthalate esters into 1,2‐dibromoethane, phase separation was performed by centrifugation and the enriched analytes in the sedimented phase were determined by gas chromatography‐flame ionization detection and gas chromatography–mass spectrometry. Under the optimum extraction conditions, low limits of detection and quantification between 1.5–3 and 2.5–11 ng/mL, respectively was observed. Enrichment factors were in the range of 397–499. The relative standard deviations for the extraction of 100 ng/mL of each phthalate ester were in the range of 3‐4% (n = 6). Finally, some milk samples were successfully analyzed using the proposed method and two analytes, di‐n‐butyl phthalate and di‐2‐ethylhyxel phthalate, were determined in them in nanogram per milliliter level.