Evaluation of a method for phthalate extraction from milk related to the milk dilution ratio

Liquid–liquid extraction techniques coupled with gas chromato­graphy–mass spectrometry (GC–MS) were compared for the extraction and the determination of four phthalates: dimethyl phthalate (DMP), di- n -butyl phthal­ate (DBP), benzyl butyl phthalate (BBP) and di-(2-ethylhexyl) phthalate (DEHP) in six different kinds of milk-based samples. Extraction factors: sample preparation, organic solvent type and volume, salt effect, agitation and the extraction time were optimized. The ions of the base peak ( m / z  149 for DBP, BBP and DEHP and  m / z  163 for DMP) for the investigated phthalates were selected for the screening studies. The acquisition was performed in the selected ion-monitoring mode.  The response of the mass selective detector (MSD) for GC–MS phthalate calibration standards was linear between 0.25 and 2.50 µg mL -1  with calculated limit of detection ( LOD ) values between 0.01 to 0.04 µg mL -1  and limit of quantitation ( LOQ ) values of 0.05 to 0.12 µg mL -1 , while repeatability was between 1.7 to 4.9 % relative standard deviation ( RSD ). The study demonstrated an increase in the recovery of less polar phthalates in matrix milk standards on matrix dilution. Recovery for hydrophilic phthalates, such as DMP, was not changed by matrix dilution and it was continuously low for the investigated method. Two spiking levels, tested for the influence of matrix dilution on phthalate recovery, showed the same trend.