Optimized extraction method for LC–MS determination of bisphenol A, melamine and di(2-ethylhexyl) phthalate in selected soft drinks, syringes, and milk powder

Described below is an optimized solid-phase extraction method (SPE) for the simultaneous determination of three hazardous plastic additives. Two high-performance liquid chromatographic–electrospray ionization-mass spectrometric (HPLC–ESI-MS) methods were developed and validated to estimate the melamine (MEL), bis(2-ethylhexyl) phthalate (DEHP), and bisphenol A (BPA) contents in drinking water, syringes, soft drinks, and dry milk powder. One extraction procedure optimally recovered all three substances from the different matrices. Two extraction columns were combined and included a silica gel LiChroprep RP-2 column (20:1, g/g, top column) and a Sep-Pak with a C18 column (500 mg, bottom column). The analytical column was an Agilent Eclipse XDB-C8 column, 4.6 mm × 150 mm, 5 μm, maintained at 50 ± 2 °C. MEL and DEHP were monitored by positive triple quad mass spectrometry (TQ-MS) using an acidic mobile phase, while BPA was monitored by negative TQ-MS using a mobile phase containing a 0.05% ammonia solution. The general linear range of the three compounds ranged from 12 to 1000 pg/μL in the injected solution (25 μL). The average extraction recoveries were within the range of 83.0–102.5%. Relatively high concentrations of BPA and DEHP were found in the milk powder and sterile syringes.