The supernatant was transferred into a glass tube and concentrated to near-dryness under a gentle nitrogen stream. Finally, 0.5 mL of methanol was added and vortex mixed for analysis by HPLC-MS/MS. The ethyl acetate extractable fraction, without the addition of glucuronidase, represented concentrations of “free” forms of parabens and p-HB. The “total” concentrations (free plus conjugated) were determined from an aliquot of urine by enzymatic deconjugation prior to extraction. Briefly, 300 μL of 1.0 M ammonium acetate, which contained 22 units of β- glucuronidase (prepared by spiking 50 μL ofβ-glucuronidase into 100 mL of 1.0 M ammonium acetate solution), and 5 ng of each of 13C6-MeP, 13C6−BuP, and 13C6-p-HB were added into 500 μL of urine. After incubation at 37 °C for 12 h, the digested samples were extracted by LLE, as described above.