HPLC Determination of 6 Phthalates in Soil and Evaluation of Its Biological Availability

Two portions (10.000 g. each) of the soil sample were taken, and one portion (10 mL) of methanol were added to extract the 6 phthalatesi.e., dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl benzyl phthalate (BBP), dibutyl phthalate (DBP), di-(2-ethyl)hexylphthalate (DEHP) and dioctylphthalate (DNOP), into the methanol phase with the aid of ultrasonotor for 30 min. Appropriate amounts of MgSO₄ and NaCl were added to the extract, and the mixture was centrifuged for 3 min. The supernatant was diluted to 10.0 mL and filtered through 0.45 μm filtering membrane. The filtrate was analyzed by HPLC. Zorbax Eclipse C₁₈ chromatographic column was used as stationary phase. Mixtures of acetonitrile (A) and water (B) with various ratios were used as mobile phase in the programmed gradient elution. And the 6 phthalates were determined by UV-detector at 245 nm. Linear relationships between values of chromatographic peak areas and corresponding mass concentrations of the 6 phthalates were found in the same range of 0.10-10.0 mg·L^-1. Detection limits found were in the range of 0.01-0.04 mg·L^-1. Another portion of the sample was treated by invitro gastrointestinal simulation with successive extractions in the following way:The sample was first extracted with 10 mL of the simulated gastric juice for 1 h at 37℃, to obtain the digestive juice, which, after adjusting its pH to 7.0 with NaHCO₃, and addition of 55.0 mg of bile salt and 15 mg of pancreatic secretin (acting as simulated intestinal juice) was extracted by vibration for 2 h at 37℃. After centrifuging for 3 min, the supernatant was taken and treated by the procedure given above beginning from extraction with methanol. It was found that the biological availability of the PAEs tended to giver lower rates as their fat-solubility are higher. In addition, the biological availability of the PAEs was also effected by physical and chemical properties of the soil.