Determination of organophosphate esters and their metabolites in hair by high performance liquid chromatography-tandem mass spectrometry

Organophosphate esters (OPEs) are widely used in daily life and can be rapidly metabolized into diester metabolites (di-OPEs) upon entering the human body. An effective method was developed for the analysis of 10 OPEs and 8 di-OPEs in hair using high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). After pulverization, 0.1 g of hair powder was sonicated with 4 mL of a n-hexane/ethyl acetate/methanol mixture (1:1:1, V/V/V) for three times. The organic phase was then purified using 100 mg of C18 (octadecyl bonded silica) and 20 mg of anhydrous sodium sulfate. The supernatant was concentrated by nitrogen flow and subsequently analyzed by HPLC-MS/MS. The chromatographic mobile phase consisted of methanol and 0.01 mol·L−1 ammonium acetate aqueous solution. Ion scanning was performed in both positive and negative ion modes. Under the optimized conditions, both OPEs and di-OPEs showed good linearities in the 0.2—500 ng·mL−1 concentration range (R2 > 0.995). The average recoveries of OPEs in hair ranged from 60.3% to 128%, with RSD values ranging from 0.6%—19.8%, while those of di-OPEs ranged from 60.7% to 125%, with RSD values ranging from 1.43%—17.5%. The detection limits of OPEs and di-OPEs were 0.08—6.59 ng·g−1 and 0.23—5.42 ng·g−1, respectively. This method was used to determine OPEs and di-OPEs in 18 hair samples. Results showed that the median concentrations of 10 OPEs ranged from nd to 27.3 ng·g−1, and triphenyl phosphate (TPHP), tris(2- chloropropyl) phosphate (TCPP), and tris(2-butoxyethyl) phosphate (TBOEP) were detected in all samples. The median concentrations of 8 di-OPEs ranged from nd to 38.4 ng·g−1, and the detection frequencies of diphenyl phosphate (DPHP), bis(1,3-dichloro-2-propyl) phosphate (BDCPP), and dibutyl phosphate (DBP) were 100%. Our method provides reliable technical support for the comprehensive assessment of OPEs and di-OPEs exposure levels in humans.