[Determination of 16 organophosphate esters in human blood by high performance liquid chromatography-tandem mass spectrometry combined with liquid-liquid extraction and solid phase extraction]

Abstract

Measurement of organophosphate esters (OPEs) in human body fluids is important for understanding human internal exposure to OPEs and for assessing related health risks. Most of the current studies have focused on the determination of OPE metabolites in human urine, as OPEs are readily metabolized into their diester or hydroxylated forms in the human body. However, given the existence of one metabolite across multiple OPEs or multiple metabolites of one OPE, as well as the low metabolic rates of several OPEs in in vitro studies, the reliability of urinary OPE metabolites as biomarkers for specific OPEs is needs to be treated with caution.Human blood is a matrix that is in contact with all body organs and tissues, and the blood levels of compounds may better represent the doses that reach target tissues. Currently, only a few studies have investigated the occurrence of OPEs in human blood by different analytical methods, and the variety of OPEs considered is limited. In this study, a method based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed for the simultaneous determination of 16 OPEs in human blood, and the extraction efficiency of the solid phase extraction (SPE) column for OPEs was verified. To human blood samples, 10 ng of an internal standard was added, followed by mixing and aging for 30 min. The samples were extracted three times with acetonitrile using a shaker, and then purified on ENVI-18 cartridges with acetonitrile containing 25% dichloromethane as the eluent. Finally, the OPEs were analyzed by high performance liquid chromatography-tandem mass spectrometry. After optimization of the analytical column and mobile phases, the analytes were separated on a BEH C18 column (100 mm×2.1 mm, 1.7 μm) by gradient elution using methanol and 5 mmol/L ammonium acetate in water as the mobile phase. Then, the analytes were ionized in electrospray ionization positive (ESI⁺) mode and detected in the multiple reaction monitoring (MRM) mode. The mass spectral parameters, including the precursor ion, product ion, declustering potential, entrance potential, and collision cell exit potential, were optimized. The results were quantified by the internal standard method. The limits of detection (LOD, S/N=3) of the OPEs were in the range of 0.0038-0.882 ng/mL. The calibration curves for the 16 OPEs showed good linear relationships in the range of 0.1-50 ng/mL, and the correlation coefficients were >0.995. The extraction efficiency of the ENVI-18 column for the 16 OPEs was validated, and the average recoveries of the target compounds were 54.6%-104%. The average recoveries (n=3) of 15 OPEs, except trimethyl phosphate (TMP), in whole blood at three spiked levels were in the range of 53.1%-126%, and the relative standard deviations (RSDs) were in the range of 0.15%-12.6%. The average recoveries of six internal standards were in the range of 66.8%-91.6% except for TMP-d9 (39.1%), with RSDs of 3.52%-6.85%. The average matrix effects of the OPEs in whole blood were 56.4%-103.0%. Significant matrix effects were found for resorcinol bis(diphenyl phosphate) (RDP) (75.8%±1.4%), trimethylphenyl phosphate (TMPP) (68.4%±1.0%), 2-ethylhexyl di-phenyl phosphate (EHDPP) (56.4%±12.4%), and bisphenol-A bis(diphenyl phosphate) (BABP) (58.5%±0.4%). However, these effects could be corrected by similar signal suppressions of the corresponding internal standard (TPHP-d15, 77.4%±7.5%). This method is simple, highly sensitive, and suitable for the determination of OPEs in human blood. Fifteen human whole blood samples were collected to quantify the 16 OPEs using the developed method. The total concentrations of the OPEs ranged from 1.50 to 7.99 ng/mL. The detection frequencies of eight OPEs were higher than 50%. Tri-iso-butyl phosphate (TiBP), tri(2-chloroethyl) phosphate (TCEP), and tri(1-chloro-2-propyl) phosphate (TCIPP) were the dominant OPEs, with median concentrations of 0.813, 0.764, and 0.690 ng/mL, respectively. These results indicated widespread human exposure to OPEs, which should be of concern.

Keywords: high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS); human blood; liquid-liquid extraction (LLE); organophosphate ester; solid phase extraction (SPE).

图 1. 16种OPEs标准品的总离子流色谱图