Magnetic solid-phase extraction based on magnetic multi-walled carbon nanotubes for the determination of phthalate monoesters in urine samples

Abstract

In this study, magnetic carbon nanotubes (MCNTs) were prepared by assembling magnetic nanoparticles onto the acid-treated multiwall carbon nanotubes (MWCNTs). Due to their excellent adsorption capability, the MCNTs were used as adsorbent of magnetic solid-phase extraction (MSPE) to extract phthalate monoesters (PMEs), the main biomarkers of phthalate exposure, from human urine. By coupling MSPE with gas chromatography–mass spectrometry (GC–MS), a reliable, sensitive and cost-effective method for the simultaneous determination of five main PMEs including monomethyl phthalate (MMP), monoethyl phthalate (MEP), mono n-butyl phthalate (MBP), mono-(2-ethylhexyl) phthalate (MEHP) and monobenzyl phthalate (MBzP) was developed. The factors that could influence the extraction, including the amount of magnetic nanoparticles, pH of sample solution, extraction and desorption time, the amount of salt addition, the type and volume of desorption solvent were investigated in detail. Under optimized conditions, the LODs and LOQs achieved were in the range of 0.025–0.050 and 0.125–0.250ngmL−1 respectively. And calibration curves were linear (r2≥0.992) over the concentration ranges from 0.250 to 250ngmL−1. In addition, a satisfying reproducibility was achieved by evaluating the intra- and inter-day precisions with relative standard deviations (RSDs) less than 11.2% and 11.4%, respectively. The recoveries of the five PMEs ranged from 92.6% to 98.8% with the RSDs less than 10.7%. Finally, the established MSPE-GC–MS method was successfully applied to determine PMEs in human urine samples. MMP, MEP, MBP and MEHP were detected in most of the samples with the median concentration of 8.46, 9.26, 13.60, and 5.95ngmL−1 respectively. MBzP was detected in 58.3% of the samples with the median concentration of 3.05ngmL−1. Taken together, the MSPE-GC–MS method developed in current study provides a new option for the determination of PMEs in human urine.