Liquid-liquid extraction combined with online cleanup for the simultaneous determination of PAHs by GC-MS/MS and their hydroxylated metabolites by LC-MS/MS in human fingernails

Abstract

A method was developed for the simultaneous determination of polycyclic aromatic hydrocarbons (PAHs) and their hydroxylated metabolites (OH-PAHs) in human fingernails using liquid-liquid extraction and online purification. After surface decontamination by rinsing with acetone, the fingernails were digested with sodium hydroxide and subjected to liquid-liquid extraction with a mixture of n-hexane and methyl tertbutyl ether. The organic extract was then fractionated using a silica-based solid-phase extraction (SPE) cartridge to obtain a PAH fraction eluted with n-hexane/dichloromethane (v/v, 95:5) and an OH-PAH fraction eluted with dichloromethane/ethyl acetate (v/v, 50:50). The PAH fraction was directly injected into an online gel permeation chromatography-gas chromatography-triple quadrupole tandem mass spectrometry (GPC-GC-MS/MS) system, enabling rapid determination of 16 PAHs. A parallel online SPE liquid chromatography tandem mass spectrometry (LC-MS/MS) method was used to determine 12 OH-PAHs. Validation experiments showed that the recovery of PAH and OH-PAH were within range of 67.4%-105.1% (RSD ≤ 10.1%) and 72.8%-102.3% (RSD ≤ 10.9%), respectively, with limits of quantitation (LOQ) of 0.06-0.8 ng/g and 0.15-3.1 ng/g, respectively. Forty-two human fingernail samples from residents of Southern China were analyzed to establish background PAH and OH-PAH levels in this region. Several PAHs and OH-PAHs were detected, at concentrations of 97.5 to 3,687 ng/g for PAHs and 24.2 to 767 ng/g for OH-PAHs. The dominant homologues were two- and three-ring PAH isomers, notably naphthalene (Nap), fluorene (Flu), and phenanthrene (Phe), as well as the corresponding hydroxylated metabolites 2-OH-Nap, OH-Flu, and OH-Phe. Smoking, consuming barbecued food, and age had no significant effects on PAH exposure, but a larger sample would be required to confirm this finding. The online purification strategy presented here expedites cleanup and purification during analysis of human fingernails and should facilitate non-invasive biomonitoring of PAHs in humans, particularly when analyzing large numbers of samples.

Keywords: Fingernail; OH-PAHs; Online gel permeation chromatography; Online solid phase extraction; PAHs.