This work describes a new analytical method useful for monitoring the human exposure to the endocrine-disrupting plasticizer triphenyl phosphate (TPP) via nail polish use. The method allows trace determination of this parent compound and its main metabolite, namely diphenyl phosphate (DPP), in urine samples of nail polish users. The method is based on a novel microextraction technique termed stir bar sorptive-dispersive microextraction (SBSDME) using a magnetic composite made of CoFe2O4 magnetic nanoparticles embedded into a mixed-mode weak anion exchange polymer (Strata™-X-AW), followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The main parameters involved in the extraction procedure were evaluated and optimized. Under the optimized conditions, the method was successfully validated showing good linearity (at least up to 100 ng mL-1) and enrichment factors (17 and 30), limits of detection and quantification in the low ng L-1 range (1.9-17.1 ng L-1 and 6.3-57.1 ng L-1, respectively) and good intra- and inter-day precision (RSD < 8%). Excellent recoveries (81-112 %) were achieved by using matrix-matched calibration for quantification. Finally, the method was applied to the determination of both the parent compound and the metabolite in human urine samples from volunteers who applied themselves a nail polish containing TPP. Detectable amounts of the parent compound were found just in the first urination, whereas quantifiable amounts of DPP were found in the low ng mL-1 range even 24 h after application of the nail polish, thus suggesting a rapid biotransformation and a low excretion, and showing DPP as excellent biomarker of human exposure to TPP. This work expands the analytical potential of the novel SBSDME, and the proposed methodology contributes to the study of the absorption/excretion levels of endocrine disruptors present in cosmetic products.