Ultra-High-Performance Liquid Chromatography-Isotope Dilution Tandem Mass Spectrometry for the Determination of Phthalate Secondary Metabolites in Human Serum Based on Solid-Phase Extraction

Background: A multitude of biomonitoring analytical methods are applied in urinary detection, but few are applicable to phthalate metabolites in human serum, and those that are invariably involve complex operation. Objective: To develop a novel method for the determination of phthalate monoesters in human serum using solid-phase extraction (SPE) and ultra-HPLC (UHPLC)-tandem mass spectrometry for multiple human serum sample determination. Method: Analytes in serum samples were extracted and purified with a novel SPE cartridge named Prime HLB and then directly injected and analyzed without eluent redissolution. After sample extraction and cleanup, 11 phthalate monoesters were separated on a C18 chromatographic column in UHPLC. Among them, mono-isobutyl phthalate and mono-n-butyl phthalate, a pair of isomers, were successfully separated. Results: Lower LODs of the 11 monoesters in 0.5 mL human serum were in the range of 0.03–3 ng/mL, and lower LOQs accordingly ranged from 0.1 to 10.0 ng/mL. Recoveries from spiked bovine serum samples were in the range of 95.3–109.9%, and RSDs were 8.0–12.0%. Intra- and inter-day recoveries were in the range of 94.1–115.7%, with RSDs <13.7%. Conclusions: The proposed method has been proved to be rapid, simple, accurate, and sensitive, so that it may potentially be used for high-throughput biological monitoring with high efficiency and precision. Highlights: Sample pretreatment does not require eluent drying and redissolution. Mass losses of analytes are avoided. Operational procedures are easy and rapid. The method has proved applicable for 11 phthalate metabolites in multiple human serum sample determinations.