title: Determination of total thyroxine in human serum by hollow fiber liquid-phase microextraction and liquid chromatography-tandem mass spectrometry.
abstract: Determination of total thyroxine in human serum using hollow fiber liquid-phase microextraction (HF-LPME) has been accomplished for the first time. HF-LPME serves as an inexpensive sample pretreatment and the cleanup method that is nearly solvent-free. Thyroxine was extracted through a water immiscible organic solvent immobilized in the wall pores of a polypropylene hollow fiber into 20μl of an aqueous acceptor phase inside the lumen of the hollow fiber. This technique produced extracts that had comparable cleanness with those obtained using solid-phase extraction (SPE). Serum samples with endogenous thyroxine were spiked with isotopically-labeled thyroxine and analyzed by liquid chromatography-tandem mass spectrometry after HF-LPME extraction. Extraction parameters including the organic phase, acid/base concentration of acceptor phase, stirring speed and extraction time were optimized. The calibration range was found to be linear over 1-1000ng/g with the limit of detection (LOD) of 0.3 ng/g. For quantification of total thyroxine in human serum, 6 subsamples were prepared and the results indicated very good precision with a relative standard deviation of <1.3%. The difference from the SPE method was less than 1.2%, with independent t-test showing insignificant bias. Two reference materials of human serum were analyzed, and our obtained values were compared with the reference values. The results showed very good precision with RSD around 0.2% and the deviation from the reference values were -3.1% and -2.1%. The newly developed method is precise, accurate, inexpensive, and environmentally friendly.
authors.affiliation: Chemical Metrology Laboratory, Applied Sciences Group, Health Sciences Authority, 1 Science Park Road, #01-05/06, The Capricorn, Singapore Science Park II, Singapore 117528, Singapore; Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore.
authors.forename: Sharon
authors.initials: S
authors.lastname: Yong
authors.affiliation: Chemical Metrology Laboratory, Applied Sciences Group, Health Sciences Authority, 1 Science Park Road, #01-05/06, The Capricorn, Singapore Science Park II, Singapore 117528, Singapore. Electronic address: chen_yizhao@hsa.gov.sg.
authors.forename: Yizhao
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Chemical Metrology Laboratory, Applied Sciences Group, Health Sciences Authority, 1 Science Park Road, #01-05/06, The Capricorn, Singapore Science Park II, Singapore 117528, Singapore.
authors.forename: Tong Kooi
authors.initials: TK
authors.lastname: Lee
authors.affiliation: Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore. Electronic address: chmleehk@nus.edu.sg.
authors.forename: Hian Kee
authors.initials: HK
authors.lastname: Lee
mesh_terms: D002138:Calibration; D002247:Carbon Isotopes; D002853:Chromatography, Liquid / Q000379:methods*; D006801:Humans; D059627:Liquid Phase Microextraction / Q000295:instrumentation / Q000379:methods*; D011126:Polypropylenes / Q000737:chemistry; D012016:Reference Values; D015203:Reproducibility of Results; D053719:Tandem Mass Spectrometry / Q000379:methods*; D013974:Thyroxine / Q000097:blood* / Q000302:isolation & purification
chemical_list: D002247:Carbon Isotopes; D011126:Polypropylenes; D013974:Thyroxine
keywords: Hollow fiber liquid-phase microextraction; Human serum; Liquid chromatography–tandem mass spectrometry; Total thyroxine