title: A new method for immediate derivatization of hydroxyl groups by fluoroalkyl chloroformates and its application for the determination of sterols and tocopherols in human serum and amniotic fluid by gas chromatography-mass spectrometry.
abstract: A new method has been described for efficient derivatization of secondary alicyclic hydroxyl groups in steroids by alkyl chloroformates (RCFs). Cholesterol, an essential human sterol and a steroid precursor in eukaryotic cells, was used as a model for treatment with various RCFs in an aqueous and non-aqueous environment. While the cholesterol hydroxyl group did not react completely with any of the tested RCFs reagents in the former case, trifluoroethyl chloroformate (TFECF) or heptafluorobutyl chloroformate (HFBCF) fully converts cholesterol and related metabolites into the corresponding mixed carbonates under anhydrous conditions in seconds. The acylation reaction was combined with liquid-liquid microextraction (LLME) between isooctane and acetonitrile phase. The sample preparation requires just a stepwise addition of 50μl isooctane with 5μl of a pyridine catalyst, 100μl acetonitrile and 100μl isooctane with dissolved 5μl of the fluoroalkyl chloroformate reagent to a dried sample. The protocol developed in this study was successfully tested for GC-MS analysis of 12 important model steroids and four main tocopherols. Each analyte provided a single peak with excellent GC separation properties, well defined EI spectra containing diagnostic fragment ions suitable for their identification and quantitation. The new method was further validated for the determination of six diagnostic non-cholesterol sterols and four main tocopherols in human serum and in amniotic fluid. Satisfactory data were obtained in terms of calibration, quantitation limits (for sterols and tocopherols, 0.05 and 0.15μg/ml, respectively), within-run precision (0.9-19.5%) and between-run precision (0.2-19.0%), accuracy (82-115%) and recovery (90-110%). The validated method was successfully applied to GC-MS analysis of the analytes in woman sera and amniotic fluids and the results are well-comparable with those reported by other authors. The presented work demonstrates for the first time capability of the RCFs to derivatize alicyclic hydroxyls in steroids and tocopherols metabolites for GC-MS with excellent reaction rates, highest reaction yields, minor reagent consumption and easy conjunction with LLME methods.
authors.affiliation: Laboratory of Analytical Biochemistry, Institute of Entomology, Biology Centre, Academy of Sciences of the Czech Republic, Branišovská 31/1160, CZ-37005 České Budějovice, Czech Republic; Department of Analytical Chemistry, Faculty of Sciences, Charles University in Prague, Albertov 6, CZ-12840 Prague 2, Czech Republic.
authors.forename: L
authors.initials: L
authors.lastname: Řimnáčová
authors.affiliation: Laboratory of Analytical Biochemistry, Institute of Entomology, Biology Centre, Academy of Sciences of the Czech Republic, Branišovská 31/1160, CZ-37005 České Budějovice, Czech Republic.
authors.forename: P
authors.initials: P
authors.lastname: Hušek
authors.affiliation: Laboratory of Analytical Biochemistry, Institute of Entomology, Biology Centre, Academy of Sciences of the Czech Republic, Branišovská 31/1160, CZ-37005 České Budějovice, Czech Republic; Department of Laboratory Methods and Information Systems, Faculty of Social and Health Sciences, University of South Bohemia, J. Boreckého 27, CZ-370 11 České Budějovice, Czech Republic. Electronic address: psimek@bclab.eu.
authors.forename: P
authors.initials: P
authors.lastname: Šimek
mesh_terms: D000653:Amniotic Fluid / Q000737:chemistry*; D005260:Female; D005466:Fluorocarbons / Q000737:chemistry*; D005561:Formates / Q000737:chemistry*; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D007202:Indicators and Reagents; D059627:Liquid Phase Microextraction; D011247:Pregnancy; D044967:Serum; D013261:Sterols / Q000032:analysis* / Q000097:blood; D024505:Tocopherols / Q000032:analysis* / Q000097:blood
chemical_list: D005466:Fluorocarbons; D005561:Formates; D007202:Indicators and Reagents; D013261:Sterols; C570844:heptafluorobutyl chloroformate; D024505:Tocopherols
keywords: Alkyl chloroformate derivatization; Amniotic fluid; Gas chromatography–mass spectrometry; Human serum; Liquid–liquid microextraction; Steroid hydroxyl group