title: Quantitative subfemtomole analysis of alpha-tocopherol and deuterated isotopomers in plasma using tabletop GC/MS/MS.
abstract: A rapid, high-selectivity method with subfemtomole sensitivity is reported for quantification of alpha-tocopherol in plasma-based gas chromatography/tandem mass spectrometry (GC/MS/MS) using a tabletop quadrupole ion trap mass spectrometer. Sample workup is rapid, consisting of protein precipitation followed by liquid/liquid extraction and O-trimethylsilyl derivatization of alpha-tocopherol (alpha-T-TMS) and an internal standard, 2,2,5,7,8-pentamethyl-6-chromanol (PC-TMS). Rudimentary chromatography was carried out using an 8-m DB-5 capillary column resulting in an analyte retention time of 7.2 min. No interferences from the plasma matrix were observed. The assay has a detection limit of 178 amol (89.6 fg) and a lower limit of quantification of 700 amol (350 fg) of derivatized alpha-tocopherol in diluted plasma; < 30 pL of plasma is estimated to yield sufficient alpha-tocopherol for quantitative analysis at typical concentrations found in humans. A calibration curve constructed from National Institute of Standards and Technology serum standards was linear in the working range of 1.9-1073 ng/mL (0.95-0.54 ng). Within- and between-day precision averaged 5.8% and did not exceed 11.3% for three concentrations of quality control (QC) solutions. The overall accuracy for the QC samples was within 7.2%. Storage studies showed that, alpha-T-TMS and PC-TMS are stable under conditions that might be encountered during analyses. In a test study, plasma kinetic curves for alpha-tocopherol-d6 and alpha-tocopherol-d3 were obtained for a catheterized pregnant ewe and her fetus who were simultaneously given a bolus injection of alpha-tocopherol-d6, to the ewe and alpha-tocopherol-d3 to the fetus. These data show that a tabletop GC ion trap can determine alpha-T-TMS and its isotopomers quantitatively at high selectivity in a complex matrix.
authors.affiliation: Division of Nutritional Sciences, Cornell University, Ithaca, New York 14853, USA.
authors.forename: C K
authors.initials: CK
authors.lastname: Van Pelt
authors.forename: P
authors.initials: P
authors.lastname: Haggarty
authors.forename: J T
authors.initials: JT
authors.lastname: Brenna
mesh_terms: D000818:Animals; D002839:Chromans / Q000097:blood; D003903:Deuterium; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D011247:Pregnancy; D012015:Reference Standards; D015203:Reproducibility of Results; D012756:Sheep; D014297:Trimethylsilyl Compounds; D014810:Vitamin E / Q000097:blood* / Q000592:standards
chemical_list: D002839:Chromans; D014297:Trimethylsilyl Compounds; D014810:Vitamin E; C029141:2,2,5,7,8-pentamethyl-1-hydroxychroman; D003903:Deuterium