Ck. Vanpelt et al., QUANTITATIVE SUBFEMTOMOLE ANALYSIS OF ALPHA-TOCOPHEROL AN DEUTERATED ISOTOPOMERS IN PLASMA USING TABLETOP GC MS/MS/, Analytical chemistry (Washington), 70(20), 1998, pp. 4369-4375
A rapid, high-selectivity method with subfemtomole sensitivity is repo
rted for quantification of alpha-tocopherol in plasma-based gas chroma
tography/tandem mass spectrometry (GC/MS/MS) using a tabletop quadrupo
le ion trap mass spectrometer. Sample workup is rapid, consisting of p
rotein precipitation followed by liquid/liquid extraction and O-trimet
hylsilyl derivatization of alpha-tocopherol (alpha-T-TMS) and an inter
nal standard, 2,2,5,7,8-pentamethyl-6-chromanol (PC-TMS). Rudimentary
chromatography was carried out using an 8-m DB-5 capillary column resu
lting in an analyte retention time of 7.2 min. No interferences from t
he 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 f
g)of derivatized alpha-tocopherol in diluted plasma; <30 pL of plasma
is estimated to yield sufficient alpha-tocopherol for quantitative ana
lysis at typical concentrations found in humans. A calibration curve c
onstructed from National Institute of Standards and Technology serum s
tandards 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 excee
d 11.3% for three concentrations of quality control (QC) solutions. Th
e 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-d(6) and alpha-tocopherol-d(3) were obtain
ed for a catheterized pregnant ewe and her fetus who were simultaneous
ly given a bolus injection of alpha-tocopherol-d(6), to the ewe and al
pha-tocopherol-d(3) to the fetus. These data show that a tabletop GC i
on trap can determine alpha-TT-TMS and its isotopomers quantitatively
at high selectivity in a complex matrix.