We describe a sensitive and specific method for the measurement of buprenorphine in human plasma. The method involves a structural analog as an internal calibrator, careful control of pH during sample extraction to maximize drug recovery, and back-extraction into acid followed by reextraction to eliminate endogenous interferences. After evaporation, sample residues are derivatized with heptafluorobutyric anhydride and analyzed by separation on a fused-silica polymethylsiloxane capillary column and electron-capture detection. Calibration curves were linear in the ranges 0.1–2.0 μg/L and 2.0–20 μg/L, with within-run CVs of 9.7% at 0.1 μg/L to 5.0% at 20 μg/L, and total CVs of 15.9% at 0.1 μg/L to 6.5% at 10 μg/L. The limit of quantification was 0.1 μg/L. The method was utilized in studies to determine the absolute bioavailability of sublingual doses of 2 mg of buprenorphine in 1 mL of 300 mL/L ethanol and the bioequivalence of sublingual 8-mg tablet and 300 mL/L ethanol solution formulations.
The anisotropic scattering properties of a uniaxially oriented filament of an ethylene-tetrafluoroethylene (E-TFE) alternating copolymer have been investigated in order to determine the molecular conformation in ordered crystalline regions. Both a trans-planar and a 312-helical structure have been shown to be energetically possible in an isolated molecule and in this study the group theoretical analyses for these structures are presented. Comparison of these results with polarized Raman measurements indicates that the copolymer backbone crystallizes in predominantly a planar-zigzag structure. Observation of the low-frequency Raman-active longitudinal acoustical mode (LAM) and the correlation of its frequency position with the crystalline stem length obtained from SAXS and crystallinity measurements strongly support the trans-planar structure.
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