A simple and rapid ultra-high-performance liquid chromatography-tandem mass spectrometry method to determine plasma biotin in hemodialysis patients.
A simple, rapid, and selective method for determination of plasma biotin was developed using ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). After single-step protein precipitation with methanol, biotin and stable isotope-labeled biotin as an internal standard (IS) were chromatographed on a pentafluorophenyl stationary-phase column (2.1 × 100 mm, 2.7 μm) under isocratic conditions using 10 mm ammonium formate-acetonitrile (93:7, v/v) at a flow rate of 0.6 mL/min. The total chromatographic runtime was 5 min for each injection. Detection was performed in a positive electrospray ionization mode by monitoring selected ion transitions at m/z 245.1/227.0 and 249.1/231.0 for biotin and the IS, respectively. The calibration curve was linear in the range of 0.05-2 ng/mL using 300 μL of plasma. The intra- and inter-day precisions were all <7.1%. The accuracy varied from -0.7 to 8.2%. The developed UHPLC-MS/MS method was successfully applied to determine plasma biotin concentrations in hemodialysis patients. Copyright © 2016 John Wiley & Sons, Ltd.
Biotin and biotin analogs in human urine: biotin accounts for only half of the total.
In studies using avidin-binding assays to measure the urinary excretion of biotin, biotin is sometimes assumed to be equal to the detectable avidin-binding substances present. High performance liquid chromatography was used to separate avidin-binding substances in human urine, and the chromatographic fractions were assayed for avidin-binding substances (biotin and biotin analogs) by a sensitive, specific assay based on binding of biotin to [125I]avidin. In a study of ten normal adults, substantial amounts of avidin-binding substances other than biotin were detected, two of which were bisnorbiotin and biotin sulfoxide. These biotin analogs were initially identified by their chromatographic properties, and identities were confirmed by chemical conversion. The presence of avidin-binding substances in addition to biotin may have confounded previous measurements of the urinary excretion of biotin using avidin-binding assays. Because bioassay methods for biotin often use organisms for which one or more of these biotin analogs are growth factors, measurements of biotin in urine using some bioassay methods are likely to overestimate the concentrations of biotin.
An Essay on the Nature and Significance of the Normative Nature of Economics
It is conventional in economics to distinguish between the normative and the positive. The normative has to do with goodness and badness, and with what ought and ought not to be done;1 and the positive has to do with objective description and/or explanation, with what is and with what is necessary given some normative end. The normative has to do with desirability; the positive has to do with truth (in the sense of either descriptive accuracy or serviceability of a means to a given end).2