Evaluation and performance of desorption electrospray ionization using a triple quadrupole mass spectrometer for quantitation of pharmaceuticals in plasma

The present work describes the methodology and investigates the performance of desorption electrospray ionization (DESI) combined with a triple quadrupole mass spectrometer for the quantitation of small drug molecules in human plasma. Amoxepine, atenolol, carbamazepine, clozapine, prazosin, propranolol and verapamil were selected as target analytes while terfenadine was selected as the internal standard common to each of the analytes. Protein precipitation of human plasma using acetonitrile was utilized for all samples. Limits of detection were determined for all analytes in plasma and shown to be in the range 0.2–40 ng/mL. Quantitative analysis of amoxepine, prazosin and verapamil was performed over the range 20–7400 ng/mL and shown to be linear in all cases with R² >0.99. In most cases, the precision (relative standard deviation) and accuracy (relative error) of each method were less than or equal to 20%, respectively. The performance of the combined techniques made it possible to analyze each sample in 15 s illustrating DESI tandem mass spectrometry (MS/MS) as powerful tool for the quantitation of analytes in deproteinized human plasma. Copyright © 2010 John Wiley & Sons, Ltd.     

Capillary liquid chromatography of multiple peptides with on-line capillary electrophoresis immunoassay detection.

A competitive immunoassay for neuropeptide Y (NPY) based on capillary electrophoresis (CE) with laser-induced fluorescence detection was developed utilizing polyclonal antisera as the immunoreagent and fluorescein-labeled NPY as the tracer. The assay was performed with on-line mixing of reagents, automated injections, and a 3 s separation time. The assay had a detection limit of 850 pM. To detect NPY at lower concentrations, the assay was coupled on-line to reversed-phase capillary liquid chromatography (LC). In this arrangement, 5 microL samples were preconcentrated by capillary LC and eluted by a gradient of isopropanol-containing mobile phase. The resulting chromatographic peaks were monitored by the CE immunoassay. With preconcentration, the concentration detection limit was improved to 40 microM and NPY could be measured in push-pull perfusion samples collected from the paraventricular nucleus of freely moving rats. The technique was extended to simultaneous detection of NPY and glucagon secretion from islets of Langerhans.     

James Mills Peirce and the cult of quaternions

Quaternions furnish an example of the rise and fall in popularity of a mathematical theory. Without attempting to trace its mathematical and sociological causes, this note highlights some moments in the history, of this phenomenon, as well as some of the scientists involved, especially the neglected mathematician, James Mills Peirce.     

Electrical and structural properties of iron-doped β-alumina

β-alumina containing 50 w/o Fe exhibits high electronic conductivity when sintered in air but Mössbauer studies have shown the presence of Fe₃O₄. Single-phase β-alumina containing 50 w/o Fe could be prepared by sintering at 1400°C for 4–4.5 h followed by annealing at 1300°C for 96 h encapsulated with coarse β-alumina powder enriched with Na₂CO₃. Mössbauer spectroscopy indicated that all iron was present as Fe(III). Complex-plane impedance data showed a maximum bulk $\text{σ}{}_{\mathrm{25°C}}\text{= 5.56 × 10}{}^{-4}\text{(Ω cm)}{}^{-1}$ with little electronic conductivity. Reduction treatments on Fe-doped β-alumina utilizing H₂:N₂ gas were successful in producing a mixed conductor containing Fe(II) and Fe(III) but also produced a distorted β-alumina lattice. This material exhibited an electronic conductivity $\text{σ}{}_{\mathrm{e,25°C}}\text{= 2 × 10}{}^{-4}\text{(Ω cm)}{}^{-1}$ and a bulk ionic conductivity $\text{σ}{}_{\mathrm{b,25°C}}\text{= 1.35 × 10}{}^{-4}\text{(Ω cm)}{}^{-1}$.     

Dependence of optically oriented and detected electron spin resonance on donor concentration in n-GaAs

Electron spin resonance of donors in GaAs has been observed through optical orientation and detection of spins. GaAs samples doped below the metal-insulator transition were studied. The resonance linewidth increases as the concentration of donors is reduced, due to the dependence of the T₂^* spin lifetime on correlation effects between donor electrons. The linewidth of the lowest doped sample (3×10¹⁴ cm⁻³) corresponds to a T₂^* of 5 ns, which is the value predicted for electrons in the non-interacting, localized limit. The nuclei need to be simultaneously depolarized in order to make the electron resonance observable.     

Standardizing NAA of biological samples of varying size, shape and composition

Neutron activation allows the analysis of wet and dry biological tissues without sample preparation. To eliminate the need to prepare standards of each element to match each sample, we have standardized for a small number of typical sample types and irradiation and counting conditions. Then, for each sample analyzed, the concentration calculation includes corrections to the neutron flux and the counting efficiency, which depend on sample size and composition. The effects corrected include the neutron flux gradient in the irradiation site, the moderation of the neutrons with the hydrogen content of the sample and the variation of counting efficiency with sample volume. This revised version was published online in August 2006 with corrections to the Cover Date.