Evaluation of mass spectrometry and radiation detection for the analysis of radionuclides

Summary The feasibility of measuring picogram levels of actinides in a urine matrix using ion chromatography coupled on-line to an inductively coupled plasma quadrupole mass spectrometer (IC-Q-ICPMS) was investigated. A chelation column for separation of matrix ions and preconcentration of the actinides was combined with a cation-exchange column for separation of the actinides. Sample preparation required simple addition of ammonium acetate to adjust the pH of the urine matrix. Spike solutions containing ²³² Th, ²³⁷Np, ²³⁸U, ²³⁹Pu, and ²⁴¹Am were added to undiluted urine, diluted urine (1 : 9) and water. Results showed that this approach enhanced the signal sensitivities of all the tested actinides over two orders of magnitude in the water matrix, while certain elements (especially Am) can still be effectively concentrated in undiluted urine.     

Quantitation of small molecules using high‐resolution accurate mass spectrometers – a different approach for analysis of biological samples

The quantitative capabilities of a linear ion trap high‐resolution mass spectrometer (LTQ‐Orbitrap™) were investigated using full scan mode bracketing the m/z range of the ions of interest and utilizing a mass resolution (mass/FWHM) of 15000. Extracted ion chromatograms using a mass window of ±5–10 mmu centering on the theoretical m/z of each analyte were generated and used for quantitation. The quantitative performance of the LTQ‐Orbitrap™ was compared with that of a triple quadrupole (API 4000) operating using selected reaction monitoring (SRM) detection. Comparable assay precision, accuracy, linearity and sensitivity were observed for both approaches. The concentrations of actual study samples from 15 Merck drug candidates reported by the two methods were statistically equivalent. Unlike SRM being a tandem mass spectrometric (MS/MS)‐based detection method, a high resolution mass spectrometer operated in full scan does not need MS/MS optimization. This approach not only provides quantitative results for compounds of interest, but also will afford data on other analytes present in the sample. An example of the identification of a major circulating metabolite for a preclinical development study is demonstrated. Copyright © 2009 John Wiley & Sons, Ltd.     

Minimum thermal conductivity of superlattices

The phonon thermal conductivity of a multilayer is calculated for transport perpendicular to the layers. There is a crossover between particle transport for thick layers to wave transport for thin layers. The calculations show that the conductivity has a minimum value for a layer thickness somewhat smaller then the mean free path of the phonons.     

Covalent bonds in ionic crystals

An ion at a tetrahedral site will develop an induced octupole moment, which is equivalent to a covalent bond. The magnitude of this bond is calculated For AgI and the copper halides, and removes a discrepancy between theory and experiment which has stood for 47 years.     

Effects of adsorbates on electron spin polarization in low energy electron diffraction from tungsten (001): I. Disordered CO and O2 overlayers

Electron spin polarization and intensity profiles have been measured in low energy electron diffraction (LEED) for the (00) beam at θ = 13δ and ø = 0δ from W(001) as a function of surface exposure to CO and O₂. Significant changes have been observed in the profiles upon exposure to both adsorbate gases, and the implications of these results are discussed.     

The phonon spectra of the superionic conductor KBiF4 (a CaF2 Analogue)

Theoretical calculations of the phonon infrared and Raman response in simple superionic conductors such as AgI, CuI, and CaF₂ types are based on two fundamental assumptions. First, most of the response can be understood in terms of a breakdown of the selection rules due to disorder (lack of translational symmetry) and second, harmonic lattice dynamics can be used with a good degree of accuracy. This is tested here experimentally in the superionic conductor K_1?xBi_1+xF_4+2x which has the CaF₂ structure (x=0.0 is analogous to 2CaF₂). By varying x we increase the disorder (via F-ion interstitials and vacancies) and measure broad temperature independent reduced Raman and infrared responses. The broad response is dependent on x in a manner consistent with the first assumption and the lack of temperature dependence is consistent with the second assumption. In order to understand the transverse optic vibrational frequencies (ω_TO) we have found that plots of ω_TO²vs. μ^-1 (reduced mass) are very helpful. The linearity of such plots, for example, for tetrahedrally bonded AgI, CuI, CuBr, CuCl (formal charge Z=1) and the difference of such results for similar materials but with formal charges of 2, 3, and 4 is surprising and not as yet understood. Other conclusions are discussed at the end of the paper.     

Disorder and ionic polarons in solid electrolytes

The role of ion-ion repulsion and ion-phonon coupling in superionic conduction is explored. It is argued that the order-disorder phase transition is not associated with the conductivity discontinuity, but with a higher temperature second order phase transition which has been seen in some superionic conductors and which we predict for others. The specific heat, ion distribution, and conductivity are calculated.