Mechanistic study of the sorption properties of OASIS® HLB and its use in solid-phase extraction

Summary The solvation parameter model is used to characterize the sorption properties of the porous polymer Oasis^? HLB for solid-phase extraction with water and water-methanol mixtures as a sample solvent. Increasing solute size and electron lone pair interactions favor retention from water. Oasis^? HLB is not competitive with water for dipole-type and hydrogen-bond interactions, which result in lower analyte retention. The selectivity of Oasis^? HLB is different to porous graphic carbon (Hypercarb^?), a conventional poly (styrene-divinylbenzene) porous polymer sorbent (PLRP-S 100) and two silica-based, octadecylsiloxane-bonded sorbents with a high and a low carbon loading, respectively. Because of selectivity differences no single sorbent is ideal for the extraction of analytes possessing a wide range of polar interactions. Oasis^? HLB is preferred for the extraction of low molecular mass and polar compounds, PLRP-S 100 for the extraction of higher molecular mass compounds of moderate polarity, and the silica-based octadecylsiloxane sorbent with a high carbon loading is the best compromise for the extraction of compounds that cover a wide polarity range. For methanol-water mixtures as a sample solvent PLRP-S 100 is the best general choice with Oasis^? HLB preferred for the extraction of strong hydrogen-bond acids. Hypercarb^? is shown to have favorable retention properties for solid-phase extraction with the except for its low surface area.     

A critical comparison of projection microradiography and the 2X method

Summary It is shown that Cosslett's criticism on the 2X method is based partly on a misconception of the resolving power of the photographic film and partly on a fundamentally wrong comparison between projection and 2X method. A generally valid comparison is given for the cases where the resolving power is not limited by Fresnel diffraction. Finally it is shown that Fresnel fringes are smaller in the 2X method than in a comparable projection system.The authors wish to express their gratitude to Dr. J.Bouman for the discussions which contributed especially to § 2.     

The Drazin inverse and a spectral inequality of marcus,minc, and moyls

Some properties of the Drazin inverse of a square matrix are derived which, together with elementary divisor theory, are used to investigate a spectral inequality which relates the maximal eigenvalues of two nonnegative indecomposable matrices.     

40.81 eV photoelectron spectroscopy of the thallous halides

Photoelectron spectra (using 40.81 eV photons) of TlF, TlCl, TlBr and TlI are presented. Absolute binding energies of the outermost halogen np levels with respect to the vacuum level and the energy separations between the thallium 5d_5/2 level and the halogen np level are compared with the corresponding energies predicted using the Born model for ionic solids. The thallium ion ²D_5/2 and ²D_3/2 final states display a non-statistical branching ratio and this is explained in terms of the relative photoionization cross-sections of d_5/2 and d_3/2 electrons. Structure in the spectrum of TIF is interpreted in terms of molecular orbital-like states.     

Formation of pentafluorophenyldimethylsilylethers and their use in the gas chromatographic analysis of sterols.

The pentafluorophenyldimethylsilyl group is an excellent protecting group for steroid alcohols, giving volatile ethers, detectable at picogram levels in gas chromatography with an electron capture detector. By the use of five reagents, increasingly hindered hydroxyl groups can be protected, so that structural information about unidentified sterols can be obtained. Quantitative derivative formation for a wide range of hydroxyl groups is possible by selection of the correct reagent combination, without affecting unprotected enolizable ketones.