Capillary-channeled polymer fibers as stationary phases in liquid chromatography separations

A method utilizing capillary-channeled polymer (C-CP) fibers as stationary phases in high-performance liquid chromatographic separations has been investigated. Polymeric fibers of differing backbones (polypropylene and polyester) having nominal diameters of approximately 50 and approximately 35 microm and a channeled structure on their periphery were packed into stainless steel tubing (305 x 4.6 mm I.D.) for use in reversed-phase separations of various mixtures. The fibers have eight channels running continuously along the axis which exhibit very high surface activity. As such, solvent transport is affected through the channels through wicking action. Bundles of 1000-3000 fibers are loaded co-linearly into the tubing, providing flow channels extending the entire length of the columns. As a result, backing pressures are significantly lowered (approximately 50% reduction) in comparison to packed-sphere columns. In addition, the capital costs of the fiber material (< US$0.25 per column) are very attractive. Flow-rates of up to 5 ml/min can be used to achieve near baseline separation of related compounds in reasonable run times, indicating very fast mobile phase mass transfer (C-terms). The polymer stationary phases demonstrate high selectivity for a wide variety of analytes with gradient elution employed successfully in many instances. Specifically, separations of three polyaromatic hydrocarbons (benzo[a]pyrene, chrysene, pyrene), mixtures of both organic and inorganic lead compounds [chlorotriethyllead, chlorotriphenyllead, lead nitrate, lead(II) phthalocyanine], and a lipid standard of triglycerides were accomplished on the polymeric stationary phases. Other species of biological interest, including groups of aliphatic and aromatic amino acids have also been effectively separated. The reversed-phase nature of the fiber surfaces is supported through atomic force microscopy measurements using hydrophilic and hydrophobic functionalized polystyrene beads as the probe tips. Separations of the various analytes demonstrate the feasibility of utilizing C-CP fibers as stationary phases in reversed-phase LC. It is envisioned that columns of this nature would be particularly useful in prep-scale separations as well as for immobilization matrices for organic constituents in aqueous environments.     

Rapid method for 226Ra and 228Ra analysis in water samples

Summary The measurement of radium isotopes in natural waters is important for oceanographic studies and for public health reasons. Radium-226 (T_1/2 = 1620 y) is one of the most toxic of the long-lived alpha-emitters present in the environment due to its long life and its tendency to concentrate in bones, which increases the internal radiation dose of individuals. The analysis of ²²⁶Ra and ²²⁸Ra in natural waters can be tedious and time-consuming. Different sample preparation methods are often required to prepare ²²⁶Ra and ²²⁸Ra for separate analyses. A rapid method has been developed at the Savannah River Environmental Laboratory that effectively separates both ²²⁶Ra and ²²⁸Ra (via ²²⁸Ac) for assay. This method uses MnO₂ Resin from Eichrom Technologies (Darien, IL, USA) to preconcentrate ²²⁶Ra and ²²⁸Ra rapidly from water samples, along with ¹³³Ba tracer. DGA Resin^ò (Eichrom) and Ln-Resin^ò (Eichrom) are employed in tandem to prepare ²²⁶Ra for assay by alpha-spectrometry and to determine ²²⁸Ra via the measurement of ²²⁸Ac by gas proportional counting. After preconcentration, the manganese dioxide is dissolved from the resin and passed through stacked Ln-Resin-DGA Resin cartridges that remove uranium and thorium interferences and retain ²²⁸Ac on DGA Resin. The eluate that passed through this column is evaporated, redissolved in a lower acidity and passed through Ln-Resin again to further remove interferences before performing a barium sulfate microprecipitation. The ²²⁸Ac is stripped from the resin, collected using cerium fluoride microprecipitation and counted by gas proportional counting. By using vacuum box cartridge technology with rapid flow rates, sample preparation time is minimized.     

TECRA Unique test for rapid detection of Salmonella in food: collaborative study

The TECRA Unique Salmonella test uses the principle of immunoenrichment to allow rapid detection of Salmonellae in food. A collaborative study was conducted to compare the TECRA Salmonella Unique test with the reference culture method given in the U.S. Food and Drug Administration's Bacteriological Analytical Manual. Three food types (milk powder, pepper, and soy flour) were analyzed in Australia and 2 food types (milk chocolate and dried egg) were analyzed in the United States. Forty-one collaborators participated in the study. For each of the 5 foods at each of the 3 levels, a comparison showed no significant differences (p > or = 0.05) in the proportion of positive test samples for Unique and that for the reference method using the Chi-square test for independence with continuity correction.     

Organogermanium compounds : XII. The stereochemistry of the reactions between optically active ethyl(1-naphthyl)phenylgermyllithium and alkyl halides

The interaction of optically active ethyl(1-naphthyl)phenylgermyllithium, R′₃-Ge*Li, with alkyl halides, RX, to give optically active R′₃Ge*R compounds, occurs with predominant retention of configuration at germanium in the case of MeBr, i-PrCl, i-PrBr, n-BuCl, n-BuBr, t-BuCl, t-BuBr, CH₂CHCH₂Cl, CH₂CHCH₂Br and PhCH₂Cl, but with predominant inversion in the case of MeI, i-PrI, CH₂CHCH₂I, PhCH₂I, and PhCH₂Br. It is suggested that the retention reactions involve direct coupling between R′₃Ge*Li and RX, in a four-centre process, while the inversion reactions involve halogen—lithium exchange, to give R′₃GeX and RLi, also in a four-centre retentive process, followed by coupling between R′₃GeX and RLi in an invertive process.     

Separation of sodiated isobaric disaccharides and trisaccharides using electrospray ionization-atmospheric pressure ion mobility-time of flight mass spectrometry

A series of isobaric disaccharide-alditols, four derived from O-linked glycoproteins, and select trisaccharides were rapidly resolved using tandem high resolution atmospheric pressure ion-mobility time-of-flight mass spectrometry. Electrospray ionization was used to create the gas-phase sodium adducts of each carbohydrate. Using this technique it was possible to separate up to three isobaric disaccharide alditols and three trisaccharides in the gas phase. Reduced mobility values and experimentally determined ion-neutral cross sections are reported for each sodium-carbohydrate complex. These studies demonstrated that ion mobility separations at atmospheric pressure can provide a high-resolution dimension for analysis of carbohydrate ions that is complementary to traditional mass spectral (m/z) ion analysis. Combining these independent principles for separation of ions provides a powerful new bioanalytical tool for the identification of isomeric carbohydrates.     

Comparison of thermal characteristics of materials examined by thermogravimetry and flammability tests

This paper deals with the examination of various types of flame resistant fabric in fire conditions, standard flammability tests and thermogravimetry. It shows how it may be possible to determine the protection afforded by a garment using very small samples and instrumental laboratory techniques. This could be important in the development of new materials where a quick assessment could be made of the protective qualities of the material.

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Zusammenfassung Es wird die Prüfung verschiedener feuerfester Gewebe unter Feuerbedingungen bei standardisierten Entzündbarkeitsprüfungen und durch Thermogravimetrie beschrieben. Es wird gezeigt, wie der durch ein Kleidungsstück gewährleistete Schutz mit sehr kleinen Proben und durch Laboratoriumstechnik bestimmt werden kann. Dies könnte bei der Entwicklung neuer Materialien von Wichtigkeit sein, wo eine Schnellbestimmung der Schutzeigenschaften des Materials durchgeführt werden muß.

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Résumé On examine différents types d'étoffes ignifuges du point de vue de l'inflammabilité et par thermogravimétrie. On montre la possibilité de déterminer à l'aide des techniques instrumentales de laboratoire, l'action protectrice d'un vêtement en utilisant de très petits échantillons. Cela pourrait être important lors du développement de matériaux nouveaux oú l'on pourrait soumettre à analyse rapide les qualités protectrices des étoffes.

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We wish to express our thanks to the Air Force Materials Laboratory, Air Force Systems Command, U.S. Air Force for the sample of PBI and to the Council and Director of LIRA for their permission to publish this paper.     

Rapid separation of phenylthiohydantoin amino acids: ambient pressure ion-mobility mass spectrometry (IMMS)

An electrospray ionization (ESI) ambient pressure ion-mobility spectrometer (APIMS) interfaced to an orthogonal reflector time-of-flight mass spectrometer (TOFMS) was evaluated for the first time as a detector for the identification of phenylthiohydantoin (PTH)-derivatized amino acids, the final products in the Edman sequencing process of peptides and proteins. The drift and flight times of the twenty common PTH amino acids were characterized by a well-defined 2-D mobility/mass spectral pattern. The combination of mobility/mass modes of analysis gave rise to a unique trend-line formation for the series of PTH amino acids. In addition, each PTH amino acid had a unique reduced mobility constant K(o), thus enabling the differentiation of all the amino acid derivatives including the PTH-leucine and PTH-isoleucine isomers. More importantly it was shown that it was possible to resolve a complete reference mixture of PTH amino acids in a single experimental run in less than 1 min. Detection limits for the PTH amino acids were found to range from 1.04 to 3.52 ng; indicating that the limits of detection were less than 17.0 pmol for all of the PTH amino acids.     

A screened indicator of methyl orange with sulfonated copper phthalocyanine

Summary Copper phthalocyanine tetra sulfonate pottasium salt, has been found to be very useful as a screening-dye to improve methyl orange end-points.Mixtures of methyl orange and dye in varying proportions have been prepared and tested for their indicator-action. The transformation interval of the indicator is found to change as the concentration of the dye is varied in the mixture.The optimum concentration of the dye to be used with a certain amount of methyl orange is determined so as to give a mixed-indicator that functions most satisfactorily in all titrations where methyl orange is used.     

Directly visualizing carrier transport and recombination at individual defects within 2D semiconductors

Two-dimensional semiconductors (2DSCs) are promising materials for a wide range of optoelectronic applications. While the fabrication of 2DSCs with thicknesses down to the monolayer limit has been demonstrated through a variety of routes, a robust understanding of carrier transport within these materials is needed to guide the rational design of improved practical devices. In particular, the influence of different types of structural defects on transport is critical, but difficult to interrogate experimentally. Here, a new approach to visualizing carrier transport within 2DSCs, Carrier Generation-Tip Collection Scanning Electrochemical Cell Microscopy (CG-TC SECCM), is described which is capable of providing information at the single-defect level. In this approach, carriers are locally generated within a material using a focused light source and detected as they drive photoelectrochemical reactions at a spatially-offset electrolyte interface created through contact with a pipet-based probe, allowing carrier transport across well-defined, µm-scale paths within a material to be directly interrogated. The efficacy of this approach is demonstrated through studies of minority carrier transport within mechanically-exfoliated n-type WSe₂ nanosheets. CG-TC SECCM imaging experiments carried out within pristine basal planes revealed highly anisotropic hole transport, with in-plane and out-of-plane hole diffusion lengths of 2.8 µm and 5.8 nm, respectively. Experiments were also carried out to probe recombination across individual step edge defects within n-WSe₂ which suggest a significant surface charge (∼5 mC m⁻²) exists at these defects, significantly influencing carrier transport. Together, these studies demonstrate a powerful new approach to visualizing carrier transport and recombination within 2DSCs, down to the single-defect level.

Probe-based electrochemical techniques can be used to map carrier transport and recombination within two-dimensional semiconductors.     

Derivation of class II force fields. VIII. Derivation of a general quantum mechanical force field for organic compounds

A class II valence force field covering a broad range of organic molecules has been derived employing ab initio quantum mechanical "observables." The procedure includes selecting representative molecules and molecular structures, and systematically sampling their energy surfaces as described by energies and energy first and second derivatives with respect to molecular deformations. In this article the procedure for fitting the force field parameters to these energies and energy derivatives is briefly reviewed. The application of the methodology to the derivation of a class II quantum mechanical force field (QMFF) for 32 organic functional groups is then described. A training set of 400 molecules spanning the 32 functional groups was used to parameterize the force field. The molecular families comprising the functional groups and, within each family, the torsional angles used to sample different conformers, are described. The number of stationary points (equilibria and transition states) for these molecules is given for each functional group. This set contains 1324 stationary structures, with 718 minimum energy structures and 606 transition states. The quality of the fit to the quantum data is gauged based on the deviations between the ab initio and force field energies and energy derivatives. The accuracy with which the QMFF reproduces the ab initio molecular bond lengths, bond angles, torsional angles, vibrational frequencies, and conformational energies is then given for each functional group. Consistently good accuracy is found for these computed properties for the various types of molecules. This demonstrates that the methodology is broadly applicable for the derivation of force field parameters across widely differing types of molecular structures. Copyright 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1782-1800, 2001