Analysis of biogenic amines by solid-phase microextraction and high-performance liquid chromatography with electrochemical detection

We investigated the new solid-phase microextraction method by high-performance liquid chromatography with electrochemical detection for the analysis of biogenic amines. The Carbowax–Templated Resin 50 μm (purple) fibre coating offers good performances for dopamine and serotonin separation, i.e., good selectivity and high sensibility (0.1 μg l⁻¹). We also tested this fibre for biogenic amines quantification of rat striatum. The coating seems to be selective towards the amines and has low affinity for the metabolites, allowing a good separation and preventing drawbacks from the biological matrix. These first results obtained using this original separation method offer large perspectives of application to many biological samples.     

Structural disorder along the lithium diffusion pathway in cubically stabilized lithium manganese spinel: I. Synchrotron X-ray studies

Electron density distribution, EXAFS, and transmission electron microscope studies on stoichiometric Li(Mg_1/6Mn_11/6)O₄ have revealed that: (1) the structure is essentially of spinel-type with slight diffuse scattering, (2) the Li atoms are not all located at the ideal 8a site of the spinel structure, but are partially tetrahedrally distributed along the 8a-16c tie line, (3) the O atoms also exhibit a statistical distribution about their ideal positions and (4) the Mn 3d electrons are squeezed out toward the open space of the coordinating octahedra with D_3d distortion. The present results indicate the possible existence of many metastable Li positions in the structure, suggestive of complicated Li atom hopping routes in conjunction with a local distortion of neighboring atoms at least up to the second shell.     

Osmotically driven crystal morphogenesis: a general approach to the fabrication of micrometer-scale tubular architectures based on polyoxometalates

The process of osmotically driven crystal morphogenesis of polyoxometalate (POM)-based crystals is investigated, whereby the transformation results in the growth of micrometer-scale tubes 10-100 μm in diameter and many thousands of micrometers long. This process initiates when the crystals are immersed in aqueous solutions containing large cations and is governed by the solubility of the parent POM crystal. Evidence is presented that indicates the process is general to all types of POMs, with solubility of the parent crystal being the deciding parameter. A modular approach is adopted since different POM precursor crystals can form tubular architectures with a range of large cationic species, producing an ion-exchanged material that combines the large added cations and the large POM-based anions. It is also shown that the process of morphogenesis is electrostatically driven by the aggregation of anionic metal oxides with the dissolved cations. This leads to the formation of a semi-permeable membrane around the crystal. The osmotically driven ingress of water leads to an increase in pressure, and ultimately rupture of the membrane occurs, allowing a saturated solution of the POM to escape and leading to the formation of a "self-growing" microtube in the presence of the cation. It is demonstrated that the growth process is sustained by the osmotic pressure within the membrane surrounding the parent crystal, as tube growth ceases whenever this pressure is relieved. Not only is the potential of the modular approach revealed by the fact that the microtubes retain the properties of their component parts, but it is also possible to control the direction of growth and tube diameter. In addition, the solubility limits of tube growth are explored and translated into a predictive methodology for the fabrication of tubular architectures with predefined physical properties, opening the way for real applications.     

Teaching teachers mathematics through programming

There are two main arguments underlying the claims for the value of interactive computer programming used by students to model mathematical ideas. One is concerned with mathematical content, i.e. with mathematics as an object of study. The other is concerned with mathematical activity, i.e. doing mathematics, or ‘Mathematicking’ [1]. Both content and activity include processes and these provide the main links with programming. Examples of processes in the content of mathematics are addition, transformation and integration, and these can be described by instructions in a computer program. Examples of process in the activity are problem‐solving, proof generation and pattern finding which can be described by analogy to program building and debugging. We assess the arguments for programming, in relation to the training of teachers, and describe a pilot‐study in which student teachers with mathematical difficulties were taught the programming language LOGO. Observation of the students, learning the language and using it to manipulate computer models of mathematical ideas, which they had not understood previously, highlights both advantages and disadvantages in this approach. The problem of the representation of mathematical ideas within programming projects is discussed.