Enhanced conductometric detection of cyanide in suppressed ion chromatography

Weak-acid anions such as borate and cyanide, present problems in chemically suppressed ion chromatography, since the acids are weakly ionised, giving low conductivity and therefore decreased sensitivity. For borate this problem was overcome by converting the weak acid to its sodium salt, by the use of a second anion micromembrane suppressor (AMMS) as an ion exchange reactor (IER), flushed by EDTA reagent, to supply sodium ions for the conversion. This paper will discuss the use of this IER system to determine cyanide, which is also a very weak acid, with a similar pKa to borate. The detection limit for cyanide of 50 microM compare favourably with indirect conductivity detection.     

Magnetic resonance imaging in a model of atherosclerosis: use of a collar around the rabbit carotid artery

Transverse cardiac-cycle gated high resolution magnetic resonance images have been obtained from the neck of the New Zealand white rabbit both in normal animals and from those in which a collar had been earlier positioned around one carotid artery. The study included animals fed on normal and on high cholesterol diets with the surgical modification having been demonstrated previously to cause a rapid and reproducible lesion resembling early atherosclerosis. The aim of the work was to investigate the attainable spatial resolution and sensitivity at a field strength of 2 T using a large radiofrequency transmitter system and a surface coil receiver with which spin-echo images have been obtained. Visualization was enhanced using a three-dimensional interpolation technique. An image resolution of 200 microns was readily obtained but was shown to be insufficient for delineating pathological features within the artery wall such as intimal layer thickening. The results have been compared with histopathological findings which confirmed that any morphological changes were within the pixel resolution of the image. Extensions to the methodology are proposed which should be able to detect atherosclerotic changes with a resolution of 50 microns within a feasible imaging time. In addition, the MRI study of how the surgical intervention alters the artery shape and curvature was carried out and the MRI demonstrated that collar implantation in general does not occlude the artery and causes only a slight and gradual degree of curvature to the vessel.     

A method to enhance porosity of micro-particles

The nuclear track technique (NTT) is used to enhance the porosity of silica micro-particles. The enhanced porosity is a result of the formation of surface and interior pores or tracks in the silica by the action of external and internal fission fragments. The fission tracks produced at the surface and within the interior of the micro-particles are a result of coating the particles with trace quantitities of uranium, instead of having trace quantities of uranium incorporated within the silica matrix.     

The Ã1B2-X̃1A1 two-photon fluorescence excitation spectrum of 1,3-difluorobenzene

The $\text{A}\text{?}{}^1\text{B}{}_2\text{-}\text{X}\text{?}{}^1\text{A}{}_1$ system of 1,3-difluorobenzene has been observed using the technique of two-photon fluorescence excitation obtained with a pulsed dye laser. Calibration was achieved by a combination of the neon optogalvanic spectrum and etalon fringes. In circular, compared to linear, polarization the bands divide into two groups, those which are B₂-A₁ and which retain their intensity with circular polarization, and those which are A₁-A₁ and lose about 60% of their intensity under the same conditions. These two kinds of bands also show characteristic rotational contours. All of the A₁-A₁ bands whose assignments are established obtain their intensity through vibronic interaction in which the vibration ν′₂₅ (ν′₁₄ in the Wilson numbering) mixes the $\text{A}\text{?}$ with, presumably, the $\text{X}\text{?}$ state. There is an important Fermi resonance between the 9¹ and 10¹11¹ levels. Parts of the one-photon absorption spectrum have been photographed to identify sequences associated with the 0₀⁰ band for comparison with those observed in the two-photon spectrum, and to search for bands involving odd quanta of b₂ vibrations, including ν′₂₅ (ν′₁₄); none was found.     

Mapping of the cerebral response to acetazolamide using graded asymmetric spin echo EPI

Cerebral vascular reactivity in different regions of the rat brain was quantitatively characterized by spatial and temporal measurements of blood oxygenation level-dependent (BOLD)-fMRI signals following intravenous administration of the carbonic anhydrase inhibitor acetazolamide: this causes cerebral vasodilatation through a cerebral extracellular acidosis that spares neuronal metabolism and vascular smooth muscle function, thus separating vascular and cerebral metabolic events. An asymmetric spin echo-echo planar imaging (ASE-EPI) pulse sequence sensitised images selectively to oxygenation changes in the microvasculature; use of a surface coil receiver enhanced image signal-to-noise ratios (SNRs). Image SNRs and hardware integrity were verified by incorporating quality assurance procedures; cardiorespiratory stability in the physiological preparations were monitored and maintained through the duration of the experiments. These conditions made it possible to apply BOLD contrast fMRI to map regional changes in cerebral perfusion in response to acetazolamide administration. Thus, fMRI findings demonstrated cerebral responses to acetazolamide that directly paralleled the known physiological actions of acetazolamide and whose time courses were similar through all regions of interest, consistent with acetazolamide's initial distribution in brain plasma, where it affects cerebral haemodynamics by acting at cerebral capillary endothelial cells. However, marked variations in the magnitude of the responses suggested relative perfusion deficits in the hippocampus and white matter regions correlating well with their relatively low vascularity and the known vulnerability of the hippocampus to ischaemic damage.     

Synthesis and characterization of seven-coordinate tripodal imidazole complexes of iron(II) and manganese(II)

The iron(II) and manganese(II) complexes of the N(7) Schiff-base condensate of tris(3-aminopropyl)amine with 1-methyl-2-imidazolecarbaldehyde and the manganese(II) complex of the N(7) Schiff-base condensate of tris(3-aminopropyl)amine with 4-imidazolecarbaldehyde are high-spin mono capped octahedral seven-coordinate complexes with a short, approximately 2.44 è, metal to apical nitrogen bond.     

Level structure of 22Mg: implications for the 21Na(p,gamma)22Mg astrophysical reaction rate and for the 22Mg Mass

The level structure of (22)Mg has been studied with high-sensitivity gamma-ray spectroscopy techniques. A complete level scheme is derived incorporating all subthreshold states and all levels in the energy region relevant for novae burning. The excitation energy of the most important astrophysical resonance is measured with improved accuracy and found to differ from previous values. Combining the present result with a recent resonance energy measurement of this state leads to a derived (22)Mg mass excess of -400.5(13) keV.