Versatile organic (fullerene)-inorganic (CdTe nanoparticle) nanoensembles

Novel organic (positively charged fullerene)-inorganic (negatively charged CdTe nanoparticle) nanoensembles were devised through electrostatic interactions and probed as versatile donor-acceptor hybrids. Photoirradiation of their homogeneous solutions, containing the electrostatically packed components, let to very long-lived (1.3 ms) charge separated states.     

Effect of the Coil Angle in an Inductively Coupled Plasma Torch: A Novel Two-Dimensional Model

A two-dimensional model has been developed for the calculation of the electromagnetic (EM) fields generated by spiral coil currents, in order to obtain a better representation of the actual configuration used in a typical inductively coupled plasma (ICP) torch. In order to obtain the EM fields in a two-dimensional model, the change of EM field in tangential direction is neglected and the coil is assumed to be a concentric cylinder. In order to justify our assumption, the EM, flow and temperature fields resulting from five-ring coil and concentric cylinder coil are compared and the results are almost the same except for the EM field in the vicinity of the coil. In the case of the spiral coil, the coil current is inclined with respect to the horizontal plane. Therefore current in the cylinder coil is assumed to have the same inclined angle, which is split into tangential and axial components. The axial electric field and hence an axial current in plasma is induced by the axial component of the spiral coil current. Charge density is accumulated in the plasma, since the axial current cannot form a loop. In order to obtain the EM field and the charge distribution in the plasma generated by the spiral coil, the equations of axial vector potential and electrostatic potential have been derived. Due to the swirling Lorentz force (J_z×B_r) an axisymmetrical swirling fluid model is used to simulate the plasma flow in an axisymetrical configuration. With an inclined angle of the coil current being 3.7° and the frequency being 3 MHz, computational results show that the swirling Lorentz force causes plasma swirling with a maximum speed of 3.41 m/s near the plasma center when the injected sheath gas and central gas are not swirling. In these conditions, the real and imaginary parts of the maximum electrostatic potential are 0.95 V and 1.66 V, respectively. When the electrostatic field is neglected, the swirling velocity of the plasma is 3.95 m/s.     

Determination of total arsenic by use of a zinc-column arsine generator

A method for the measurement of total arsenic in extracts of environmental materials is described. Arsenic is reduced to arsine with a zinc reductor column, the evolved arsine is decomposed in a heated carbon-tube furnace, and arsenic determined by measurement of its atomic-absorption at 193.7 nm. The detection limit is 0.002 mug/ml and the coefficient of variation is 1.4% at 0.01 mug/ml.     

A microwave-assisted sequential extraction of water and dilute acid soluble arsenic species from marine plant and animal tissues

This paper describes the use of dilute nitric acid for the extraction and quantification of arsenic species. A number of extractants (e.g. water, 1.5 M orthophosphoric acid, methanol-water and dilute nitric acid) were tested for the extraction of arsenic from marine biological samples, such as plants that have proved difficult to quantitatively extract. Dilute 2% (v/v) nitric acid was found to give the highest recoveries of arsenic overall and was chosen for further optimisation. The optimal extraction conditions for arsenic were 2% (v/v) HNO₃, 6 min⁻¹, 90 °C. Arsenic species were found to be stable under the optimised conditions with the exception of the arsenoriboses which degraded to a product eluting at the same retention time as glycerol arsenoribose. Good agreement was found between the 2% (v/v) HNO₃ extraction and the methanol-water extraction for the certified reference material DORM-2 (AB 17.1 and 16.2 μg g⁻¹, respectively, and TETRA 0.27 and 0.25 μg g⁻¹, respectively), which were in close agreement with the certified concentrations of AB 16.4 ± 1.1 μg g⁻¹ and TETRA 0.248 ± 0.054 μg g⁻¹.To preserve the integrity of arsenic species, a sequential extraction technique was developed where the previously methanol-water extracted pellet was further extracted with 2% (v/v) HNO₃ under the optimised conditions. Increases in arsenic recoveries between 13% and 36% were found and speciation of this faction revealed that only inorganic and simple methylated species were extracted.     

Development of a pulsed-laser,fiber-optic-based fluorimeter: determination of fluorescence decay times of polycyclic aromatic hydrocarbons in sea water

A fiber-optic-based system for remote measurement of time-resolved fluorescence emission spectra is described and characterized. A pulsed nitrogen laser is used to induce fluorescence and a time-gated, one-dimensional photodiode array is used to measure the decay of the fluorescence emission spectra. The results compare favorably with reported values for well characterized compounds having fluorescence decay times in the range 4–50 ns. The potential of using time-resolved fluorimetry (TRF) over fiber-optic cables as a means of improving the specificity of remote fluorescence determinations of spectrally similar polycyclic aromatic hydrocarbons in sea water is demonstrated.     

The design of boronic acid spectroscopic reporter compounds by taking advantage of the pK(a)-lowering effect of diol binding: nitrophenol-based color reporters for diols

The complex that forms between a boronic acid and a diol is often much more acidic than the starting boronic acid. In conditions where the solution pH is between the two pK(a) values, the boron atom will convert from a neutral trigonal form to an anionic tetrahedral form upon complexation. Such a change is likely to dramatically alter the electron density of neighboring groups. Utilizing this effect, we have designed and synthesized two nitrophenol-based boronic acid reporter compounds that change ionization states and therefore spectroscopic properties upon diol binding. Both compounds show significant UV changes upon addition of saccharides. For example, a blue shift of the absorption max from 373 to 332 nm was observed with the addition of D-fructose to 2-hydroxy-5-nitrophenylboronic acid at neutral pH. Such a reporter compound can be used as a recognition and signaling unit for the construction of polyboronic acid sensors for the selective and specific recognitions of saccharides of biological significance.     

Solochrome Violet R als Reagens zur spektrophotometrischen Bestimmung von Mikrogrammengen Molybd?n

Zusammenfassung In der vorliegenden Arbeit wird eine rasche und genaue spektrophotometrische Bestimmung von Mikrogrammengen MolybdÄn beschrieben. Als Reagens wird der Azofarbstoff Solochrome Violet R verwendet. Dieser bildet mit MolybdÄn in sehwach salzsaurem Medium einen rotgefÄrbten Komplex, der selbst bei Anwesenheit von ÄDTA bestÄndig ist. Dadurch ist es möglich, den störenden Einflu\ anderer Ionen, z. B. den des Zirkoniums, auszuschalten. Mit dieser Methode lassen sich noch 2,0 g MolybdÄn/10 ml Me\lösung mit relativ hoher Genauigkeit bestimmen.Wir danken Herrn Prof. Dr. F. Hecht für seine Unterstützung, die für das Zustandekommen dieser Arbeit von gro\em Nutzen war.     

Separation of thiosulfate and the polythionates in gold thiosulfate leach solutions by capillary electrophoresis

A technique for the separation of thiosulfate (S(2)O(3) (2-)), polythionates (S(x)O(6) (2-), x = 3 to 5) and the gold(I) thiosulfate complex (Au(S(2)O(3))(2) (3-)) using capillary electrophoresis with simultaneous UV detection at 195 and 214 nm is presented. The five species were separated in under 3 min with a total analysis time of 8 min, using an electrolyte containing 25 mM 2,2-bis(hydroxymethyl)-2,2',2"-nitrilotriethanol (bis-tris) adjusted to pH 6.0 with sulfuric acid and an applied voltage of -30 kV. While the gold(I) thiosulfate complex could be separated from the other analytes of interest under these conditions, the quantification of this complex was not possible due to inconsistent peak areas and peak splitting effects induced by the sulfur-oxygen species in the leach matrix. Detection limits calculated for 3s pressure injection at 50 mbar ranged between 0.5-2 microM. The method was linear over the ranges 40-8000, 10-2000, 10-2000, and 5-2000 microM for thiosulfate, trithionate, tetrathionate, and pentathionate, respectively. The technique was applied successfully to leach liquors containing 0.5 M ammonium thiosulfate, 2 M ammonia, 0.05 M copper sulfate and 20% w/v gold ore, diluted 1:100 prior to analysis.     

Effect of electrospray ionization conditions on low-energy tandem mass spectra of peptides

The effect of electrospray ionization (ESI) conditions on low-energy tandem mass spectra of peptides in the relative molecular mass range 400–1200 was examined. For singly charged peptide ions the source skimmer potential (which determines the degree of acceleration of the ions through the intermediate pressure region in the source) can strongly influence the extent of fragmentation observed in tandem mass spectra, especially at low collision energies. For each peptide there is an optimum skimmer potential which represents a balance between generating ions with sufficient internal energy for subsequent tandem mass spectrometric experiments and inducing the onset of other processes such as source fragmentation. The fragmentation which can be achieved in tandem mass spectra with high skimmer potentials differs from ESI source fragmentation for the same peptides. We have found that fragmentation in ESI mass spectra depends both on skimmer potential and on solvent pH, presumably because the latter determines the proportion of doubly charged species generated from a given peptide. Low-energy tandem mass spectra of peptides following ESI are equally as sensitive to peptide structure and the type of adduct studied (e.g. [M + H]⁺ vs. [M + NH₄]⁺) as tandem mass spectra obtained following older ionization methods such as fast atom bombardment.