A manifold for the automatic dilution of concentrated solutions in flame atomic absorption spectrometry

A fully computer-controlled manifold is described which enables the automatic dilution and measurement of solutions which are too concentrated to be measured by direct aspiration in FAAS. The sample solution is propelled by a peristaltic pump equipped with two pump tubes of different diameters, the difference between the nebulizer uptake rate and the flow rate supplied by both tubes being compensated by solvent provided through a T-piece. The absorbance is averaged and the pump turning speed automatically increased or reduced until an absorbance value within the linear response of the spectrometer is obtained. To furnish very high dilution, the system automatically reverses the direction of the flow moved through one of the pump tubes, so that the net flow delivered by the pump is the difference between the flows propelled through the two pump tubes. In these circumstances, in addition to absorbance, the module of the Fourier transform obtained from the absorbance-time profile can be used as the analytical signal. Calibration is performed by use of a single standard solution. In this way, it is possible to determine copper in the 1-10,000 microg mL(-1) range with an RSD of 1.3-3%. Copper, zinc, calcium, and magnesium were determined in different samples to check the reliability of the procedure.     

Comparison of HPLC and multivariate regression methods for hydrocortisone and lidocaine analysis of pharmaceutical preparations

A reverse-phase high-performance liquid chromatographic (HPLC) method to determine hydrocortisone acetate, hydrocortisone hemisuccinate and lidocaine is described in this paper. The separation was made in a LichrCART C(18) column using a methanol-NaH(2)PO(4)/Na(2)HPO(4) (0.1 mol L(-1)) (pH=4.5) buffer solution as a mobile phase in isocratic mode (60:40 (v/v)). The mobile phase flow rate and the sample volume injected were 1 mL min(-1) and 20 micro L, respectively. The detection was made with a diode-array detector measuring at the maximum for each compound. Quantification limits ranging from 0.18 to 0.84 micro g L(-1) were obtained when the peak area was measured. The method was applied in pharmaceutical formulations that were compared with those obtained by through multivariate regression spectrophotometry and micellar capillary electrophoresis (MEKC). HPLC results are in accordance with the results obtained by MEKC. The spectrophotometric method was suitable only for synthetic samples.     

Neutron-activation determination of vanadium in oils and catalysts

Summary Vanadium in crude and residual oils and in catalysts at the concentration levels of 0.2–200 and 400–2000 ppm respectively has been determined by means of neutron-activation analysis based on measurement of the nuclide⁵²V. The aim was to apply the technique to industrial or general routine analysis. Four samples were analysed simultaneously in less than 15 minutes.

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Zusammenfassung In Rohöl, Rückstandöl und in Katalysatoren wurde Vanadin in Konzentrationen von 0,2 bis 200 bzw. 400 bis 2000 ppm mit Hilfe der Neutronenaktivierungsanalyse bestimmt, indem das Nuklid⁵²V gemessen wurde. Die Absicht war, dieses Verfahren für industrielle Routineanalysen anzuwenden. In weniger als 15 Minuten lassen sich gleichzeitig vier Proben analysieren.

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Work supported under the International Atomic Energy Agency (IAEA) Technical Assistance Programme.     

Characterization of novel neopullulanase fromBacillus polymyxa

Bacillus polymyxa CECT 155 produces an extracellular neopullulanase activity that degrades pullulan to panose. This activity was stimulated by the presence of pullulan in the culture, and repressed by glucose. The apparent mol wt determined for the enzyme was 58 kDa. The optimum pH and temperature for neopullulanase activity were pH 6.0 and 50°C, respectively. The enzyme was stable in a pH range of 4.0–8.0, and temperatures up to 60°C. These properties make it suitable for the saccharification processes in the starch industries.     

Fluorothiolate–dithioacid complexes of ruthenium(III) and osmium(III): crystal structure of [Os(SC6F5)2(S2CNEt2)(PMe2Ph)2]

Treatment of the coordinative unsaturated complexes [M(SR_F)₃(PMe₂Ph)₂] (M = Os or Ru; R_F = C₆F₅ or C₆F₄H-4) with MS₂Z (M = Na, S₂Z = S₂CNEt₂; M = K, S₂Z = S₂COEt) and [Os(SR_F)₃(PMe₂Ph)₂] (R_F = C₆F₅ or C₆F₄H-4) with MS₂Z [M = Na; S₂Z = S₂P(OEt)₂] in Me₂CO solution, gave the paramagnetic Os^III and Ru^III derivatives, [M(SR_F)₂(S₂Z)(PMe₂Ph)₂]. X-ray crystallography shows that [Os(SC₆F₅)₂(S₂CNEt₂)(PMe₂Ph)₂] has an octahedral geometry with trans-fluorothiolates, cis-phosphines and a chelating N,N-diethyldithiocarbamate ligand.     

Measurement of the Low-Frequency Dielectric Properties of Colloidal Suspensions: Comparison between Different Methods

A careful analysis of the main factors that affect the low-frequency dielectric measurements of conducting liquid samples is carried out. The influence of the type of the measurement cell, the calibration method, and the type of the instrument used, on the spectra obtained using the variable electrode spacing technique, is investigated. Permittivity and conductivity measurements in the 10 Hz to 10 MHz range are reported for low (sigma approximately 0.01 S/m) and high (sigma approximately 0.7 S/m) conductivity samples, both electrolyte solutions and polystyrene particle suspensions. Two measurement cells are evaluated: one made of glass currently used at Granada and the other made of acrylic currently used at Tucumán. Two calibration methods, the classical Short/Open correction and the quadrupolar technique (similar to the Short/Open/Load correction), are contrasted, and two impedance analyzers, the HP 4284 A and the HP 4192 A, are compared. Copyright 2000 Academic Press.     

Accessible and Cost-Effective Method of PDMS Microdevices Fabrication Using a Reusable Photopolymer Mold

This work describes a novel and cost-effective method of polydimethylsiloxane (PDMS) microchips fabrication by using a printing plate photopolymer called Flexcel as a master mold (Fmold). This method has demonstrated the ability to generate multiple devices from a single master, reaching a minimum channel size of 25 μm, structures height ranging from 53 to 1500 μm and achieving dimensions of 1270 × 2062 mm², which are larger than those obtained by the known techniques to date. Scanning electron microscopy, atomic force microscopy, and profilometry techniques have been employed to characterize the Fmold and PDMS replicas. The results showed high replication fidelity of Fmold to the PDMS replica. Furthermore, it was proved the reusability of the Fmold. In our study, up to 50 PDMS replicas have been fabricated without apparent degradation of the mold. The feasibility of the resulting PDMS replica was effectively demonstrated using a microfluidic device for enhanced oil recovery analysis. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1433–1442     

A general view of pseudoharmonics and pseudoantiharmonics to calculate external arguments of Douady and Hubbard

Harmonics give us a compact formula and a powerful tool in order to calculate the external arguments of the last appearance hyperbolic components and Misiurewicz points of the Mandelbrot set in some particular cases. Antiharmonics seem however to have no application. In this paper, we give a general view of pseudoharmonics and pseudoantiharmonics, as a generalization of harmonics and antiharmonics. Pseudoharmonics turn out to be a more powerful tool than harmonics since they allow the calculation of external arguments of the Mandelbrot set in many more cases. Likewise, unlike antiharmonics, pseudoantiharmonics turn out to be a powerful tool to calculate external arguments of the Mandelbrot set in some cases.