Development of an Analytical Methodology for Quantification of Strong Acid in Diesel Oil

Many factors can affect the quality of diesel oil, in particular the degradation processes that are directly related to some organosulfur compounds. During the degradation process, these compounds are oxidized into their corresponding sulfonic acids, generating a strong acid content during the process. p‐Toluene sulfonic acid analysis was performed using the linear sweep voltammetry technique with a platinum ultramicroelectrode in aqueous solution containing 3 mol L^?1 potassium chloride. An extraction step was introduced prior to the voltammetric detection in order to avoid the adsorption of organic molecules, which inhibit the electrochemical response. The extraction step promoted the transference of sulfonic acid from the diesel oil to an aqueous phase. The method was accurate and reproducible, with detection and quantification limits of 5 ppm and 15 ppm, respectively. Recovery of sulfonic acid was around 90%.     

Self-assembled monolayer of nickel(II) complex and thiol on gold electrode for the determination of catechin

Self-assembled monolayers of a nickel(II) complex and 3-mercaptopropionic acid on a gold electrode were obtained for determination of catechin by square wave voltammetry. The complex [Ni^IIL] with L = [N-(methyl)-N′-(2-pyridylmethyl)-N,N′-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-1,3-propanediamine[nickel(II)] was synthesized and characterized by ¹H NMR, IR, and electronic spectroscopies and electrochemical methods. The optimized conditions obtained for the electrodes were 0.1 mol L⁻¹ phosphate buffer solution (pH 7.0), frequency of 80.0 Hz, pulse amplitude of 60.0 mV and scan increment of 10.0 mV. Under these optimum conditions, the resultant peak current on square wave voltammograms increases linearly with the concentration of catechin in the range of 3.31 × 10⁻⁶ to 2.53 × 10⁻⁵ mol L⁻¹ with detection limits of 8.26 × 10⁻⁷ mol L⁻¹. The relative standard deviation for a solution containing 1.61 × 10⁻⁵ mol L⁻¹ catechin solution was 2.45% for eight successive assays. The lifetime of the Ni(II) complex-SAM-Au electrode was investigated through testing every day over 4 weeks. The results showed apparent loss of activity after 20 days. The results obtained for catechin in green tea samples using the proposed sensor and those obtained by electrophoresis are in agreement at the 95% confidence level.     

A one-pot synthesis of imidazo[1,5-a]pyridines

A one-pot synthesis of imidazo[1,5-a]pyridines starting from a carboxylic acid and 2-methylaminopyridines allowing introduction of various substituents at the 1- and 3-positions is achieved using propane phosphoric acid anhydride in ethyl or n-butyl acetate at reflux.     

Covalent Immobilization of α-Galactosidase from <Emphasis Type="Italic">Penicillium griseoroseum</Emphasis> and its Application in Oligosaccharides Hydrolysis

Partially purified α-Galactosidase from Penicillium griseoroseum was immobilized onto modified silica using glutaraldehyde linkages. The effective activity of immobilized enzyme was 33%. Free and immobilized α-galactosidase showed optimal activity at 45 °C and pH values of 5 and 4, respectively. Immobilized α-galactosidase was more stable at higher temperatures and pH values. Immobilized α-galactosidase from P. griseoroseum maintained 100% activity after 24 h of incubation at 40 °C, while free enzyme showed only 32% activity under the same incubation conditions. Defatted soybean flour was treated with free and immobilized α-galactosidase in batch reactors. After 8 h of incubation, stachyose was completely hydrolyzed in both treatments. After 8 h of incubation, 39% and 70% of raffinose was hydrolyzed with free and immobilized α-galactosidase respectively. Immobilized α-galactosidase was reutilized eight times without any decrease in its activity.     

Production of a <Superscript>173</Superscript>Lu target for neutron capture cross section measurements

Lutetium has been used as a radiochemistry detector to measure neutron fluence in NTS tests. A measure of the neutron capture cross sections on ¹⁷³Lu is needed to improve the interpretation value of the Lu radiochemistry isotopic ratios. A natural hafnium target was irradiated with protons to produce neutron poor lutetium radioisotopes. The short lived species were allowed to decay prior to chemical processing resulting in predominantly ¹⁷³Lu with a small amount of ¹⁷⁴Lu. This material was deposited on a titanium foil for use in the neutron capture cross section measurement.     

A comparative study of diffusion samplers for the determination of hexavalent chromium by sequential injection spectrophotometry

A method is described for determining hexavalent chromium in high particulate-containing surface waters by sequential injection (SI). The relative performance of two membrane-based methods for sampling is compared. The first membrane approach is based on a commercial design known as the ‘supported capillary membrane sampler (SCMS)’ (Wolcott, D.K., US Pat. 5 317 932 (1995)) that uses tubular membranes; the second approach is based on a conventional parallel-plate dialyzer (PPD) design that uses planar membranes. The membranes are evaluated using the well-known colorimetric method for the determination of hexavalent chromium by complexation with 1,5-diphenylcarbazide (DPC). Thin-walled (∼200 μm) microporous (pore size ∼0.2 μm) polypropylene membranes are equilibrated with DPC during each sampling period. Formation of the DPC-Cr(VI) complex allows for efficient membrane transport; without the membrane, Cr(VI) transport decreases ∼90%. Factors optimized included reagent concentrations, sampling time, flow rate, and spectrophotometric conditions. Optimal conditions were 2.00 mM DPC and 0.100 M nitric acid for the reagent, and 600 and 900 s sampling times for the planar and tubular designs, respectively. The planar (PPD) design increased the sensitivity relative to the tubular (SCMS) design by ∼225%. The PPD-SI method was applied to the determination of dissolved Cr(VI) in high particulate-containing surface water samples. Figures of merit included a detection limit of <20 μg/l, precision of 1.1% R.S.D. at 100 μg/l (n=4), and selectivity for dissolved Cr(VI) in several surface water samples with high levels of particulate matter.     

The Kernel of the Adjacency Matrix of a Rectangular Mesh

   Abstract. Given an m × n rectangular mesh, its adjacency matrix A , having only integer entries, may be interpreted as a map between vector spaces over an arbitrary field K . We describe the kernel of A : it is a direct sum of two natural subspaces whose dimensions are equal to

On the influence of laryngeal pathologies on acoustic and electroglottographic jitter measures

This study compared acoustic and electroglottographic (EGG) jitter from [a] vowels of 103 dysphonic speakers. The EGG recordings were chosen according to their intensity, signal-to-noise ratio, and percentage of unvoiced intervals, while acoustic signals were selected based on voicing detection and the reliability of jitter extraction. The agreement between jitter measures was expressed numerically as a normalized difference. In 63.1% (65/103) of the cases the differences fell within +/-22.5%. Positive differences above +22.5% were associated with increased acoustic jitter and occurred in 12.6% (13/103) of the speakers. These were, typically, cases of small nodular lesions without problems in the posterior larynx. On the other hand, substantial rises in EGG jitter leading to differences below -22.5% took place in 24.3% (25/103) of the speakers and were related to hyperfunctional voices, creaky-like voices, small laryngeal asymmetries affecting the arytenoids, or small-to-moderate glottal chinks. A clinically relevant outcome of the study was the possibility of detecting gentle laryngeal asymmetries among cases of large unilateral increase in EGG jitter. These asymmetries can be linked with vocal problems that are often overlooked in endoscopic examinations.     

Positivity of quasilocal mass

Motivated by the important work of Brown and York on quasilocal energy, we propose definitions of quasilocal energy and momentum surface energy of a spacelike 2-surface with a positive intrinsic curvature in a spacetime. We show that the quasilocal energy of the boundary of a compact spacelike hypersurface which satisfies the local energy condition is strictly positive unless the spacetime is flat along the spacelike hypersurface.     

Capture of Ni(II), Cu(I) and Z(II) by thiolate sulfurs of an N2S2Ni complex: a role for a metallothiolate ligand in the acetyl-coenzyme A synthase active site

The metal binding affinity of an (N2S2)Ni bridging metallothiolate ligand (Zn2+ < Ni2+ < Cu+) gives precedent for the observed heterogeneity in ACS/CODH.