The use of emulsions for the determination of methylmercury and inorganic mercury in fish-eggs oil by cold vapor generation in a flow injection system with atomic absorption spectrometric detection

An on-line time based injection system used in conjunction with cold vapor generation atomic absorption spectrometry and microwave-aided oxidation with potassium persulfate has been developed for the determination of the different mercury species in fish-eggs oil samples. A three-phase surfactant-oil-water emulsion produced an advantageous flow when a peristaltic pump was used to introduce the highly viscous sample into the system. The optimum proportion of the oil-water mixture ratio was 2:3 v/v with a Tween 20 surfactant concentration in the emulsion of 0.008% v/v. Inorganic mercury was determined after reduction with sodium borohydride while total mercury was determined after an oxidation step with persulfate prior to the reduction step to elemental mercury with the same reducing agent. The difference between total and inorganic mercury determined the organomercury content in samples. A linear calibration graph was obtained in the range 0.1-20 micrograms l-1 of Hg2+ by injecting 0.7 ml of samples. The detection limits based on 3 sigma of the blank signals were 0.11 and 0.12 microgram l-1 for total and inorganic mercury, respectively. The relative standard deviation of ten independent measurements were 2.8 and 2.2% for 10 micrograms l-1 and 8.8 and 9.0% for 0.1 microgram l-1 amounts of total and inorganic mercury, respectively. The recoveries of 0.3, 0.6 and 8 micrograms l-1 of inorganic and organic mercury added to fish-eggs oil samples ranged from 93.0 to 94.8% and from 100 to 106%, respectively. Good agreement with those values obtained for total mercury content in real samples by electrothermal atomic absorption spectrometry was also obtained, differences between mean values were < 7%. With the proposed procedure, 22 proteropterous catfish-eggs oil samples from the northwestern coast of Venezuela were measured; while the organic mercury lay in the range 2.0 and 3.3 micrograms l-1, inorganic mercury was not detected.     

Synthesis and characterization of a new isocyanato carborane anion [7-OCN-7-CB10H12]; study on its reactivity toward amino containing compounds

The new isocyanato carborane anion, [7-OCN-7-CB₁₀H₁₂]⁻ was prepared by the reaction of 7-H₃N-7-CB₁₀H₁₂ with triphosgene in the presence of triethylamine. The structure of this compound was established by ¹H, ¹¹B and ¹³C NMR as well as IR spectroscopy. The reactivigty of this compound with a series of organic amines was investigated. The resulting ureas were obtained in good to excellent yields. This approach is suitable for development of compounds for use in tumor selective Boron Neutron Capture Therapy (BNCT).     

Analysis of promazines in bovine livers by high performance liquid chromatography with ultraviolet and fluorimetric detection

Fluorimetric and UV methods of detection for liquid chromatographic determination of phenothiazines (chlorpromazine, acetopromazine and propionylpromazine) were developed. The effects of several experimental parameters on the separation and the sensitivity of the methods were evaluated. The detection limits ranged from 31 to 350 ng ml⁻¹. Optimized methods were successfully applied to determination of the promazines in bovine liver samples.     

Evaluation of Ptitsyn-Eizner λ parameter in dilute solutions of poly(N-vinylcarbazole) and its variation in conformational transitions of poly(methyl methacrylate)

The Ptitsyn-Eizner λ flexibility parameter for poly(N-vinylcarbozole) solutions under theta conditions has been found to be 6.31, demonstrating the rigidity imparted to the polymer chain by the carbazole group. A study has been made of the variation of this parameter with solvent and temperature. A study has been made of the variation of λ in a conformational transition of poly(methyl methacrylate).     

Color Displays with Gel-Glass Dispersed Liquid Crystals

Liquid crystal microdroplets trapped into silica gel-glasses by sol-gel processes may be used for display applications. Gel-glass dispersed liquid crystals (GDLC) are switched between opaque and transparent states by applying external AC-voltage signals; no polarizers are required. The feasibility of applying these materials to colored displays has been explored. A comparative study of different dyes for GDLC color displays, which were either embedded in the sol-gel matrix or dissolved in the liquid crystal microdroplets is presented.     

Michael additions of benzoins versus Michael-Stetter additions of aldehydes

Triethylamine catalyzed Michael additions of benzoins to chalcone can prevail over the expected Michael-Stetter additions when certain thiazolium ion conjugate bases - prepared $\text{in situ}$ from the pertinent thiazolium salts and triethylamine- are used as catalysts.     

Corrected Debye-Hückel analysis of surface complexation; III. Spherical particle charging including ion condensation

Statistical mechanics has been used to derive a model for the charging of a spherical particle in a salt solution to complement our experimental studies and gain a deeper understanding of the processes involved in surface complexation. Our chosen model goes beyond the equilibrium constants and the Gouy-Chapmann theory currently used in surface complexation models. The proton adsorption is taken to occur at a harmonic potential well on the surface characterized by a frequency v and a well depth u(0). Outside the particle surface there is a capacitor layer of width w(c) which is impenetrable to the salt ions. The diffuse screening of the charged particle is described by a corrected Debye-Hückel analysis accounting for ion size in the ion-ion interactions. To account also for nonlinear electrostatic response a layer of condensed counterions has been introduced. The criterion for the onset of ion condensation is that the electrostatic field exceeds a linear response criterion. Ion size effects are accounted for in terms of hole-corrected electrostatic energies and excluded volume. The model has been applied to titrated surface charge data on goethite (alpha-FeOOH) at various background concentrations and good agreement between the experimental data and the model was obtained. Both the size of the screening ions and the central particle size were shown to be of importance for the surface charge.     

Alternative Synthesis of A C,C-Diacetylenic Phosphaalkene

Abstract

Bis(trimethylsilyl)-terminated C,C-diacetylenic phosphaalkene was prepared from Mes*PCl₂ and a propargylic Grignard reagent that in turn was formed from 3-bromo-1,5-bis(trimethylsilyl)penta-1,4-diyne and Rieke-Mg.     

Self‐Assembled Monolayers of Cucurbit[6]uril on a Gold Electrode for 4,4′‐Oxydianiline Determination. Analytical Application

Self‐assembled monolayers of cucurbit[6]uril (CB[6]) on a gold electrode have been used for 4,4′‐oxydialine (ODA) analysis. The formation of the supramolecular complex between ODA and CB[6] was used for the molecular selection and the electroanalytical determination of this analyte. In addition to this, all the parameters affecting the modification of the gold electrode and the determination of 4,4′‐oxydianiline were optimized by square wave voltammetry. Upon the electrode modification, pentanethiol was employed to fill up the exposed surface between CB[6] molecules. The calculated detection and determination limits were 0.06 µg mL^?1 and 0.19 µg mL^?1, respectively, with good accuracy and precision as shown by the calculated values for the relative error and relative standard deviation (E_r=0.1 % and RDS=2.9 %; n=10 ). Moreover, the developed methodology was successfully applied to the 4,4′‐oxydialine determination in real wastewaters and shoe‐dyeing samples.