R. Cela

Analytical applications of some flotation techniques-a review.

A review is given of the principles and more recent applications of foam flotation.

Simultaneous separation of copper, cadmium and cobalt from sea-water by co-flotation with octadecylamine and ferric hydroxide as collectors.

A method is proposed for the simultaneous quantitative separation of traces ofCu(II), Cd(II) and Co(II) from sea-water samples by means of the co-flotation (adsorbing colloid flotation) technique with ferric hydroxide as co-precipitant and octadecylamine as collector. The experimental parameters have been studied and optimized. The drawbacks arising from the low solubility of octadecylamine and the corresponding sublates in water have been avoided by use of a 6M hydrochloric acid-MIBK-ethanol (1:2:2 v v ) mixture. The results obtained by means of the proposed method have been compared with those given by the usual ammonium pyrrolidine dithiocarbamate/MIBK extraction method.

The preopt package for pre-optimization of gradient elutions in high-performance liquid chromatography

Abstract A theoretical model is described for quick pre-optimization of binary multistep gradient elutions in liquid chromatography. This model utilizes experimental retention-time data under isocratic elution conditions for different proportions of organic modifier in the mobile phase, and simulates the position of the peaks in the chromatogram by calculation of the average velocity of the peaks through the column. Optimization is done for multistep gradients by means of the simplex algorithm. The results must then be confirmed experimentally. Results are given demonstrating the power and validity of the model in the resolution of complex mixtures. The whole process done on a micro-computer with the PREOPT package usually takes about 30 min, without requiring user participation or chromatographic instrumentation.

Determination of Mo(VI) in tap-water and sea-water by differential-pulse polarography and co-flotation.

A new method is described for the microdetermination of Mo(VI) in natural waters and sea-water by differential-pulse polarography based on the catalytic wave caused by Mo(VI) in nitrate medium following preconcentration by co-flotation on Fe(III) hydroxide. In the case of sea-water samples, hexadecyltrimethylammonium bromide (HTAB) was used together with octadecylamine as the surfactant. For the analysis of natural water samples only HTAB is needed. Molybdenum in the range 0.7-5.7 ng/ml has been determined.

Preconcentration and determination of trace metals in synthetic sea water by flotation with inert organic collectors

Abstract The preconcentration and separation of copper, cadmium, cobalt and nickel 8-quinolinolates in solutions of high salinity including synthetic sea water is studied with phenolphthalein or 2-naphthol as collector and octadecylamine as surfactant. A simplex optimization is applied. Yields > 90% are achieved for Ni, Co and Cd with both collectors, but the copper yield is low. Flame atomic absorption spectrometry is used for the final measurements.

Studies on the browning of fino sherry and its relation to polyphenolic compounds

ZusammenfassungEs wurde der Gehalt der Gesamtpolyphenole mit der Jerumanis-Methode (einschließlich der phenolischen Säuren und Aldehyde unter Verwendung der HPLC-Technik) und deren Beziehung zum Braunwerden von Jerez Sherry verfolgt. Die Ergebnisse wurden mit der in der Literatur vorgeschlagenen Technik des beschleunigten Braunwerdens (Sauerstoffsättigung und mehrtägiges Erhitzen auf 50 °C) und dem Braunwerden in natürlicher Weise in der Flasche verglichen. Es konnte bewiesen werden, daß beschleunigtes Braunwerden kein guter Ersatz für das natürliche Braunwerden („remontado”) des feinen Sherryweines ist. Verschiedene Resultate gegenüber natürlich braungewordenem Sherry bestätigen dies.SummaryThe contents of total polyphenols (using the Jerumanis method) as well as phenolic acids and aldehydes (using highperformance liquid chromatography) and their relationship to the browning of Jerez sherry were studied. The results were compared with the accelerated browning process (oxygen saturation and heating at 50° C for several days), which appears commonly in the bibliography, and the natural browning process (which occurs naturally in the bottle). It was shown that the accelerated browning process cannot be used to stimulate the natural browning phenomenon (“remontado”) of fino sherry, as different results were obtained.

Influence of temperature in reverse-phase high-performance liquid chromatography with gradient elution

Abstract The influence of temperature on the retention of several species separated by reverse-phase liquid chromatography by gradient elution is shown to be of enough importance to warrant careful control of temperature if reproducible results are to be obtained. The smaller the particle size in the column, the greater the effect of temperature, and therefore the control should be greater. Likewise, it has been verified that for a given solvent gradient, independent of its complexity, there is a linear relation between ln k′ and 1/T, which also occurs in separations by isocratic elution. Dufeks equation can be adjusted perfectly to the experimental data obtained from gradient elutions, and may be used in the simulation and optimization of gradient chromatographic processes.

Solvent sublation of some priority pollutants (phenols)

Abstract Results are presented on the development of a new procedure for the preconcentration and analysis of the eleven phenolic compounds covered by the E.P.A. 604 method. This new procedure is applied to synthetic sea water samples, previously adjusted to pH 2, using stearylamine and hexadecyltrimethylammonium bromide as surfactants and concentrating the pollutants in a small volume of di-isopropyl-ether. Experimental conditions have been optimized by means of a procedure previously published by the authors, that makes use of the simplex algorithm. Under the final conditions established recoveries for the investigated compounds range within 80–95 %, except for phenol, only 60 % of which is recovered.