M. P. San Andrés

Spectrophotometric determination of copper(II), nickel(II) and cobalt(II) as complexes with sodium diethyldithiocarbamate in cationic micellar medium of hexadecyltrimethylammonium salts

The determination of copper(II), nickel(II) and cobalt(II) was carried out as diethyldithiocarbamate (DDTC) complexes in presence of aqueous solutions of cationic surfactants of hexadecyltrimethylammonium bromide, chloride and hydroxide (CTAB, CTAC, CTAOH). The presence of micellar systems avoids the previous step of solvent extraction necessary to the formation of the DDTC complexes in absence of micelles. The influence of the different micellar counterions on the analytical characteristics (sensitivity and detection limits) of the proposed method for spectrophotometric determination of Cu(II), Ni(II) and Co(II) was studied.

Determination of water-soluble vitamins in pharmaceutical preparations by reversed-phase high-performance liquid chromatography with a mobile phase containing sodium dodecylsulphate andn-propanol

SummaryA reversed-phase liquid chromatographic method with sodium dodecylsulphate-n-propanolwater as mobile phase has been used to separate and determine six water-soluble vitamins in twelve minutes. The analytical characteristics linear range, sensitivity, detection limits, and precision were evaluated. The lowest detection limits were those of nicotinic acid (not usually present in pharmaceutical products), 0.7 mgL−1, nicotinamide, 1.3 mg L−1, and pyridoxine, 1.4 mg L−1. When the method was applied to the determination of the vitamins in pharmaceutical samples the values found agreed with those on the labels.

Chromatographic Retention of Ni(II), Co(II) and Cu(II) as Diethyldithio-carbamate Complexes in Presence of Surfactant/n-Propanol/Water Systems: Determination of Micellar Binding Constants

Abstract This paper presents the values of the micellar binding constants of Ni(II), Co(II) and Cu(II) as complexes with sodium diethyldithiocarbamate, DDTC, in presence of hexadecyltrimethylammonium bromide, CTAB, and sodium dodecylsulphate, SDS, with larger amounts of n-Propanol as organic modifier, by High Performance Liquid Chromatography. Binding constants have been obtained from two equations: a) Arunyanarts treatment, very used for organic compounds but that is not take into account the influence of modifier and b) a multiple regression analysis that permits to consider the high quantities of n-Propanol.

Separation and Determination of Ni(II), Co(II) and Cu(II) by RP-HPLC with Hexadecyltrimethylammonium Bromide/n-Propanol Mobile Phases

SummaryThe effect of the presence of a cationic surfactant, hexadecyltrimethylammonium bromide (CTAB), and a short chain alcohol,n-propanol, in the mobile phase on the chromatographic retention of Co(II), Ni(II) and Cu(II) diethylammonium diethyldithiocarbamate complexes, has been studied. A simple isocratic reversephase method for the determination of the metals is proposed, using a mobile phase of composition CTAB 0.03 M/n-propanol 45 %v/v. Detection limits at pg levels were obtained for all solutes. The method was applied to the determination of the complexes in tap water samples at three different concentrations, with recoveries close to 100%. In order to evaluate the interaction between the metal complexes and the aggregates formed, the values of solute binding constants are calculated.

Ion exchange in concentrated media. Correlations for variation of selectivity coefficients with medium

Abstract An attempt to relate the different values of the ion-exchange selectivity coefficient in different media is made by considering the two phases as ionic solutions where the activity coefficients of species can be evaluated by means of Mikulins equation. The selectivity coefficients of the NH 4 + /H + , Na + /H + , and Li + /H + exchanges in a sulfonated cation exchanger and of the NO 3 − /Cl − exchange in a quaternary ammonium anion exchanger have been measured under different conditions characterized by the degree of crosslinking of the ion exchanger, the water activity of the solution, the concentration ratio of two counterions, and the concentration ratio of a third possible counterion. The water activity of the solution is an essential parameter to be controlled, particularly in dilute or moderately concentrated solutions. A representation of the experimental results on the ion-exchange selectivity coefficient is given in terms of two parameters allowing the selectivity coefficient to be predicted even in very concentrated ionic media.

Hexadecyltrimethylammonium bromide/ethanol/water systems as mobie phase in reverse phase high performance liquid chromatography. Study of metal-diethyldithiocarbamate complexes retention

SummaryThis paper presents the, chromatographic retention of Co(II), Ni(II) and Cu(II) as diethyldithiocarbamate complexes in the presence of hexadecyltrimethylammonium bromide/ethanol/water systems, as mobile phase, by reversed phase high performance liquid chromatography. The presence of an organic modifier reduces the retention times and improves the efficiency. In order to evaluate the interaction between the metal complexes and the mixed micellar system the values of solute binding constants are calculated in, two ways: a) Arunyanart and Cline-Loves treatment and b) multiple regression analysis taking account of the ethanol percentages.

Study of graphene dispersions in sodium dodecylsulfate by steady-state fluorescence of pyrene

HYPOTHESIS Aqueous solutions of ionic surfactants allow the exfoliation of graphene, that can be explained considering the adsorption model of ionic surfactants to hydrophobic surfaces. For many years, pyrene has been used as a fluorescent probe because its sensitivity to the micro-environment. The study of pyrene fluorescence in the presence of different graphene dispersions in an ionic surfactant, would improve the knowledge of the graphene-surfactant interactions. EXPERIMENTS Different dispersions of graphene in sodium dodecylsulfate were prepared at different weight ratios 0.5, 1 and 2%. The dispersions have been studied by Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. The influence of the dispersions on the pyrene fluorescence has been investigated. FINDINGS The graphene sheets modified by the surfactant quench the fluorescence of pyrene, which depends on the amount of graphene, the concentration of surfactant and the weight ratio. For surfactant concentrations below the critical micelle concentration, the quenching effect is higher as the weight ratio increases. Once this concentration is reached, the fluorescence increases slightly and then levels off. This behavior has been explained by the adsorption model. For a constant surfactant concentration, two straight lines can be observed in the Stern-Volmer plots whose cut-off point is approximately 20 mg L-1 of graphene.

Study of the binding constants of phenolic antioxidants with surfactant/n-propanol/water systems at high percentages of alcohol by RP-HPLC

In this work, the binding constants for five phenolic antioxidants with aggregates of cationic hexadecyltrimethylammonium bromide (CTAB) and anionic sodium dodecylsulfate (SDS) surfactants in n-Propanol at percentages higher than 20% v/v are calculated. The surfactant concentration needed to obtain aggregates in mobile phase was calculated in the presence of different n-Propanol percentages. The use of a multiple regression analysis allows one to obtain these constants at any percentage of the alcohol. The results are in very good agreement with the experimental data obtained in these media, taking into account the alcohol concentration in the used equations.