0000000000139586
AUTHOR
J.s.esteve Romero
showing 6 related works from this author
Acid—base properties of azo dyes in the presence of surfactants
1991
Abstract The changes in the acid—base properties of an azo dye produced by the presence of surfactants, at surfactant concentrations below and above the CMC, are quantitatively described using a simple model and spectrophotometric and potentiometric measurements. The azo dye formed by aniline and N -(1-naphthyl)-ethylenediamine, and the surfactants sodium dodecyl sulphate, Triton X-100 and N -cetylpyridinium chloride (NCPC) are used. The protonation constants of the free and surfactant-bound dye species, the binding constant of the protonated and unprotonated forms of the dye, and the average aggregation number of the dye—NCPC aggregates are evaluated.
Flow-injection spectrophotometric determination of arylamines and sulphonamides by diazotization and coupling in a micellar medium
1991
Abstract In a sodium dodecyl sulphate (SDS) micellar solution, the rate of coupling of a diazonium ion with N-(1- naphthyl)ethylenediamine (NED) increases greatly, the protonation of the resulting azo dyes takes place at higher pH values and the dyes are more soluble. These favourable features were applied to the development of a simple flow-injection spectrophotometric procedure for the determination of diazotizable substances of pharmaceutical interest. Limits of detection in the range 0.2–0.5 μg ml−1 (signal-to-noise ratio=3), with relative standard deviation of 0.7–3% (n=3) for 5 μg ml−1 standards, were obtained.
Inhibition of the precipitation of barium salts in sodium dodecyl sulfate/0.1 M HCl/n-pentanol microemulsions and liquid crystals
1989
Abstract The phase ternary diagram of the sodium dodecyl sulfate (SDS)/0.1 M HCl/n-pentanol system is studied. Three monophase regions were observed: water rich and n-pentanol rich microemulsions, and a liquid crystal. These media have a strong ability to control the rate of crystal growth of barium sulfate and barium dodecyl sulfate, the precipitation being totally inhibited in the liquid crystal region.
Colorimetric determination of arylamines and sulphonamides by diazotization and coupling in a micellar solution
1989
Abstract The use of a micellar solution as a means for improving the colorimetric determination of arylamines by diazotization and coupling is studied. Sodium dodecylsulphate (SDS), Triton X-100 (TX-100) and N -cetylpyridinium chloride (NCPC), together with the diazotizable substances aniline and sulphanilic acid and the coupling agents 1-naphthylamine and N -(1-naphthyl)ethylenediamine are used as model compounds. The protonation constants of the dyes follow the order SDS>H 2 O>TX-100>NCPC. In an SDS micellar solution the coupling rate increases greatly, allowing the rapid formation of the protonated dyes in an acetate buffer. Other advantages are the possibility of analysing very non-pola…
Determination of aniline in vegetable oils by diazotization and coupling in a microemulsion medium
1990
Abstract A microemulsion containing sodium dodecyl sulphate and n -pentanol in a mass ratio of 1 : 4, water and a vegetable oil was investigated using pseudo-tenary phase diagrams. The medium can co-solve important amounts of vegetable oils and aqueous solutions over a wide range of ionic strengths. A procedure for the determination of 1.4–140 μg ml −1 of aniline in vegetable oils using ionic diazotization and coupling reactions was developed. The absorbance was measured in an optically clear microemulsion containing 4% or 20% of oil. The procedure is much simpler and rapid than the official chromatographic methods and gives almost the same limits of detection (ca. 05 μg ml −1 ) using no mo…
Formation rates and protonation constants of azo dyes in a sodium dodecylsulphate micellar solution.
1991
The effects of a sodium dodecylsulphate micellar solution on the coupling rates of several diazotizated arylamines with N-(1-naphthyl)-ethylenediamine and the shifts in the protonation constants of the corresponding azo dyes are quantitatively studied. Aniline, o-, m- and p-aminobenzoic acids, ethyl p-aminobenzoate and several sulphadrugs are used, and the relationships among the intensity of the effects and the molecular structure of the diazonium ions and the dyes are discussed. A single simplified procedure for the determination of all the substances at pH = 1.3 +/- 0.3, where coupling is quickly completed to directly produce the protonated form of the dyes, is established and applied to…