0000000000171054
AUTHOR
J. Sancenón
Fluorimetric determination of 1-naphthol and mixtures of carbaryl and 1-naphthol in micellar media
The interaction of 1-naphthol with different types of anionic, cationic and non-ionic surfactants has been studied spectrofluorimetrically in order to obtain a sensitivity enhancement in the determination of this compound. At neutral pH, cetyl trimethyl ammonium bromide (CTAB) provides a 2-fold sensitivity enhancement of 1-naphthol and exhibits a weak interaction with carbaryl. In strong alkaline medium carbaryl is hydrolyzed to 1-naphthol and in the presence of CTAB micells, a 5-fold sensitivity enhancement and a limit of detection of 0.2 μg·ml−1 with a 101±3% percentage of recovery is obtained. These facts permit the development of an accurate method for the fluorimetric analysis of 1-nap…
Flow-injection spectrophometric determination of propoxur with p-aminophenol
Abstract The spectrophotomeric determination of propoxur [2-(1-methyxlthoxy)phenyl methyl carbamate] was carried out with p -aminophenol (PAP) in a flow system. The method involves the on-line hydrolysis with NaOH of propoxur to 2-isopropoxyphenol and the oxidation of PAP to its relative quinone imine with KIO 4 and the reaction between the phenolate and the quinone imine. A four-channel flow manifold was employed to carry out all the different steps of the reaction considered, monitoring the indo dye formed at 600 nm. The developed procedure provides a typical calibration line of A = 0.000 7 + 1.8 × 10 3 C ( A = absorbance; C = concentration in M) with a regression coefficient of 0.9998 an…
Fluorimetric determination of binding constants between micelles and chemical systems
Abstract A fluorimetric method is adapted to determine the binding constants (K) between different systems and micelles. The method is based on the variation of the fluorescence of the system in the presence of increasing amounts of a surfactant agent. This method permits the determination of binding constants in strong acid or alkaline media. The binding constants of 1-naphthol and 2-(4-alkylamino-2 hydroxyphenyl)benzo-X azoles (X being an O or an S atom, PAS-O and PAS-S) with cationic, anionic, and nonionic surfactants have been determined by the proposed method. Values from 49,100 M−1 for the interaction between PAS-S and CTAB in basic medium to 10 M−1 for the interaction of 1-naphthol w…
Spectrophotometric determination of ethiofencarb in waters by reaction with p-aminophenol
An automatized procedure has been developed for the spectrophotometric determination of ethiofencarb in water by reaction with p-aminophenol after alkaline hydrolysis to obtain the corresponding phenol sulphone. The hydrolyzed samples are continuously introduced into different manifolds at the same time as 300 mg/l p-aminophenol, 0.004 mol/l KIO4 and 0.04 mol/l NaOH solutions. The absorbance is measured at 638 nm after a reaction time of 6 min in stop flow. This absorbance band corresponds to the indo dye obtained from the reaction between the phenol sulphone of ethiofencarb and the quinoneimine form of the p-aminophenol and it permits a matrix-free spectrophotometric determination of ethio…
Micellar enhanced fluorimetric determination of carbendazim in natural waters
Abstract A micellar enhanced flow-injection fluorimetric method was developed for the determination of carbendazim in natural water samples. The method is based on the direct injection of 500 μ1 of water into a three-channel flow manifold in which the samples are merged with a buffer solution and subsequently with a surfactant solution. Two alternative procedures were used: one based on the use of sodium dodecyl sulphate micelles in 0.1 M HCl, which permits a 2.6-fold enhancement of the sensitivity found in the absence of micelles to be obtained, and the other based on the use of cetyltrimethylammonium bromide in 0.1 M NaOH, which provides a 11.6-fold enhancement of sensitivity and a limit …
Surfactant Association: Recent Theoretical and Experimental Developments
A theoretical model describing the association of ionic surfactants into rod-shaped micelles is combined with an approximate formula for the viscosity increase induced by rod-shaped aggregates. It is shown that most of the thermodynamic parameters of the association model can be obtained from viscosity measurements. The approach is applied to micellar solutions of hexadecylpyridinium salts. The pronounced effect of counter-ion concentration on the growth of rod-shaped micelles can be attributed to a slightly higher degree of counter-ion association in the cylindrical part than in the end portions. An attempt is made to explain the finding that the degree of counter-ion association is virtua…