Biomedical subjects

J Domínguez-Alvarez

Publications and source records attributed to J Domínguez-Alvarez.

3 recordsLinked to original sources

PubMed2003

Prediction of the behaviour of organic pollutants using cloud point extraction.

A preconcentration study based on the cloud point phenomenon was carried out for a set of triazine herbicides, three of them chloro-substituted and three of them methylthio-substituted. Concentration factors and recoveries were calculated as function of the percentage of the non-ionic surfactant Triton X-114 employed. From these values, obtained from a cloud point extraction (CPE) procedure, the distribution coefficient between the Triton X-114 micelles and water, Kc, prior to CPE was calculated for each triazine and related to the corresponding octanol-water partition coefficient, Kow. In order to confirm the results obtained with the triazine herbicides, two sets of data from chemically different organic pollutants--organophosporous and chlorophenols--obtained from the literature were assessed, concluding that they display a similar behaviour to that of the triazine herbicides. This can be used to predict the CPE behaviour of other organic pollutants from their octanol-water partition coefficients. The Kc values were compared with the analyte concentration ratio in the surfactant-rich phase and aqueous phase (Ksa) with a view to obtaining a link between the analyte behaviour prior to and after cloud point extraction procedures.

Environmental Pollutants↗

PubMed2003

Solid-phase extraction and sample stacking-micellar electrokinetic capillary chromatography for the determination of multiresidues of herbicides and metabolites.

Micellar electrokinetic capillary chromatography (MEKC) with diode array detection was used for the separation of 13 compounds (eight herbicides widely used in agriculture: metribuzin, lenacil, ethofumesate, atrazine, terbutryn, isoproturon, chlorotoluron and linuron, and five of their principal degradation products; namely, deethylatrazine, 2-hydroxyatrazine, deethyl-2-hydroxyatrazine, deisopropylatrazine and 3-chloro-4-methylphenylurea). Peak separation for the 13 analytes was not successful when a single surfactant system was employed, neither sodium dodecyl sulfate (SDS) nor dioctyl sulfosuccinate (DOSS) sodium salt. However, a mixture of these herbicides was successfully separated using a mixed micellar system involving SDS-DOSS in less than 14 min. An application study of an on-line concentration technique for MEKC was carried out to enhance sensitivity. The optimized on-line stacking procedure consisted simply of the addition of 50 mM of sodium chloride to the injection sample, the stacking effect being more intensive as analyte polarity increased. When this stacking procedure was combined with an off-line sample preconcentration step, based on solid-phase extraction, analytes could be detected in the ppb range. The whole method was applied to ultra-high-quality and natural waters. Linear relationships between the analytical signal and the initial analyte concentration were found to be independent of the type of water, except for the more polar analytes for which small differences were observed.

Chromatography, Micellar Electrokinetic Capillary↗

PubMed2000

Determination of triazine herbicides in natural waters by solid-phase extraction and non-aqueous capillary zone electrophoresis.

Capillary zone electrophoresis (CZE) in an organic medium was used to analyse triazines at sub-ppb concentration levels in natural waters after a preconcentration step using conventional C18 cartridges and new Oasis HLB devices. With both sorbents, satisfactory results were obtained on analysing deionized water. However, on analysing natural waters, both sorbents showed very different types of behaviour. The different variables affecting the elution of both sorbents were studied, resulting in the choice of Oasis HLB as the most suitable for later separation by CZE in non-aqueous medium. Combination of a preconcentration step with electrokinetic injection revealed that capillary electrophoresis with simple UV detection can also be used satisfactorily for the quantification of micropollutants in natural waters. The detection limits obtained varied between 0.01 and 0.05 microg l(-1), depending on the type of matrix analysed. The day-to-day precision varied between 0.9% and 2.3%, expressed as the relative standard deviation.

Electrophoresis, Capillary↗