Examinando por Autor "Silva, Mariana"

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Environmental chiral analysis of β-blockers: Evaluation of different n-alkyl-modified SBA-15 mesoporous silicas as sorbents in solid phase extraction
(CSIRO PUBLISHING, 2018) Silva, Mariana; Morante-Zarcero, Sonia; Pérez-Quintanilla, Damián; Marina, M.L.; Sierra, Isabel
The extraction and preconcentration of chiral β-blockers in environmental water was evaluated by solid-phase extraction (SPE) employing an SBA-15 ordered mesoporous silica functionalised with alkyl chains of different length. The materials were characterised by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption–desorption isotherm measurements and elemental analysis. Important parameters influencing extraction efficiency, including the type and amount of sorbent and the breakthrough volume, were optimised. The results obtained showed that the organic chain length played an important role in the behaviour of these sorbents. Under optimised conditions, using 200 mg SBA-15-C8 as sorbent, a simple analytical method based on off-line SPE coupled to chiral capillary electrophoresis with diode array detection (SPE-chiral CE-DAD) was developed. Method detection and quantification limits were lower than 0.6 and 1.9 µg L −1 respectively for all enantiomers, with a preconcentration factor of 500-fold. The method was successfully applied to the chiral analysis of atenolol, metoprolol, pindolol and propranolol in river and sewage water samples. Satisfactory recoveries (between 86 ± 2 and 98 ± 1 %) and repeatability (relative standard deviation (RSD) < 9 %, n = 3) were obtained. Metoprolol was detected in sewage water at a concentration of 10.7 and 9.9 µg L−1 and an enantiomeric fraction of 0.52 and 0.48 for the first- and the second-migrating enantiomers respectively. These results emphasise the importance of enantioselective analysis for environmental risk assessment.
Ordered mesoporous silica functionalized with ß-cyclodextrin derivative for optical isomer separation of flavanones and flavanone glycosides by nano-liquid chromatography and capillary electrochromatography
(Elsevier, 2017) Silva, Mariana; Pérez-Quintanilla, Damián; Morante-Zarcero, Sonia; Sierra, Isabel; Marina, María Luisa; Aturki, Zeineb; Fanali, Salvatore
In this paper a novel chiral stationary phase (CSP) was prepared by the immobilization of a ß-CD derivative (3,5-dimethylphenylcarbamoylated ß-CD) onto the surface of amino-functionalized spherical ordered mesoporous silica (denoted as SM) via a urea linkage using the Staudinger reaction. The CSP was packed into fused silica capillaries 100 ¿m I.D. and evaluated by means of nano-liquid chromatography (nano-LC) and capillary electrochromatography (CEC) using model compounds for the enantioseparation and the diastomeric separation. The compounds flavanone, 2¿-hydroxyflavanone, 4¿-hydroxyflavanone, 6-hydroxyflavanone, 4¿-methoxyflavanone, 7-methoxyflavanone, hesperetin, hesperidin, naringenin, and naringin were studied using reversed and polar organic elution modes. Baseline optical isomers resolution and good results in terms of peak efficiency and short analysis time of all studied flavonoids and flavanones glycosides was achieved in reversed phase mode, using a mixture of MeOH/H2O, 10 mM ammonium acetate pH 4.5 at different ratios as mobile phase. For the polar organic mode using 100 % of MeOH as mobile phase, the CSP showed better performances, the baseline chiral separation of several studied compounds occurred in an analysis time of less than 10 min. Also good results were achieved by CEC employing two different mobile phases. The use of MeOH/H2O, 5 mM ammonium acetate buffer pH 6 (90/10, v/v) was very effective for the chiral resolution of flavanone and its methoxy and hydroxy derivatives.
Simultaneous determination of pindolol, acebutolol and metoprolol in waters by differential-pulse voltammetry using an efficient sensor based on carbon paste electrode modified with amino-functionalized mesostructured silica
(Elsevier, 2019) Silva, Mariana; Morante-Zarcero, Sonia; Pérez-Quintanilla, Damián; Sierra, Isabel
In this work, hexagonal mesoporous silica (HMS) and amino-functionalized HMS (HMS-NH2) were prepared and incorporated into carbon paste electrodes (CPEs) to obtain electrochemical sensors for pindolol (Pin), acebutolol (Ace) and metoprolol (Met) determination in waters by voltammetric techniques. The materials were characterized and they showed high specific surface area, large pore volume and a quasi-spherical morphology. Firstly, the electrochemical behaviour of the modified CPEs was studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Then, the dependence of the current intensity with the electrolyte support (type and pH) and the accumulation time was investigated to optimize the experimental conditions for simultaneous β-blockers determination by DPV. Results showed that the sensor modified with functionalized silica (NH2-HMS-CPE) exhibited strong adsorption activity, showing three well-defined peaks in the differential pulse voltammograms, that appeared at about +0.85 V (Pin), +1.11 V (Ace) and +1.45 V (Met). This fact can be attributed to the high surface area of the material, with a 3 D wormhole-like channel structure that favoured excellent pore accessibility, and the synergistic effect produced by the grafted amino groups producing hydrogen bond interactions with the oxygen atoms of the target β-blockers. The prepared sensor exhibits good reproducibility, wide linear ranges and very low detection limits (0.1, 0.046 and 0.23 μmol L−1 for Pin, Ace and Met, respectively). Moreover, the NH2-HMS-CPE was successfully applied for the simultaneous determination of Pin, Ace and Met in tap, mineral, river and sewage effluent waters with simple sample treatment (recoveries 97–112%).