172 research outputs found
Weak anion-exchange hypercrosslinked sorbent in on-line solid-phase extraction-liquid chromatography coupling to achieve automated determination with an effective clean-up
A mixed-mode polymeric sorbent was on-line coupled to liquid chromatography (LC) for the first time and applied it to the selective solid-phase extract a group of pharmaceuticals in complex environmental water samples. The mixed-mode polymeric sorbent is a high-specific surface area hypercrosslinked polymer resin (HXLPP) in the form of monodisperse microspheres further modified with 1,2-ethylenediamine (EDA) moieties. These properties allows its application as a weak anion-exchange (WAX) sorbent in the on-line solid-phase extraction (SPE) coupling. The on-line SPE-LC method developed using the HXLPP-WAX sorbent was successfully applied to percolate a large volume of ultrapure (500 ml), river (250 ml) and effluent sewage (100 ml) water samples. In all the cases, the HXLPP-WAX resin provided near total recoveries of the most acidic compounds studied and clean chromatograms. This is because the ion-exchange interactions enable a washing step to be added to the SPE protocol that removes the compounds with weak acidic, neutral and basic properties from the sample matrix
Hydrophilic hypercrosslinked polymeric sorbents for the solid-phase extraction of polar contaminants from water
Three new hypercrosslinked polymers with hydrophilic character arising from hydroxyl moieties in their skeletons have been prepared in microsphere format and applied to the off-line solid-phase extraction (SPE) of polar compounds from water samples. For sample volumes of 1000 ml, the recoveries of various polar pesticides, such as oxamyl, methomyl, selected phenolic compounds, as well as some pharmaceuticals, were close to 90%. The HXLPP-polar polymer with the best performance characteristics was applied to real samples. Its performance was also compared to commercially available sorbents, such as LiChrolut EN (hydrophobic, hypercrosslinked), Oasis HLB (hydrophilic, macroporous) and Isolute ENV+ (hydrophilic, hypercrosslinked); the new sorbent out-performed the commercially available sorbents. The polymer was applied successfully in off-line SPE of river water samples followed by liquid chromatography and ultraviolet detection, providing a good linear range and detection limits of 0.2 μg l-1 for the majority of the compounds, with the exception of oxamyl, methomyl, guaiacol and salicylic acid where the detection limit was 0.5 μg l-1
Synthesis and application of hypercrosslinked polymers with weak cation-exchange character for the selective extraction of basic pharmaceuticals from complex environmental water samples
The synthesis of high specific surface area sorbents (HXLPP-WCX) in the form of hypercrosslinked polymer microspheres with narrow particle size distributions, average particle diameters around 6 µm, and weak cation exchange (WCX) character, is described. The WCX character arises from carboxylic acid moieties in the polymers, derived from the comonomer methacrylic acid. A novel HXLPP-WCX sorbent with an attractive set of chemical and physical properties was then used in an off-line solid-phase extraction (SPE) protocol for the selective extraction of a group of basic compounds from complex environmental samples, a priority being the clean separation of the basic compounds of interest from acidic compounds and interferences. The separation power of the new sorbent for basic pharmaceuticals was compared to two commercially available, mixed-mode sorbents, namely Oasis WCX and Strata X-CW. Under identical experimental conditions, HXLPP-WCX was found to deliver both higher capacity and better selectivity in SPE than either of the two commercially available materials. In an optimised SPE protocol, the HXLPP-WCX sorbent gave rise to quantitative and selective extractions of low µg l-1 levels of basic pharmaceuticals present in 500 ml of river water and 250 ml of effluent waste water
Effect of the anodization voltage on the porewidening rate of nanoporous anodic alumina
A detailed study of the pore-widening rate of nanoporous anodic alumina
layers as a function of the anodization voltage was carried out. The study
focuses on samples produced under the same electrolyte and concentration but
different anodization voltages within the self-ordering regime. By means of
ellipsometry-based optical characterization, it is shown that in the
porewidening process, the porosity increases at a faster rate for lower
anodization voltages. This opens the possibility of obtaining three-dimensional
nanostructured nanoporous anodic alumina with controlled thickness and
refractive index of each layer, and with a refractive index difference of up to
0.24 between layers, for samples produced with oxalic acid electrolytes
Hypercrosslinked materials : preparation, characterisation and applications
This review article provides an overview of hypercrosslinking technology. In particular, it covers the preparation and characterisation of hypercrosslinked materials and their applications. The synthesis section examines the different monomers, precursor polymers and reagents used to prepare hypercrosslinked materials, but also the different synthetic approaches disclosed in the literature. The various chemical modification reactions relevant to this area are also reviewed. Several examples of applications for hypercrosslinked materials are described; these applications are grouped into thematic areas such as chromatography, gas storage and the trapping of organic contaminants
Hypercrosslinked materials
This chapter describes the chemistry of hypercrosslinked materials, and presents a description of their synthesis, defining physico-chemical features and their most important applications. The synthesis section will examine the different monomers, precursor polymers, reagents and synthetic strategies used to prepare hypercrosslinked materials. Each synthesis section also details the chemical and morphological properties of the hypercrosslinked materials and the main field of application
Fabrication of self-ordered nanoporous alumina for optical and structural characterization
Presentem la fabricació, caracterització estructural i òptica de
membranes d'alúmina nanoporosa autoordenada. Les mostres
han estat fabricades per el procés de doble anodització.
La morfologia de les membranes obtinguda mitjançant les diferents
condicions d'anodització ha estat examinada amb un microscopi
electrònic d'escombrat per tal d'estimar les seves
propietats geomètriques. Les propietats estructurals estudiades
mitjançant difracció de raigs X mostren que durant el procés
de recuit termic, des de 600 ºC fins a 1200 ºC, l'alúmina
nanoporosa ha cristal·litzat des de la fase amorfa fins a les formes
gamma i alfa (cristal·lines). L'espectre de la transmissió
òptica de les membranes d'alúmina porosa autoordenada va
ser mesurat mitjançant un espectròmetre UV-VIS en el rang
300 - 1000 nmWe present the fabrication and optical and structural characterization
of self-ordered nanoporous alumina membranes.
The samples were fabricated using a two-step anodization
process. The morphology of the membranes produced using
different anodizing conditions was examined with a scanning
electron microscope in order to estimate their geometrical
properties. The structural properties studied by X-ray diffraction
showed that nanoporous alumina is crystallized from
amorphous phase to gamma and alpha (crystalline) forms during
annealing at 600 ºC to 1200 ºC. The optical transmission
spectra of the membranes were measured using a UV-VIS
spectrometer in the range of 300 - 1000 nm
Photonic stop bands in quasi-random nanoporous anodic alumina structures
The existence of photonic stop bands in the self-assembled arrangement of
pores in porous anodic alumina structures is investigated by means of rigorous
2D finite- difference time-domain calculations. Self-assembled porous anodic
alumina shows a random distribution of domains, each of them with a very
definite triangular pattern, constituting a quasi-random structure. The
observed stop bands are similar to those of photonic quasicrystals or random
structures. As the pores of nanoporous anodic alumina can be infiltrated with
noble metals, nonlinear or active media, it makes this material very attractive
and cost-effective for applications including inhibition of spontaneous
emission, random lasing, LEDs and biosensors
1-D nanoporous anodic alumina rugate filters by means of small current variations for real-time sensing applications
pH-responsive drug delivery system based on hollow silicon dioxide micropillars coated with polyelectrolyte multilayers
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