Selective silica-based sorbent materials synthesized by molecular imprinting for adsorption of pharmaceuticals in aqueous matrices.

The presence of pharmaceuticals in aqueous environmental matrices often requires efficient and selective preconcentration procedures. Thus, silicas (SILs) were synthesized by a molecular imprinting technique using an acid-catalyzed sol-gel process and the following drugs as templates: fluoxetine, gentamicin, lidocaine, morphine, nifedipine, paracetamol, and tetracycline. The materials were subjected to sorbent extraction assisted by ultrasonic treatment to remove the drugs and the consequent formation of molecular imprinted cavities. The surface area of the resulting materials ranged from 290 to 960 m(2)/g. Adsorption tests were performed with the molecular imprinting phases. In terms of the potential selectivity, the SILs were subjected to the adsorption of drugs from samples such as potable and surface water. The adsorption capacity remained in the range between 55 and 65% for both matrices, while for the nonimprinted SIL it remained between 15 and 20%.

The interaction of encapsulated pharmaceutical drugs with a silica matrix.

A series of seven drugs, namely, fluoxetine, gentamicin, lidocaine, morphine, nifedipine, paracetamol and tetracycline, were encapsulated. The encapsulated systems were characterized using a series of complementary techniques: Fourier-transform infrared spectroscopy (FT-IR), diffusive reflectance spectroscopy in the UV-vis region (DRS) and X-ray photoelectron spectroscopy (XPS). According to the DRS spectra, most of the encapsulated systems showed a band shift of the maximum absorption when compared with the corresponding bare pharmaceutical. Additionally, after encapsulation, the drugs exhibited infrared band shifts toward higher wavenumbers, which in turn provided insight into potential sites for interaction with the silica framework. The amine group showed a band shift in the spectra of almost all the drugs (except nifedipine and tetracycline). This finding indicates the possibility of a hydrogen bonding interaction between the drug and the silica via electron donation from the amine group to the silica framework. XPS confirmed this interaction between the pharmaceuticals and the silica through the amine group. A correlation was observed between the textural characteristics of the solids and the spectroscopic data, suggesting that the amine groups from the pharmaceuticals were more perturbed upon encapsulation.

Combining silica-based adsorbents and SPME fibers in the extraction of the volatiles of beer: an exploratory study.

A series of silica-based materials were employed as sorbents within solid-phase microextraction vials. The aim of the study was to evaluate the effect of an additional phase on the distribution of the volatile and less volatile analytes. The adsorption of six probe molecules, namely isoamyl acetate, ethyl hexanoate (ethyl caproate), phenylethyl alcohol, ethyl octanoate (ethyl caprilate), 2-phenylethyl acetate, and ethyl decanoate, was monitored by detecting the desorbed amount on a DVD-CAR-PDMS fiber from Pilsen beer. The microextraction process involved the presence of different silica-based phases produced via different methods: xerogel produced by hydrolytic and non-hydrolytic routes, aerogel, pyrogenic, and precipitated silica. The resulting data are discussed in correlation with sorbent texture properties (specific area and pore diameter). The modification of silica with alkyl groups also affects the preconcentrated amount of the target molecules in the headspace. The presence of sorbents was shown to affect the analyte signal more than the addition of NaCl or the use of ultrasound.

Octadecylsilane-modified silicas in the adsorption of toluene.

A series of octadecylsilane-modified silicas were prepared by sol-gel and grafting methods. Carbon contents and octadecyl chain conformations were shown to depend on the preparative route. Grafting engenders a low carbon content and a liquid-like chain conformation, while the sol-gel method affords a much higher carbon content and a crystalline conformation. The relationships between the toluene adsorption of the hybrid silicas and their chain conformations, their carbon contents and their textural characteristics are discussed. These sorbents, when used in combination with ultraviolet diffuse reflectance spectroscopy (UV DRS), can be employed as a rapid screening method for detection of aromatic compounds in water and air environmental matrices.

Octadecylsilane hybrid silicas prepared by the sol-gel method: morphological and textural aspects.

A series of octadecylsilane-modified silicas was prepared by the sol-gel method through the hydrolysis and cocondensation of tetraethylorthosilicate (TEOS) with octadecyltriethoxysilane (ODS). The ODS:TEOS ratio was varied between 0:100 and 100:0. The resulting carbon content was between 2.5 and 53.4%. In the case of pure ODS, the resulting silica presented 68.6% of C. Hybrid silicas were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, and (29)Si nuclear magnetic resonance spectroscopy. Spheres of ca. 0.5-1.0 microm were obtained in the case of hydrolysis of pure TEOS. The combination of ODS:TEOS ratio yielded systems combining spherical and lamellar patterns zones. Monitoring the particle growth, it seems that spherical particles grow around lamellar zones, these latter concentrating the organosilicon moieties. The degree of cross-linking of ODS moieties was shown to be dependent on the ODS addition time and stirring speed.