Preparation, characterization and application of polymethacrylate-based monolithic columns for fast and efficient separation of alkanes, alcohols, alkylbenzenes and isomeric mixtures by gas chromatography.

Application of monolithic columns in gas chromatography is still considered very limited. In this work, several polymethacrylate-based monolithic capillary columns were fabricated, characterized and used in gas chromatography. The five monomers used were: methyl methacrylate, (MMA), hexyl methacrylate (HMA), glycidyl methacrylate (GMA), 2-butoxyethyl methacrylate (BEMA) and isobornyl methacrylate (IBMA), while ethylene dimethacrylate was the crosslinker. The monoliths were synthesized in 30 cm length capillaries possessing inner diameters (i.d.) of 0.25 mm. The prepared monolithic columns were applied for separation of 3 series of homologous alkanes, alcohols and alkylbenzenes, as well as some isomeric mixtures. Van Deemter plots were used to optimize and compare the columns performance. The smaller methacrylates (MMA and GMA) exhibited higher porosity and permeability with low column backpressure values and poorer efficiency than the larger methacrylate monomers (HMA and BEMA). The columns prepared from IBMA monomer showed the highest pressure and the least separation efficiency. The fastest full separation of alkanes was achieved on HMA-co-EDMA column in about 3.0 min with resolution better than 2.73, while the fastest full separation of alcohols and alkylbenzenes was carried out using BEMA-co-EDMA column in less than 0.8 and 1.75 min with chromatographic resolution better than 1.27 and 1.85, respectively. Again, BEMA-co-EDMA column gave the best performance with the fastest and complete separation of all studied isomeric mixtures. For all tested series of solutes, the better separation efficiency was reached with tridecane, which gave 25,200 plates/m on the HMA-co-EDMA column. Another application was carried out using HMA-co-EDMA column for determination of myrcene and limonene, two monoterpenic isomers, in some fruit peels. Under the optimum GC conditions, a rapid separation of myrcene and limonene was achieved in less than 1.0 min with chromatographic resolution of 2.56. The highest contents of myrcene (0.131 mg/g) and limonene (1.225 mg/g) were measured in the hexane extracts of grapefruit and Egyptian orange, respectively. Finally, a comparison between the prepared columns and a commercial capillary column was performed. Based on the measured run time and HETP values, HMA-co-EDMA and BEMA-co-EDMA monolithic columns exhibited faster separation and higher efficiency for n-alkanes and alkylbenzenes than the TR-5 open tubular column, although they are 100 times shorter.

Curcumin protects against tartrazine-mediated oxidative stress and hepatotoxicity in male rats.

OBJECTIVE: Synthetic dyes have been reported to exert detrimental effects on the health of humans. This study evaluated the effects of a diet containing tartrazine (Tz) on rats which included: i) biochemical parameters including hepatic enzymes, kidney functions and profiles of lipids; ii) markers of oxidative stress in cells by measuring concentrations of malondialdehyde (MDA) and glutathione (GSH); iii) activities of selected, key hepatic antioxidant enzymes including catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx); iv) pathologies of liver. Also, protective effects of three doses of curcumin (CUR), a natural food coloring agent, on these parameters in rats that had been co-exposed to Tz. MATERIALS AND METHODS: Fifty Wistar male albino rats were randomly divided into five groups: Group I, control, where rats were fed a normal diet; Group II, rats were fed normal diets containing 7.5 mg Tz/kg diet, dry mass (dm); In Groups III, IV and V, rats were fed diets containing Tz plus 1.0, 2.0 or 4.0 g CUR/kg diet, dm, respectively. Whole blood was collected after 90 d of exposure, homogenates of liver were prepared and the above analyses were conducted. RESULTS: Exposure to Tz in the diet caused statistically significant (p<0.05) greater concentrations of lipids, hepatic enzymes, and kidney function parameters as well as the indicator of oxidative stress MDA. Alternatively, activities of several antioxidant enzymes (i.e. CAT, SOD and GPx) and concentration of the substrate GSH, an indicator of non-enzymatic antioxidant capability, were significantly (p<0.05) less than those in control rats not exposed to Tz. Tz caused various histopathological changes in livers of rats, which were characterized by hemorrhage and dilatation of the central vein and sinusoids, hepatocyte necrosis, intracellular vacuolization. Co-administration of 2.0 (Group IV) or 4.0 g CUR/kg diet (Group V) with Tz significantly mitigated effects on functions of liver and kidney and the profile of relative concentrations of lipids. CUR significantly (p<0.05), and almost completely, reversed effects on enzymatic and non-enzymatic antioxidant and indicators of oxidative stress about rats fed Tz (Group II) to values in control rats. However, co-administration of 1.0 g CUR with Tz (Group III) exhibited a negligible effect on those parameters. The results of this study suggest benefits of the use of CUR, as a promising natural food additive to counteract oxidative stress caused by dietary exposure to the synthetic dye Tz due to potent protective antioxidant activity. CONCLUSIONS: Blending some natural food additives, such as CUR with diets containing synthetic dyes, could moderate potential effects of these artificial dyes. Decreasing or removing toxins in food is an essential step for the amelioration of human health status and decreasing risk of onset or progression of degenerative diseases.

Synthesis, characterization and kinetics of formation of silver nanoparticles by reduction with adrenaline in the micellar media.

The present paper describes about the easy, simple and convenient procedure for the synthesis of silver nanoparticles (Ag-NPs) in aqueous solutions by the reduction of silver nitrate with adrenaline. The surfactant molecules of cetyltrimethylammonium bromide (CTABr) and sodium dodecyl ate (SDS) behaved differently during the reduction of Ag(+) ions by adrenaline. The obtained data suggest that the variation of [CTABr] gave a maxima-like curve for rate constant versus [CTABr], while, the values of rate constant decreased with the increase in [SDS]. The addition of surfactant molecules stabilized the Ag-NPs. The UV-Visible spectra were analyzed to deduce the particle size. The calculated sizes of the nanoparticles were further compared by the TEM images. The XRD spectrum confirmed the crystalline nature of silver nanoparticles having the face-centered cubic crystal structure. The edge length of unit cell was found 4.076 Å. The kinetics of formation of Ag-NPs was performed at different concentrations of adrenaline, AgNO3, NaOH and [surfactant]. The values of rate constant were independent on [adrenaline] and [AgNO3]. The increase in [NaOH] increased the rate of agglomeration of silver particles to form Ag-NPs. A linear relationship was obtained for the plot of rate constant versus [NaOH].