Tuning of preparation conditions, such as variations in the amount of a porogen, concentration of an aqueous acid catalyst, and adjustment in polymerization temperature and time, towards optimized chromatographic performance of thermally polymerized monolithic capillaries prepared from 3-(methacryloyloxy)propyltrimethoxysilane has been carried out. Performance of capillary columns in reversed-phase liquid chromatography was assessed utilizing various sets of solutes. Results describing hydrophobicity, steric selectivity, and extent of hydrogen bonding enabled comparison of performance of hybrid monolithic columns prepared under thermal (TSG) and photopolymerized (PSG) conditions. Reduced amounts of porogen in the polymerization mixture, and prolonged reaction times were necessary for the preparation of monolithic columns with enhanced retention and column efficiency that reached to 111,000 plates/m for alkylbenzenes with shorter alkyl chains. Both increased concentration of catalyst and higher temperature resulted in faster polymerization but inevitably in insufficient time for pore formation. Thermally polymerized monoliths produced surfaces, which were slightly more hydrophobic (a methylene selectivity of 1.28±0.002 TSG vs 1.20±0.002 PSG), with reduced number of residual silanols (a caffeine/phenol selectivity of 0.13±0.001 TSG vs 0.17±0.003 PSG). However, steric selectivity of 1.70±0.01 was the same for both types of columns. The batch-to-batch repeatability was better using thermal initiation compared to monolithic columns prepared under photopolymerized conditions. RSD for retention factor of benzene was 3.7% for TSG capillaries (n=42) vs. 6.6% for PSG capillaries (n=18). A similar trend was observed for columns prepared within the same batch.
Zinc and copper status was evaluated in nineteen children with chronic diarrhea. An intestinal biopsy suggested that eight of these patients had celiac disease and eleven suffered chronic diarrhea without malabsorption and had normal villi or minimal changes. They were studied for malabsorption and compared with two control groups consisting of nineteen healthy and eleven malnourished children. Plasma zinc was depressed in the celiac disease group when compared with the normal children, but was similar to that of the malnourished children. Hair zinc was also depressed for the chronic diarrhea groups (23.2 +/- 15.2 and 34.4 +/- 21.9 micrograms/g for those with or without malabsorption respectively, vs. 97.9 +/- 15.2 for the healthy group). Plasma and hair copper values were diminished in both groups with chronic diarrhea. A significant correlation was found between plasma carotene levels after oral carotene overload, and both plasma zinc and hair copper values (r = 0.62, p less than 0.01 and r = 0.56, p less than 0.05, respectively). There was also a significant correlation between plasma zinc and plasma protein (r = 0.54, p less than 0.05). Hair determinations seem to be more sensitive than plasma values to changes in zinc or copper status in chronic diarrhea. Chronic diarrhea in children is associated with lower levels of zinc and copper, especially when accompanied by malabsorption.
This work aims at obtaining experimental data on ozonation of 1,2-dihydroxybenzene (DHB) in the presence of activated carbon, with a view to assessing possible changes in its surface chemical structure and adsorption capacity. Experiments were conducted in a 0.5 L reactor, loaded with 2 g Filtrasorb 400 granular activated carbon, and 1-5 mM DHB aqueous solution at pH 2-8. Ozone gas was generated with an Ozocav generator, and fed into the reactor for a given exposure time, in the range 0.5-240 min, at 25 degrees C and 1 atm. After each run, liquid and activated carbon samples were taken for chemical assays. Soluble organic groups present on the active carbon surface were desorbed and analysed by GC-MS and HPLC. Activated carbon chemical surface properties were analysed using TPD, FT-IR, and XPS techniques. Reactions between ozone and adsorbed DHB were shown to be fast, leading to formation of C-6, C-4 and C-2 by-products. Oxygenated surface groups, particularly, COOH and C = O, increased as a result of ozonation.
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