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At least 1,045 records · Page 58Linked to original sources
PubMed1990

Use of polymeric sorbents for the off-line preconcentration of priority pollutant phenols from water for high-performance liquid chromatographic analysis.

The use of porous polymeric minicolumns for the determination of phenols from the U.S. Environmental Priority Pollutant List was studied. For the off-line preconcentration of priority pollutant phenols from water by solid-phase extraction, minicolumns packed with 1,4-di(methacryloyloxymethyl)naphthalene-divinylbenzene copolymer and Amberlite XAD-4 were used. In order to compare the sorption properties of these polymeric sorbents, the recoveries and breakthrough volumes of phenol, p-nitrophenol, 2,4-dinitrophenol, o-chlorophenol, o-nitrophenol, 2,4-dimethylphenol, 4-chloro-m-cresol, 4,6-dinitro-o-cresol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol were studied.

Acrylates↗
PubMed1987

Determination of vinyl chloride monomer residue in poly(vinyl chloride) at the parts-per-billion level with an automatic purge-and-trap technique.

A method for the determination of vinyl chloride residue in poly(vinyl chloride) using a commercial purge-and-trap ancillary unit has been developed. Concentrations lower than 10 ppb (10(9] with relative standard deviations in the region of 10% in up to 24 samples are detectable with fully automatic operation without operator attendance. With multiple extraction of the same sample an external standard is used; the matrix does not have any influence on the recovery of vinyl chloride.

Chromatography, Gas↗
PubMed1975

Analytical separation of amino acids on a cation-exchange resin cross-linked with m-divinylbenzene.

The elution bands of acidic and neutral amino acids of protein hydrolysates, emerging from the column of a cation-exchange resin cross-linked with pure m-divinylbenzene, are narrower than those from a resin prepared from styrene and technical divinylbenzene. As a result of these narrower bands, a more complete resolution of the critical pairs threonine-serine, glycine-alanine and tyrosine-phenylalanine is obtained. The most probable reason for the narrower elution peaks is the more rapid diffusion of the exchanged components through the bulk of the resin as a result of a more regular arrangement of cross-linkages in the cation-exchange resin prepared from m-divinylbenzene.

Amino Acids↗
PubMed1997

Use of reversed-phase high-performance liquid chromatography on polystyrene-divinylbenzene columns for the rapid separation and purification of acid-soluble nuclear proteins.

The suitability of polystyrene-divinylbenzene reversed-phase HPLC columns for rapid separation and purification of acid-soluble nuclear proteins was evaluated. We used a polystyrene-divinylbenzene reversed-phase HPLC column (PLRP-S) for purification of nuclear proteins extracted with 0.3 M HCl or 5% HClO4. We are able to obtain electrophoretically pure fractions for a number of nuclear proteins including HMG14, HMG17 and variants of histone H3. The identity of proteins in these fractions was confirmed by immunochemical analysis, protein sequencing, mass spectrometry and migration on two-dimensional polyacrylamide gel electrophoresis. These methods do not require special preparation of the sample and are quicker than similar published methods.

Chromatography, High Pressure Liquid↗
PubMed1997

Modification of polystyrenic matrices for the purification of proteins. II. Effect of the degree of glutaraldehyde-poly(vinyl alcohol) crosslinking on various dye ligand chromatography systems.

A poly(styrene-divinylbenzene) chromatography matrix, CG1000sd (TosoHaas) has been modified by the adsorption and crosslinking of poly(vinyl alcohol) (PVA) to create a matrix suitable for the attachment of dye ligands for the adsorption of lysozyme. However, it is shown that there was limited recovery and repeated drops in capacity with adsorption of human serum albumin (HSA). The effect of changing the nature of the PVA crosslinking on the HSA binding characteristics was studied, as well as the effect of using differing dye ligands. The total amount of irreversible HSA binding decreased with greater crosslinking and there were large differences in HSA adsorption characteristics between differing dye types.

Adsorption↗
PubMed1997

Modification of polystyrenic matrices for the purification of proteins. III. Effects of poly(vinyl alcohol) modification on the characteristics of protein adsorption on conventional and perfusion polystyrenic matrices.

Poly(styrene-divinylbenzene) (PS-DVB) chromatography matrices, CG1000sd 20-50 microns (TosoHaas), PLRP4000s 15-25 microns, PLRP4000s 50-70 microns (Polymer Laboratories) have been modified by the adsorption and crosslinking of poly(vinyl alcohol) (PVA) to create a matrix suitable for the attachment of dye ligands. The adsorption capacities of lysozyme and HSA on these Procion Yellow HE-3G dyed PVA modified PS-DVB matrices were measured at various flow-rates and the capacities were compared with a Procion Yellow HE-3G dyed OH-activated POROS 20, 20-micron matrix (PerSeptive Biosystems). The adsorption of small proteins was not hindered by the smaller pores of the CG1000sd beads, but as protein size increased, and at high flow-rates, a high mass transfer rate became more dependent on large pore size and small particle diameter.

Adsorption↗
PubMed1998

Comparison of different sorbents for on-line liquid-solid extraction followed by high-performance liquid chromatographic determination of nitrogen-containing pesticides.

LiChrolut EN [poly(styrene-divinylbenzene), PSDVB], Carbograph (graphitized carbon black, GCB), Isolute CN (cyanopropylsilica), Isolute C2 (ethylsilica), and LiChrospher RP18 (octadecylsilica) were studied for on-line solid-phase extraction of twelve nitrogen containing pesticides from water. Determination (UV 210 nm) was performed with a Spherisorb C8 analytical column and an acetonitrile-water gradient. The mean recoveries from 50 ml ranged from 83% for RP18 to 44% for GCB, and decreased in the following order: RP18, CN, LiChrolut EN, C2, and GCB. GCB showed poor recoveries due to incomplete desorption with the acetonitrile-water gradient used, and memory effects were detected. Backflush was needed to elute selected pesticides from GCB and from LiChrolut EN. Breakthrough volumes were 50-100 ml for most selected pesticides with silica-based phases, whereas LiChrolut EN allowed larger sample volumes without observable losses.

Carbon↗
PubMed2003

pH effect of coagulation bath on the characteristics of poly(acrylic acid)-grafted and poly(4-vinylpyridine)-grafted poly(vinylidene fluoride) microfiltration membranes.

The poly(acrylic acid)-graft-poly(vinylidene fluoride) (PAAc-g-PVDF) and poly(4-vinylpyridine)-graft-poly(vinylidene fluoride) (P4VP-g-PVDF) copolymers were obtained by thermally induced molecular graft copolymerization of acrylic acid (AAc) and 4-vinylpyridine (4VP), respectively, with the ozone-pretreated poly(vinylidene fluoride) (PVDF) in N-methyl-2-pyrrolidone (NMP) solution. Microfiltration (MF) membranes were prepared from the respective copolymers by phase inversion in aqueous media. The effects of pH of the coagulation bath on the physicochemical and morphological characteristics of the membranes were investigated. The surface compositions of the membranes were determined by X-ray photoelectron spectroscopy (XPS). The surface graft concentration of the AAc polymer for the PAAc-g-PVDF MF membrane increased with decreasing pH value of the coagulation bath. Completely opposite pH-dependent behavior was observed for the surface graft concentration of the 4VP polymer in the P4VP-g-PVDF MF membranes. A substantial increase in mean pore size was observed for the PAAc-g-PVDF MF membranes cast in basic coagulation baths of increasing pH. In the case of the P4VP-g-PVDF MF membranes, a substantial increase in mean pore size was observed for membranes cast in low pH (acidic) baths. The permeation rate of aqueous solutions through the PAAc-g-PVDF and P4VP-g-PVDF MF membranes exhibited a reversible dependence on the pH of the solution, with the membranes cast near the neutral pH exhibiting the highest sensitivity to changes in permeate pH.

Acrylates↗
PubMed1978

Vinyl chloride concentrations in maxillofacial prosthetics laboratories.

Air sampling was conducted in three maxillofacial laboratories to determine whether vinyl chloride, a carcinogen, was released during the formulation of polyvinylchloride facial prostheses. Results show that time-weighted average exposures of technicians were less than 0.1 ppm, a concentration meeting current U.S. Department of Labor standards.

Air↗
PubMed2002

Efficacy, cycle control, and user acceptability of a novel combined contraceptive vaginal ring.

OBJECTIVE: To assess the contraceptive efficacy, cycle control, tolerability, and user acceptability of a novel combined contraceptive vaginal ring for up to 13 cycles. METHODS: Healthy women requesting contraception were enrolled in this 1-year multicenter study. Each ring released 120 microg of etonogestrel and 15 microg of ethinylestradiol daily, and was used for 3 weeks followed by a 1-week ring-free period. RESULTS: A total of 2322 women started treatment and so formed the intent-to-treat population. Subjects were followed for 23,298 cycles, equivalent to 1786 woman-years. Compliance was good with 85.6% of cycles in full compliance with specified criteria. In the intent-to-treat population, 21 pregnancies occurred, giving a Pearl Index of 1.18 (95% confidence interval 0.73, 1.80). Eleven of the pregnancies were attributable to noncompliance; the Pearl Index for the per-protocol population was 0.77 (95% confidence interval 0.37, 1.40). The mean incidence of withdrawal bleeding was 98.5% in all cycles. Irregular bleeding occurred in 5.5% of all cycles, and in most women, early or late withdrawal bleeding was restricted to spotting. The ring was well tolerated with a low incidence of adverse events; only 2.5% of all discontinuations were device related. The ring was easy to insert and remove and did not interfere with intercourse. Eighty-five percent of women were satisfied with the ring, and 90% would recommend its use to others. CONCLUSION: The ring is an effective contraceptive with excellent cycle control that is convenient, well tolerated, and highly acceptable to users.

Adolescent↗
PubMed2002

Hydroperoxide lyase and divinyl ether synthase.

"Heterolytic" hydroperoxide lyase (HPL) and divinyl ether synthase (DES) are important enzymes of the plant lipoxygenase pathway. HPL cleaves fatty acid hydroperoxides into the aldehyde fragments. DES converts hydroperoxides into the divinyl ethers. The present paper is concerned with recent studies on HPL and DES including their occurrence, properties, mechanisms of action, the cloning of their cDNAs and physiological importance of the enzymes and their products.

Aldehyde-Lyases↗
PubMed1993

Microleakage of endodontic temporary restorative materials.

This study compared the sealing of Caviton, Cavit, and IRM at two powder to liquid ratios of 6 g/ml and 2 g/ml. Standard endodontic access preparations were made in 140 noncarious, nonrestored crowns of extracted human molars. They were divided into six groups, including positive and negative controls. Microleakage assessment was evaluated by basic fuchsin dye penetration after thermal cycling (5 to 55 degrees C for 100 cycles). The results indicated that Caviton provided the best seal, followed by Cavit. Cavit demonstrated better sealing than IRM at the powder to liquid ratio of 6 g/ml and 2 g/ml. There was a statistically significant difference in leakage between the Cavit group and IRM (powder to liquid = 6 g/ml), between the Cavit group and IRM (powder to liquid = 2 g/ml) group (p < 0.05). However, no statistically significant difference between the two different powder to liquid ratio groups of IRM was disclosed.

Analysis of Variance↗