1,721,139 research outputs found
CORRELATIONS BETWEEN BALTIC AMBER AND PINUS RESINS
No full textThe composition of the acid fractions of four pine resins has been studied before and after an 'ageing' process. Correlations are established between Baltic amber and 'aged' Pinus halepensis resin. © 1985
Hydrogen-treated graphitized carbon blacks. Limiting isosteric heats and entropy changes upon adsorption of hydrocarbons
No full textThe study of the effects of hydrogen treatment at 1000° on graphitized carbon blacks was extended to the adsorption of nonpolar molecules. Before and after the hydrogen treatment on the Graphon and graphitized Sterling FT (Sterling FT-G) surfaces, the isosteric heats and entropies of adsorption at extremely low surface coverages of ethane, propane, isobutane, butane, pentane, and hexane were determined by chromatography using the eluted pulse technique. Our results were compared with some earlier determinations obtained by chromatography or by static methods. The abnormally high limiting heats and entropy changes of adsorption on untreated Graphon indicated the presence of a small fraction of surface geometric irregularities, where the interaction of an individual adsorbed molecule occurs with more than one plane of'the adsorbing surface. Some experimental data suggest that surface heterogeneities can be identified as cavities with specific dimensions. These irregularities are not found on the Sterling FT-G surface, which we observed as almost completely free of strong adsorption sites. After the hydrogen treatment, the heats and entropy changes of adsorption on Graphon sharply decreased and their values are almost equal to those measured upon adsorption on Sterling FT-G. This agreement shows that the hydrogen treatment is effective in removing not only traces of surface oxides but also topographical irregularities on the carbon surface. The standard integral adsorption entropy values were calculated from retention volume measurements and by using a relation we derived. The close agreement between our values and those derived by a static method makes it evident that the gas chromatography technique can definitely also be of great use in the determination of adsorption entropies at very low surface coverages
Determination of trace amounts of C2-C5 acids in aqueous solutions by gas chromatography
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Hydrogen-treated graphitized carbon blacks
No full textAbstract The isotherms and isosteric heats of adsorption in the region of very low surface coverages have been measured for propylamine and acetic acid on two graphitized carbon blacks, graphitized Sterling FT and MT, before and after hydrogen treatment at 1000°. In order to obtain adsorption isotherms at very low coverages with good precision, a gas chromatographic method has been adopted. The experimental results confirm the effectiveness of the hydrogen treatment in removing trace amounts of surface oxides and the usefulness of an oxygen-free carbon surface in deriving adsorption isotherms of hydrogen-bonding substances. The removal of chemical impurities causes the extent of propylamine adsorption to be sharply reduced and the shape of the isotherm to be altered. On untreated graphitized carbon blacks, the heat of adsorption of propylamine shows an uninterrupted fall as the surface coverage increases, whereas after the hydrogen treatment, a constant value of 7.5 kcal/mole is obtained. In contrast to the behaviour of propylamine, on treated carbon surfaces the adsorption of acetic acid increases and the heat-coverage curve is steeper than for untreated surfaces. This is because the adsorbate can establish strong lateral interactions on a clean surface. The surface density of chemisorbed oxygen on unpurified graphitized Sterling FT is estimated as two oxygen-containing groups per 104 A2
Extraction and isolation of phenoxy acid herbicides in environmental waters using two adsorbents in one minicartridge
No full textGas-liquid-solid chromatography-theoretical aspects and analysis of polar compounds
No full textAdsorptive modifications on graphitized carbon blacks, (graphitized Sterling FT and Graphon) carried out by deposition of polymeric macromolecules of polyethylene glycol 1500 (PEG 1500) have been evaluated by increasing the surface concentration of PEG 1500 up to the formation of a few layers on the adsorbing media. The role played by both the liquid and the solid medium in the sorption process of vapors has been investigated by measuring heats, entropies, and capacity ratios for some polar and nonpolar eluates at various liquid/solid ratios. Experimental evidence is given for the occurrence of multilayer adsorption of macromolecules of PEG 1500 on the graphitized carbon surface. A simple, chromatographic criterion is suggested to evaluate the completion of the first layer of the liquid phase. The great usefulness of liquid-coated solids in the chromatographic analysis has been made evident by evaluating gas-liquid-solid columns in terms of selectivity, efficiency, and thermal stability. Also, the high performance of such columns has been exploited in the elution of some interesting, very dilute aqueous solutions of polar compounds
High-Molecular Polyethyleneimine Coated Graphitized Carbon Black for Trace Determination of Strong Organic Bases
No full textAbstract Tailing-free peaks even at the sub-nanogram level for amines have been obtained by using graphitized carbon black (GCB) as packing material modified with suitable amounts of KOH and a high molecular polyethyleneimine (PEI 40 M). This kind of column packing has been evaluated in terms of selectivity, retention time, efficiency and thermal stability. By the use of 1% PEI + 0.3% KOH modified GCB a clean chromatographic profile has been obtained for a C1 to C4 aliphatic amine water mixture, containing 1 ppm of each compound. Well-separated and well-defined peaks for a 0.5 ppm methylamine, dimethylamine, trimethylamine aqueous solution have been obtained within 1 min of elution time by decreasing the amount of PEI to 0.5%. Also, separations of ether solutions either of diamines or amphetamines have been exploited on a 1.5% PEI 40 M + 0.3% KOH + GCB column
Bioaccumulation of LAS in feral fish studied by a novel LC-MS/MS method
No full textThe extent of bioaccumulation of linear alkylbenzene sulfonate (LAS) in feral organisms is presently unknown. To enable LAS determination in biota samples, LAS and its coproducts (methylbranched LAS, dialkyltetralin sulfonates) are extracted from tissues using matrix solid-phase dispersion, isolated by strong anion exchange chromatography and determined by HPLC-electrospray-tandem mass spectrometry. All analytes were quantified in sediment dwelling Tubifex so. with the sum of the concentrations exceeding 1 mumol/g. Since a portion of LAS was present adsorbed to solids in the guts, the actual body residue was lower than reported lethal LAS body residues. The concentrations of individual constituents in bream muscle samples from the river Saar and fathead minnows caged in the river Arrone ranged up to 2 nmol/g. The apparent bioaccumulation factors in the caged fish are consistently higher than laboratory data, presumably due to a combination of LAS present in the guts adsorbed to suspended material, coingestion of LAS with bacterial detritus, and depressed metabolic activity due to sublethal effects. Given the small deviation between laboratory and field bioaccumulation data and the high detection frequency (>90%) of C-13-2- and C-13-iso-LAS, the latter two constituents are suitable markers for LAS contamination in fish
Selective determination of phenols in water by a two-trap tandem extraction system followed by liquid chromatography
No full textThe ability of a two-trap tandem system, one containing 300 mg of graphitized carbon black (GCB) and the other filled with 50 mg of Sephadex QAE A-25 strong anion exchanger (SAX), to extract trace amounts of phenols from environmental waters and isolate them from base-neutral species was evaluated. After the water sample had passed through the GCB cartridge, the latter was connected to the SAX cartridge and base-neutral species were removed from the GCB surface by a neutral eluent. Co-eluted very weakly acidic phenols were selectively readsorbed on the SAX surface. Still maintaining the two cartridges in series, an acidified eluent was allowed to flow through the two cartridges to recover the most acidic phenols from the GCB cartridge and the least acidic phenols from the SAX cartridge. After partial removal of the solvent, the final extract was submitted to reversed-phase high-performance liquid chromatography with UV detection. Recoveries of seventeen phenols of environmental concern added to 2 l of drinkgin water at levels between 0.2 and 2 μg/l were higher than 90%. The effect of the presence in water of fulvic acids on the efficiency of the extraction device was assessed. In term of recovery, the two-trap tandem system was compared with other two single extraction cartridges, one containing a chemically bonded siliceous material (C18) and the other SAX material. The limits of detection of the analytes considered were well below 0.1 μg/l
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