The retention behaviour and separation of some water-soluble organophosphorus insecticides on polyester-based polyurethane foams.
This paper reports the concentration of some dissolved organic phosphorus insecticides in water by open-cell polyurethane foam. The results of preliminary screening tests on the retention of the tested insecticides (Diazinon, Malathion and Chloropyrifos) by polyester foams indicated that a very high percent removal of the insecticides was obtained. The retention rate was fast and reaches equilibrium in a few minutes. The various parameters affecting the preconcentration of the tested insecticides by unloaded foam, e.g. pH, extraction media, shaking time, salt effect, flow rate, temperature and sample volumes have been optimized via the static mode of separation. The unloaded foams were employed in columns for the retention and recovery of the tested species. The sorption efficiency and the recovery of the tested compounds by the unloaded foam column were found to be up to 95.5%. The equivalent to a theoretical plate by the unloaded foam was found in the range 1.12 - 1.32 +/- 0.2 mm. The sorption mechanism of the tested species by the foam is discussed. The separation of some of the tested species in a mixture was achieved. The foam membrane offers unique advantages over conventional bulk-type granular sorbents and solvent extraction in offering high flow rates, rapid, versatile, effective separation and preconcentration of different species from aqueous samples. The foam provides the advantages of being, insoluble, easily separable and non-polluting, as well as inexpensive.
Retention and separation of some organic water pollutants with unloaded and tri-n-octylamine loaded polyester-based polyurethane foams.
The analytical utility of unloaded and polyester-based polyurethane loaded foams with tri-n-octylamine (TOA) in the removal of some phenols from water were carried out. In static mode, the TOA-loaded foams showed a good affinity of extraction towards the tested compounds as compared to the untreated foams. The various parameters affecting the retention efficiency of the tested compounds from aqueous media by the foam were examined via batch technique. The TOA-loaded foams were employed in column modes for the extraction and recovery of the tested phenols. The retention efficiency and the recovery of the tested compounds from the loaded foam column were up to 98.5%. Sorption of the compounds by the foam were brought by solvent extraction mechanism. The molecular weight and the pK(a) of the compounds play an important role in the extraction process. The height equivalent to a theoretical plate (HETP) of the TOA-foam column was found in the range 1.8-2.05 +/- 0.1 mm at flow-rates up to 10 cm(3)/min. Separation of some of the tested phenols was also carried out by the TOA-foam columns. The membrane properties of the polyester foam sorbents give unique advantages over conventional granular sorbents in rapid, versatile and effective separations and preconcentrations of the tested compounds.
How Does the Keyword Method Affect Vocabulary Comprehension and Usage? Report from the project on Studies in Language: Reading and Communication. Working Paper No. 278.
THE KEYWORD METHOD of vocabulary learning involves forming a linkage between a to-be-learned vocabulary word and a familiar English word that sounds like part of the to-be-learned item (the keyword). Then the learner forms an interactive image between the keyword and definition referents. In previous research, the keyword method has been found to facilitate students' recall of definitions, given vocabulary items. In this study, use of the method was also shown to increase comprehension of English vocabulary in context, as well as usage of that vocabulary in a novel context.