Effect of Solvent and Temperature on Extraction of Polychlorinated Biphenyls and Polychlorinated Dibenzodioxins From Fly Ash

Abstract

The aim of this work was to understand the crystallization process of terfenadine in solution. Cooling of saturated solutions prepared at 50 • C at different temperatures, evaporating the solvent from nearly saturated solutions at a certain temperature, and exposing ethanol solutions of terfenadine to water vapour atmosphere were the techniques used for obtaining terfenadine specimens. The characterization of these specimens was carried out by thermal microscopy, differential thermal analysis, thermogravimetry and powder X-ray diffraction. Crystalline phases, amorphous solids, and solvates were identified. For the solvents used in the present study, the crystallinity degree of terfenadine decreases from ethanol-water to ethanol and from this to methanol. Decreasing the temperature promotes the formation of amorphous solid material; at low temperatures, methanol and ethanol solvates are also formed. Desolvation, following the terfenadine aggregation process in solution accounts for the different behaviour found for the solvents and for the effect of temperature on the structure. The role of the solvent as structure-mediator is explained on the grounds of the values previously published for the enthalpy of solution of terfenadine in the solvents under study.

Microwave-Assisted Extraction of Polychlorinated Biphenyls and Polychlorinated Dibenzodioxins From Fly Ash

“…Increased recoveries were not observed between 100 and 110 C. Our previous paper also reported higher recoveries of PCBs and PCDDs using PFE and EFLE from fly ash at 100 C (15). Therefore, it can be suggested that the optimum temperature is independent of the extraction methods as the same temperature is also optimal for MAE, just as 100 C is suitable for PFE and EFLE.…”

“…After the extractions, the quantification of the extracts could not be carried out without multi-layer silica gel column clean-up (Figure 1 (A)); chromatographic interferences made quantification inaccurate (Figure 1 (B)). It has been previously reported that interferences could be removed using multi-layer silica gel column clean-up (11,12,15,16).…”

Análisis de la calidad del aire en el interior de edificios

“…Los sistemas de medida de muestreo sobre soporte, ya sea sólido o líquido, y posterior análisis en laboratorio, generalmente por cromatografía de gases/espectroscopia de masas, son técnicas baratas, sobradamente contrastadas, y que han dado muy buenos resultados analíticos, siendo usadas como principal medio de análisis durante años [95], [96], [97]. Sin embargo, esta técnica tiene sus límites:…”