Investigation of parameters affecting the supercritical fluid extraction of polymer additives from polyethylene

Polymer additives were extracted from polyethylene with supercritical carbon dioxide. The two-film theory, which considers mass transfer across a phase boundary, is applied to qualitatively describe the kinetics of mass transfer from the core of the polymer particles into the supercritical fluid extractant. The effects of pressure, temperature, addition of benzene as a modifier, properties and concentrations of the solutes, static time, and supercritical fluid extractant flow rate on the extraction process are investigated systematically. At constant temperature the extraction rates first increase with increasing pressure. When pressure reaches a certain level, a further increase of the pressure does not further increase the extraction rates. At constant pressure, the extraction rates were found to increase first and then decrease with increasing temperature. In addition to pressure and temperature, the SFE extraction kinetics is also influenced by the solute concentration, and the rate-limiting parameter in the extraction can be changed from solubility to diffusion during the course of the extraction. The magnitude of the effects of the experimental parameters depends on the properties and molecular weights of the solutes. The role of benzene as a modifier in the extraction of polymer additives from polyethylene is swelling the polymer particles and improvement of the solvent strength of the supercritical fluid extractant. Modifier effects were found to be more pronounced at lower temperatures

Application of the Retention Index Concept in Micellar Electrokinetic Capillary Chromatography. [Erratum to document cited in CA120:123851]

The errors were not reflected in the abstr. or the index entrie

Ionization mechanisms in capillary supercritical fluid chromatography-chemical ionization mass spectrometry

Ionization mechanisms have been studied for supercritical fluid chromatography (SFC) with mass spectrometric (MS) detection. One of the problems associated with SFC-MS is the interference of mobile phase constituents in the ionization process, which complicates the interpretation of the resulting mass spectra. This interference can be reduced by adding a reagent gas to the ion source. It was found that the properties and the pressure of this reagent gas control the ionization process. In this study ammonia was used as a chemical ionization (CI) reagent gas. An increase in the reagent gas pressure generally resulted in higher abundances of the protonated molecular ion. The presence of an excess of reagent gas suppresses charge exchange processes between the mobile phase constituents and the solutes. Charge exchange causes a more pronounced fragmentation than proton transfer in CI processes. The spectra obtained by charge exchange ionization, with helium as the reagent gas at moderately high pressures, are comparable to electron ionization spectra from standard MS libraries

The separation of herbicides by micellar electrokinetic capillary chromatography

A method for the sepn. of a no. of herbicides consisting of chlorophenoxy acids by micellar electrokinetic capillary chromatog. (MECC) was developed. SDS, Brij 35, cetyltrimethylammonium bromide (CTAB) and MeOH were introduced into the buffers to investigate their effects on the sepn. of the herbicides. SDS combined with Brij 35 as the micellar agent was found to provide the best overall sepn. of these component