Off-campus UMass Amherst users: To download dissertations, please use the following link to log into our proxy server with your UMass Amherst user name and password.
Non-UMass Amherst users, please click the view more button below to purchase a copy of this dissertation from Proquest.
(Some titles may also be available free of charge in our Open Access Dissertation Collection, so please check there first.)
Analytical studies in supercritical fluid technology: Investigation of photoionization detection in solvent-modified supercritical fluid chromatography. Phosphite antioxidant characterization in low density polyethylene using coupled supercritical fluid extraction and chromatography
Abstract
In the first part of the dissertation, single photon, gas phase photoionization detection in conjunction with supercritical fluid chromatography (SFC) was investigated with respect to the effects of using methanol-modified carbon dioxide mobile phases on detector performance and analytical figures of merit. The presence of relatively small amounts of methanol in the base supercritical fluid was found to result in substantial reductions in analytical sensitivity due to increased electron capture-mediated quenching of photoions and increased excitation source absorption. Reduction of ion chamber concentrations of modifier using argon make-up gas provided analytical sensitivity improvement ranging between 44 and 200%. Theories were developed to account for the increase in photoionization background signal during pressure-programmed SFC. In addition, difficulties in interfacing the photoionization detector with the SFC system were overcome due to the development of an electrolysis-based stainless steel restrictor fabrication technique. In the second part of the dissertation, coupled supercritical fluid extraction and chromatography (SFE/SFC) was used to characterize phosphite antioxidants and their degradation products in low density polyethylene (LDPE). A novel self-cryofocusing interface for coupled SFE/SFC which does not rely upon external cooling and allows the analytes to be delivered to the SFC column by direct dissolution in the supercritical mobile phase was developed and implemented for the additives characterization research; the apparatus was found to provide excellent analytical mass sensitivity using 1 milligram samples. SFE of single polyethylene pellets revealed that representative sampling was insured only by grinding multiple pellet lots. By comparing the SFE approach with that of conventional liquid-based extraction and characterization techniques such as reflux extraction followed by HPLC analysis, SFE/SFC was found to be competitive in terms of both analytical recovery and accuracy. Results indicated that both analytical reproducibility and sample processing time could be optimized by increasing the sample surface area-to-weight ratio.
Subject Area
Analytical chemistry
Recommended Citation
Davis, Mark Sebelon, "Analytical studies in supercritical fluid technology: Investigation of photoionization detection in solvent-modified supercritical fluid chromatography. Phosphite antioxidant characterization in low density polyethylene using coupled supercritical fluid extraction and chromatography" (1991). Doctoral Dissertations Available from Proquest. AAI9207383.
https://scholarworks.umass.edu/dissertations/AAI9207383