Adsorption / Desorption and Preconcentration of Organophosphate Pesticides and Plasticizers with Humic Fraction-Immobilized Silica Gel in Hexane
| Autor: | Yan-Shuo Lai, 賴衍碩 |
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| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 102 Fractions collected from humic acid (HA) under acidic conditions and used as adsorbents for various agricultural organophosphate pesticides and phosphate-based plasticizers in hexane are immobilized on silica gel. For most organophosphate and phosphate-based plasticizers analytes examined in this study under the same conditions, the percentage of adsorption achieved nearly 100%, or above 90% respectively in 1 h, and was found to be highly relevant to the structure of the analyte and the type of interaction that occurred between the functional groups attached to it and HA. The interaction leading to adsorption between the functional moieties of the analyte and HA (in the case of organophosphate pesticides, P－O or S bond of analyte vs. carboxyl group of HA; in the case of plasticizers, the carboxylate group of analyte against the carboxyl group of HA) is believed to be reversible and dipole-dipole oriented, and is significantly enhanced in hexane. The enhancement of π-π interaction, even hydrogen bonding in some cases, was also observed in hexane and contributed to the percentage of adsorption to a certain degree. However, the interaction is subject to the steric hindrance effect caused by the bulky group or element surrounding the phosphorus element for organophosphate pesticides and the bulky alkyl groups attached to ether linkages and the relative position of the two ether bonds on the aromatic moiety of the analyte for plasticizers. Considering the nature of the analyte, the time required to reach the maximum percentage of adsorption is decreased as the amount of adsorbent is increased. Furthermore, the adsorption process is surface-oriented because the longer the time that is elapsed, the higher the percent of the analyte that is adsorbed. Factors such as the acidic or basic origin of the additive in the liquid phase of the matrix also affect the adsorption percentage of analyte. None of these results was reproducible or observable when using other organic solvents, such as ether, or when performed in an aqueous environment. The pre-concentration of the analyte and, thus, the recycle of the adsorbent can be achieved by adsorbing and, subsequently, desorbing it in a different solvent, such as acetonitrile. The recovery rate obtained in acetonitrile for several selected plasticizers analytes was higher, indicating that the adsorption process was highly specific and reversible. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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