Document Type

Dissertation - Open Access

Award Date

2016

Degree Name

Doctor of Philosophy (PhD)

Department / School

Chemistry and Biochemistry

First Advisor

Douglas Raynie

Abstract

Supercritical fluid extraction (SFE) technology has been well received as an environmentally friendly processing technique. Over the last two decades, its use in many processing industries has tremendously advanced. This is as a result of pressure from regulating bodies aimed at reducing the wide-scale use of organic solvents due to negative environmental impacts. Supercritical carbon dioxide (SC-CO2) is considered to be environmentally benign and has been used in the development of a wide-range of alternative processes in various industries to totally or partially eliminate the use of organic solvents. Conventional processes for essential oil extraction involve steam distillation and organic solvent extraction. Steam distillation involves high heat, which can cause sample hydrolysis and thermal degradation of heat-sensitive compounds, whereas in organic solvent extraction, polluting solvents and expensive post-processing of the extract for solvent elimination is involved. SFE can be divided into two major stages, the extraction of the analyte of interest from the bulk matrix and the collection of the analyte. There has been a lot of research on the optimization of analyte extraction. However, researchers have largely ignored the collection stage. To achieve high analyte recovery and extraction efficiency in SFE, the extraction step and subsequent collection step should be considered integrated. This dissertation focuses on a comprehensive study, using the response-surface methodology experimental design approach, of the collection of volatile compounds following supercritical fluid extraction (SFE) and application to the extraction of essential oils from selected plants found in the Great Plains region which are of interest to ethnobotany colleagues. Parameters that influence the collection of the extract after SFE by trapping with a small volume of an organic solvent were investigated. Time, depressurization flow rate, cooling temperature, solvent type, and analyte type were found to be the most important factors affecting trapping. The optimal collection conditions for the three solvents considered in the study were isopropanol (25.58 min, 2.07 oC, and 0.3 L/min), acetonitrile (28.30 min, -8.20 oC, and 0.3 L/min), and dichloromethane (26.8 min, 3.21 oC, and 0.3 L/min). The amount of solvent was found to be significant in less viscous solvents and insignificant in viscous solvents. Cooling position and restrictor position were found to be insignificant. In the extraction of essential oils from Chrysothamnus nauseosus (rabbit brush), Rhus aromatic (skunk brush), and Matricaria chamomilla L (chamomile), pressure, time, and temperature were found to be the most significant extraction parameters. In Chrysothamnus nauseous (rabbit brush) the major compounds identified by GC-MS were limonene (35.77%), trans-β-ocimene (27.41), camphor (11.57%), β-phellandrene (4.64%), β-pinene (4.13%), eucalyptol (2.20%), β-cis-ocimene (2.66%), camphene (1.96%), and artemiseole (1.61%). In Rhus aromatic (skunk brush) the main compounds were limonene (20.48%), linalool (37.31%), caryophyllene (12.5%) eucalyptol (9.14%), α-phellandrene (5.5%), and geraniol (1.2%). In chamomile samples from three different regions in Kenya were α-bisabolol, α-bisabolol oxide B, α-bisabolol oxide B, matricine, dicycloether, and β-cis-farnesene. The optimal extraction conditions (temperature, pressure and time) for chamomile, rabbit brush, and skunk brush oils were (47 oC, 6620 psi, 45 min), (37 oC, 1720 psi, 43 min), and (35 oC, 3570 psi, 40 min) respectively. Selected major essential oils identified in the different samples were quantified. α - Bisabolol concentrations in Kangari, Kibwezi, and Njabini chamomile sample were 1.03±0.006 mg/g, 0.759±0.092 mg/g, and 0.90±0.011 mg/g respectively. Limonene and camphor concentrations in rabbit brush were 2.052±0.020 mg/g and 0.652±0.010 mg/g respectively. Limonene, linalool, and caryophyllene concentrations in skunk brush were 1.448±0.027 mg/g, 2.28±0.014 mg/g, and 0.956±0.018 mg/g.

Library of Congress Subject Headings

Supercritical fluid extraction.

Essences and essential oils.

Plant extracts -- Analysis.

Natural products.

Environmental chemistry.

Description

Includes bibliographical references (page 117-131)

Format

application/pdf

Number of Pages

149

Publisher

South Dakota State University

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Chemistry Commons

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Rights Statement

In Copyright