Browsing by Author "Messer, Dale C."

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    Evaluation of conditions for quantitative recovery of a drug from animal feed using supercritical fluid CO₂ extraction
    Messer, Dale C. (Virginia Tech, 1991)
    Supercritical fluid extraction (SFE) continues to be explored as a feasible alternative to traditional Soxhlet and other types of extraction. In many cases SFE is cleaner, faster, and less expensive than the traditional types of extractions. This investigation has focused on the evaluation of Supercritical CO₂ extraction as a quantitative method for recovery of a hypolipidemic drug (tradename xenalipin) from an animal feed matrix. Initial emphasis of this study focused on the recovery of xenalipin from a the animal feed matrix employing a liquid solvent trap. By studying the effect of time of extraction versus recovery of drug, the liquid trap was shown to be inadequate. Further studies implemented the extraction of xenalipin from a filter paper matrix and the use of solid phase traps. This method of inquiry was use to evaluate the degree of recovery as related to the parameters of CO₂ density, extraction time, and flow rates of CO₂. After achieving quantitative extraction of xenalipin from filter these parameters were transferred to the animal feed matrix. The animal feed matrix was prepared using three different methods. Each matrix was evaluated for homogeneity of sample and ability to achieve quantitative extraction.
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    Supercritical fluid extraction of non-traditional matrices
    Messer, Dale C. (Virginia Tech, 1994)
    Supercritical extraction (SFE) has most often been linked to the use of modified or unmodified CO₂ for the recovery of relatively non-polar analytes from solid matrices. The objective of this research was to expand current supercritical fluid (SF) techniques to the recovery of analytes from non-traditional matrices. SFE with three unique matrices was completed. Small mammals are often used in drug toxicity studies. Pharmaceutical dosage verification in the animal feed is a requirement in these studies. Atovaquone, a drug used in the treatment of aids related pneumonia, was successfully recovered from rat feed with supercritical CO₂. Drug recoveries of ≥ 90% were achieved with a range of drug concentrations from 0.03% to 1.1% in the feed. The second phase of the investigation studied the recovery of acyclovir, an antiviral agent, from Zovirax® 5% ointment. This recovery required a radically different approach from all previous SFE techniques, as the analyte was completely insoluble in the supercritical fluid. This unique situation led to the development of "Inverse SFE", where the ointment matrix was extracted and the drug analyte was retained in the extraction vessel. Included in the investigation were the effects of temperature, modifier, drug recovery techniques and length of extraction. Employing a 20 minute inverse SFE, 99% of the acyclovir was recovered from the ointment. Increasing regulation, disposal costs and environmental issues have fueled concerns over the use of chlorinated organic solvents. Currently, over 50% of the samples regulated by the EPA have liquid matrices that have been traditionally analyzed using these solvents. The implementation of solid phase extraction (SPE) has significantly reduced the amount of organic solvent utilized for the extraction of liquid matrices; however, further reduction is desired. The third phase of this work concerned the elution of a SPE disk with SF wherein the disk had been used to concentrate pollutants from fresh and brackish water. Initially, this research focused on the quantitation of polyaromatic hydrocarbons (PAHs) from distilled water. The analytes were deposited onto a solid phase extraction disk and eluted with a SF. The proper method of quantitation, relative versus absolute, was also investigated. Optimization of the SF elution in relation to time, temperature, flow rate, and pressure while maintaining quantitative recoveries was performed. A three step, 27 minute SF elution method resulted from this effort. Recoveries were ≥ 90% for all the 16 PAHs studied. A chamber temperature of 80°C with liquid flow rate of 2 mL/minute was employed. The study was expanded to 39 EPA Method 525.1 analytes in distilled water. Although system contamination proved to be a problem, all but four analytes were quantitatively recovered according to EPA criteria. SF elution studies of brackish water matrices from the Chesapeake Bay indicated suspended sediment was responsible for water retention on the surface of the SPE disk. The retained water interfered with analyte recovery. More thorough drying techniques resulted in the recovery all but five analytes meeting EPA criteria.