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Addition of a small amount of polar solvent (i.e. modifier) which contains an ionic component (i.e. additive) to a CO2 mobile phase has shown major improvement in the elution of ionic analytes via packed column supercritical fluid chromatography (SFC). Firstly, we focused on the elution of sodium arylsulfonate analytes by using various ionic additives, such as lithium acetate, ammonium acetate, tetramethylammonium acetate, tetrabutylammonium acetate, and ammonium chloride. The analytes were successfully eluted with all additives with good peak shape under isocratic/isobaric/isothermal conditions. Three stationary phases with different degrees of deactivation were considered. They were conventional Cyanopropyl, Deltabond Cyanopropyl, and non-chemically bonded silica. The effect of additive concentration and additive functionality on retention was also investigated. Secondly, solid state NMR of the silica packing material before and after being flushed with supercritical CO2 modified by methanol containing the ionic additives was performed to gain some insight into the retention mechanism(s). A fraction of silanol protons were undetected after being treated with the mobile phase which suggested replacement by the cationic component of the additive. CaChe calculations were carried out on several of the additives in an attempt to explain why different ionic additives produce different effects on chromatographic retention. Modification of the stationary phase and ion pairing with the analyte are two possible retention mechanisms being considered. As ion-pair formation was considered to be one of the retention mechanisms, the use of sodium sulfonates as mobile phase additives to elute secondary and quaternary ammonium salts was then studied. Propranolol HCl, benzyltrimethylammonium chloride, and cetylpyridium chloride were chosen as the probe analytes. Sodium ethansulfonate, sodium 1-heptanesulfonate, and sodium 1-decanesulfonate were studied as mobile phase additives. The analytes were successfully eluted from Deltabond Cyano phase within 5 minutes, but were retained strongly without additive or with ammonium acetate as the additive. An Ethylpyridine column showed dramatic advantages on the elution of these ammonium analytes. No additive was required to elute these ionic compounds. Protonation of some fraction of the pyridine functional groups and the deactivation of active silanol sites were believed to be the major mechanisms responsible for this behavior. Lastly, we successfully eluted large peptides (up to 40 mers) containing a variety of acidic and basic residues in SFC. We used trifluoroacetic acid as additive in a CO2/methanol mobile phase to suppress deprotonation of peptide carboxylic acid groups and to protonate peptide amino groups. The Ethylpyridine column was used for the majority of this work. The relatively simple mobile phase was compatible with mass spectrometric (MS) detection. To our knowledge, this is the first report of the elution of peptides of this size with a simple, MS-compatible mobile phase. Fast analysis speed, the possibility of coupling multiple columns to achieve desired resolution, a normal-phase retention mechanism, and less use of organic solvents are the advantages of SFC approach for peptide separation. / Ph. D.

Supercritical fluid extraction (SFE) is an alternative to traditional extractions with organic solvents. SFE consists of removing the analyte(s) from the matrix, solubilizing them, moving the analyte(s) into the bulk fluid, and sweeping the fluid containing the analyte(s) out of the extraction vessel. As the fluid leaves the extraction vessel, decompression of the fluid occurs, changing its volume and temperature which can lead to analyte loss. This work focussed on the trapping process with the restrictor immersed in a liquid after SFE. Experiments compared the effects of trapping parameters on the collection efficiencies of fat-soluble vitamins of similar polarities and structures. The most important variable was the selection of collection solvent and its physical properties, such as viscosity, surface tension and density were found to be important. Additionally, adding a modifier to the collection solvent in an attempt to change its physical properties and influence collection efficiencies for a polarity test mix was studied. Addition of a modifier can improve collection efficiencies and allow higher collection temperature to be used, but the modifier did not increase trapping recoveries to the extent that collection pressurization did. The occurrence of a methylation reaction of decanoic acid during the SFE and collection processes, using a methanol modified fluid or collection solvent was investigated. The majority of the reaction occurred during the collection process and the degree of methylation was found to be dependent on temperature, but not on static or dynamic extraction time. When no additional acidic catalyst other than carbon dioxide in the presence of water was present, conversion was limited to about 2%, but was quantitative with an added acidic catalyst. The last portion of this work involved the application of the SFE process to the extraction and analysis of extractable material in eight hardwood and softwood pulp samples. Grinding the samples increased extractable fatty acid methyl esters (FAMEs) by ten-fold, and in-situ derivatizations resulted in higher FAME recoveries than derivatization after SFE. Liquid trapping enhanced recoveries of lower FAMEs when compared to tandem (solid/liquid) trapping. In-situ acetylations sometimes yielded acetylated glucoses. Large differences in FAMEs concentrations were seen for hardwood samples, but lesser differences were seen for the softwood pulp samples. / Ph. D.

The need for sensitive and selective detectors in supercritical fluid chromatography (SFC) is particularly evident since SFC can be used to analyze classes of compounds that are not readily amenable to either gas chromatography (GC) or liquid chromatography (LC). These compounds include species that are nonvolatile or thermally labile and , in addition, contain no chromophore that can be used for spectrophoto detection. The objective of this research is therefore to interface selective chemilumninescent detectors with SFC in the sensitive detection of nitrogen- and/or sulfur containing compounds. The chemiluminecent nitrogen detector (CLND), a gas-phase detector which is specific for nitrogen-containing compounds, was first evaluated as a detector for use with capillary SFC. The potential use of the CLND for food flavor and petroleum samples was demonstrated. In addition to equimolar nitrogen response, the CLND showed good sensitivity and large linear dynamic range. Minimum detectable quantity (MDQ) was 60 pg of nitrogen with a linear range of over 3 orders of magnitude. Nitrogen to carbon selectivity of 105 was obtained. Capillary SFC with simultaneous flame ionization and chemiluminescent detection was also demonstrated. The second portion of the research investigated the CLND for packed column SFC with methanol modified CO2. The only modification made in the CLND for packed column SFC is the pyrolysis furnace. The CLND and UV were used to interface with SFC via a post-column split. Methanol-modified CO2 was also demonstrated to be compatible with the CLND even with a high mobile phase flow rate. The use of pressure and modifier programs appears to be feasible as is evidenced by the baseline studies which have been performed, as well as by the applications demonstrated. The last portion of the research focused on the evaluation of a new generation sulfur chemiluminescent detector (SCLD), which is also a gas-phase detector, with packed column SFC using both pure and methanol modified CO2. The minimum detectable quantities were determined to be 2.6 pg or 14 pg sulfur for mobile phase employing pure CO2 or 8% methanol modified CO2 respectively. The evaluation study also showed excellent selectivity and linearity, as well as day-to-day repeatability. The capabilities of the SFC-SCLD system for sulfur speciation and detection of thermally labile pesticides and polar sulfonamides, as well as petrochemical samples were presented. / Ph. D.

A method has been developed for the quantitative extraction of nitrotoluenes (2,6-dinitrotoluene, 2,4-dinitrotoluene, and trinitrotoluene) from water. Three types of solid sorbents were investigated: two 47 mm Empore disks™ - octadecylsilane (C18) and styrene-divinylbenzene (SDVB); and one Bakerbond spe*™ Phenyl stationary phase. The phenyl sorbent yielded the highest recoveries. The average SPE recoveries for spike standards ranged from 80 to 95 percent for Millipore water and 55 to 95 percent from well and surface water in the low ppb and ppt levels. After the nitrotoluenes were trapped on the solid sorbents they were quantitatively eluted by first doping the bed with toluene and then extracting with supercritical carbon dioxide. Doping with toluene was found to increase the rate of extraction. The extracts were analyzed off-line via GC-ECD using an internal standard. Extraction losses are due to analyte break through, and not from poor SFE recoveries. This demonstrates that supercritical fluid extraction is a suitable elution technique for analytes trapped on solid phase extraction (SPE) cartridges. A method has also been developed and evaluated for the direct on-line coupling of SPE to GC. SPE-SFE-GC-ECD analysis eliminates off-line collection and subsequent handling of hazardous materials. SFE is an ideal means of directly coupling SPE to GC, since carbon dioxide is a gas at ambient temperatures and pressures and thus easily removed. One potential problem for SPE-SFE on-line GC is the presence of residual water trapped on the active sites of the bonded silica sorbent. The presence of water can interfere with the cryogenic trapping of the analytes on the capillary GC column. The water becomes ice at cryogenic temperatures and in large quantities blocks the GC column. This problem has been avoided by using a split injection interface previously described by Hawthorne. The quantitative reproducibility of this interface will be investigated for nanogram quantities of nitroaromatics. / Ph. D.

In this work the Supercritical Fluid Extraction (SFE) and detection of sorbed metals in contaminated soils is explored. Iron containing samples were spiked onto sea sand and extracted with Supercritical Fluid CO₂. On-line detection was accomplished by decompressing the SF-CO₂ and analyte into a microwave induced plasma, whereby the resulting Iron atomic emission signal was quantified. This dissertation reports the first successful coupling of SFE and Microwave Induced Plasma - Atomic Emission Detection (MIP-AED) for the on-line analysis of sorbed metal contaminants. The on-line analysis was accomplished with a novel SFE-MIP interface design. Experiments involving the on-line extraction and detection of ferrocene spiked sea sand were very promising, in that unity of extraction and detection was achieved with this nonpolar compound. Percent recovery was greatly reduced when the on-line extraction of Iron III Trifluoroacetylacetonate (FeTFA) was attempted. Off-line extraction studies were performed to establish the optimum conditions necessary to effect the SFE of the following Iron III complexes: Iron III Acetylacetonate (FeAcac) and Iron III Trifluoroacetylacetonate. The greatest recovery (55.85 0/0) was achieved with Supercritical Fluid-CO₂ under the following conditions: 60°C, 150 atm, 20 minute static extraction followed by 20 minute dynamic extraction. The extraction vessel contained 0.250 mg iron complex, 20 μL HPLC grade methanol, and 20 μL deionized water. Trapping of the analyte was achieved by decompressing the SF-CO₂ and analyte in 10 mL of HPLC grade methanol held at O°C. / Ph. D.