| The research described herein addresses: (a) new high-resolution methods for the determination of PCBs in a variety of freshwater biological samples, with the goal of congener-specific determination; and (b) the proof of concept for a novel absorption spectrometer designed for use with path-length-limited separation methods.; While most methods that have been developed for PCB determination focus on a single organism, our research showed that careful consideration must be paid to the methods used for determination because several species showed significant retention time changes using standard methodologies. Several congeners in certain biological species drifted in retention time by one minute or more, with the possibility of as many as fifteen other congeners eluting within the same retention time window. Our interpretation of these changes is that there is likely a complicated influence introduced by matrices and interactions with the stationary phase that is dependant upon the species being investigated.; The separation of the 209 possible polychlorinated biphenyl (PCBs) congeners is one of the most challenging determinations in the quantitation of semi-volatile organic compounds (SVOCs). We therefore developed a new method using electron impact ionization coupled to gas chromatography-tandem mass spectrometry (GC-MS/MS) for improving the determination of the total PCB concentrations in 20 extracts from a variety of freshwater species. The PCB homolog classes are divided into three groups for each chromatographic run, resulting in a series of three injections for each extract. The method has a 99% confidence in minimizing false-positive congener quantitation that is the result of the extensive fragmentation of higher homologs to resemble lower homologs in the mass spectrum.; Finally, a prototype Photon Trapping System (PTS) was designed and fabricated to address the improvement in the path-length for chromophores with low molar absorptivity. The instrument contains an optical cavity to trap photons, bounded by a pair of high-reflectivity mirrors. The mirrors are designed with narrow slits that radiate from the center, and when operated at high rotational frequency, permit packets of photons to enter the cavity, become trapped between the spinning mirrors, and then exit to the detector. A theoretical model was also developed to describe the enhancement of path-length as a function of the angular velocity of the mirror, cavity width, path length, and offset angle between mirror slits. For fabrication of the prototype, off-the-shelf system components were an Ar ion LASER source, high-speed motor for the spinning mirrors, and photo multiplier tube detector. The spinning mirrors, axle, and motor mount were designed, constructed, and tested, as well as a sample delivery system using a co-axial nozzle. In addition, the prototype shows promise for path-length-limited techniques such as for the mum path-lengths that are required in capillary electrophoresis (CE). A sample delivery nozzle was designed and coupled to a permeation tube for the generation of gas-phase standards. Demonstration of the prototype with nitrogen dioxide as the initial test analyte is discussed. |
