| To extend the usefulness of low resolution desorption chemical ionization desorption chemical ionization-mass spectrometry (DCI-MS), an analytical method was developed that permitted the use of mass deficient reference standards for calibration purposes in accurate mass measurements of positive ions under ammonia DCI conditions. This was accomplished by employing a mixture of ammonia and methane as reagent gases. In the high resolution accurate mass measurement experiment, this gas mixture allows for simultaneous detection of the mass spectrum of perfluorokerosene (calibration substance) adequate for calibration purposes, and the spectrum of the analyte which contains molecular weight information.; Both low and high resolution DCI-MS were used to identify arsenic compounds present in Mytilus californianus. The mass spectrometric techniques described above were used to analyze the purified materials and provide spectra suitable for the structural characterization of two principal arsenic species present in the mussels; arsenobetaine (AsB) and the tetramethylarsonium ion.; Hydride generation-gas chromatography-mass spectrometry (HG-GC-MS), developed in this work, was used to provide conclusive evidence of -CD{dollar}sb3{dollar} incorporation from L-methionine-methyl-d{dollar}sb3{dollar} into arsenic compounds produced from arsenate by alga cell cultures. These findings strongly support the notion that the oxidation-reduction pathway involving carbonium ions, as originally suggested by Challenger for the alkylation of arsenic by microorganisms, applies to marine unicellular alga and probably other marine organisms.; Micro-liquid chromatography (LC) columns (0.32 mm inner diameter) fabricated and packed in house can be conveniently coupled on-line to a variety of mass spectrometric systems, mainly because of the extremely low flow rates they require. It was shown that a 99% reduction in the volume of solvent waste is achieved by switching from conventional to micro-LC, and a 87.5% reduction by switching from microbore to micro-LC.; The micro-LC columns are able to efficiently separate arsenicals that are used as animal feed additives as well as their potential metabolites.; Simplex optimization was used to efficiently delineate the optimum experimental conditions to be used for the electrothermal atomic absorption spectrometric analysis of arsenic in a standard reference material of marine origin. Four experimental variables, were considered: ashing temperature, atomization temperature, modifier concentration, and atomization ramping time. This combination of methods and materials provides a powerful means of rapidly optimizing the experimental conditions used for the analysis of arsenic in a wide variety of samples of environmental origin. Excellent recoveries of arsenic were obtained when using the optimum electrothermal atomic absorption spectrometry conditions to analyze standard solutions of arsenobetaine, arsenocholine and tetramethylarsonium iodide.; Finally, in Chapter 6 it was demonstrated that methylarsonic acid (MAsA) is a likely precursor to AsB in the marine environment. Mytilus californianus exposed for 9 days to a seawater system containing (3H) -methylarsonic acid, was found to contain (3H) -methylarsonic acid along with {dollar}lbracksp3{lcub}rm H{rcub}rbrack{dollar}-arsenobetaine and two unknown {dollar}sp3{dollar}H-labeled compounds in the tissue parts of this mussel. (Abstract shortened by UMI.)... |
