Jody A. Shoemaker

LC/MS/MS structure elucidation of reaction intermediates formed during the TiO2 photocatalysis of microcystin-LR

Microcystin-LR (MC-LR), a cyanotoxin and emerging drinking water contaminant, was treated with TiO(2) photocatalysts immobilized on stainless steel plates as an alternative to nanoparticles in slurry. The reaction intermediates of MC-LR were identified with mass spectrometry (MS) at pH of Milli-Q water (pH(sq)=5.7). Eleven new [M+H](+) were observed in the liquid chromatography mass spectrometry (LC/MS) chromatogram with some of them giving multiple peaks. Most of these reaction intermediates have not been reported from previous studies employing TiO(2) nanoparticles at acidic conditions (pH=4.0). Investigating the effects of pH (for 3.0<pH<7.0), toxin adsorption and initial toxin concentration on the degradation efficiency of the TiO(2) photocatalytic films showed that acidic conditions are preferable for the degradation. Combined with the limited surface area of the films and the absence of additional oxidants (i.e., H(2)O(2)) the degradation was slower and more intermediate steps were identified. Possible structures of the intermediates (formed at neutral pH) after analyzing the corresponding MS/MS spectra are reported. The collision-induced dissociation of the [M+H](+) of MC-LR and the intermediates 1011.5 and 1029.5 are discussed and possible fragmentation pathways and mechanisms are also proposed. Analysis of the MS/MS spectra indicates that the fragmentation of some amino acids is less favorable because of internal interaction with free groups of adjacent amino acids. The MS/MS spectra assisted in determining hydroxylation sites, by the formation or alteration of specific product ions such as m/z 599.

Extraction and detection of a new arsine sulfide containing arsenosugar in molluscs by IC-ICP-MS and IC-ESI-MS/MS

Using IC-ICP-MS and IC-ESI-MS/MS, an unknown arsenical compound in molluscs has been identified as a new arsine sulfide containing analog of a known arsenosugar and is referred to as As(498). This species has been observed in four separate shellfish species following a mild methanol–water extraction. As(498) is unstable, especially in acid, and converts to the arsine oxide containing arsenosugar As(482) over time. Chromatographic retention of As(498) was observed on an anion exchanger ION-120 column but the species did not elute as a well defined peak from a PRP-X100. Mass spectrometric analysis of As(498) at pH 9.0 produced an [M–H]− species at a mass to charge of 497 in the negative-ion mode. A synthetic standard of As(498) was made by bubbling hydrogen sulfide into a stock solution of arsenosugar As(482). The retention time and ESI-MS/MS data were identical for the synthetic standard of As(498) and the unknown arsenical in shellfish extracts.

Analytical methods for water disinfection byproducts in foods and beverages.

The determination of exposure to drinking water disinfection byproducts (DBPs) requires an understanding of how drinking water comes into contact with human through multiple pathways. In order to facilitate the investigation of human exposure to DBPs via foods and beverages, analytical method development efforts were initiated for haloacetonitriles, haloketones, chloropicrin, and the haloacetic acids (HAAs) in these matrices. The recoveries of the target analytes were investigated from composite foods and beverages. Individual foods and beverages used to investigate the general applicability of the developed methods were selected for testing based on their water content and frequency of consumption. The haloacetonitriles, the haloketones, and chloral hydrate were generally well recovered (70–130%), except for bromochloroacetonitrile (64%) and dibromoacetonitrile (55%), from foods spiked after homogenization and following extraction with methyl-t-butyl ether (MTBE); the addition of acetone was found to be necessary to improve recoveries from beverages. The process of homogenization resulted in decreased recoveries for the more volatile analytes despite the presence of dry ice. The HAAs were generally well recovered (70–130%), except for trichloroacetic acid (58%) and tribromoacetic acid (132%), from foods but low recoveries and emulsion formation were experienced with some beverages. With both groups of analytes, certain matrices were more problematic (as measured by volatility losses, emulsion formation) than others with regard to processing and analyte recovery.

An Improved Method for the Analysis of Cryptosporidium parvum Oocysts by Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry

ABSTRACT. Cryptosporidium parvum oocysts were analyzed using matrix‐assisted laser desorption/ionization–time of flight mass spectrometry (MALDI–TOF MS). Sample preparation proved to be a crucial step in the acquisition of acceptable mass spectra. Oocysts of C. parvum and the matrix were mixed and held for at least 45 min to produce reproducible, representative mass spectra. Sporozoites were also excysted from oocysts, purified, and analyzed using MALDI–TOF MS. The mass spectra of the intact oocysts contained many of the same peaks found in the mass spectra of the sporozoites, suggesting that during analysis, the internal constituents, not just the oocyst wall, are ablated by the laser.

Development and multi-laboratory verification of U.S. EPA method 538 for the analysis of drinking water contaminants by direct aqueous injection-LC/MS/MS

A drinking water method for 11 chemicals, predominantly pesticides, is presented that addresses the occurrence monitoring needs of the U.S. Environmental Protection Agency (EPA) for a future Unregulated Contaminant Monitoring Regulation (UCMR). The method employs direct aqueous injection liquid chromatography/tandem mass spectrometry (DAI-LC/MS/MS). The method uses sodium omadine and ammonium acetate to preserve the drinking water samples for up to 14 days. Mean recoveries of tap water samples fortified with the method analytes at 0.99–4.0 μg L−1 (quinoline = 43 μg L−1) are 89.3–106% with relative standard deviations of less than 8%. Single laboratory lowest concentration minimum reporting levels of 0.011–1.5 μg L−1 are demonstrated with this methodology. Multi-laboratory data are presented that demonstrate method ruggedness and transferability. The final method meets all of the EPA UCMR survey requirements for sample collection and storage, precision, accuracy, and sensitivity. The final method is expected to be proposed for use under a future UCMR.

Evaluation of solid phase microextraction for the analysis of hydrophilic compounds.

Two commercially available solid phase microextraction (SPME) fibers, polyacrylate and carboxen/polydimethylsiloxane (PDMS), were evaluated for their ability to extract hydrophilic compounds from drinking water. Conditions, such as desorption time, desorption temperature, sample temperature, sample stirring, methanol concentration in the sample, and ionic strength of the sample, were optimized for 12 hydrophilic compounds (e.g., amines and alcohols) with both fibers. Accuracy, precision, and method detection limits (MDLs) were determined for the target analytes with both fibers. In general, both fibers exhibited excellent accuracy and precision in the range of 91–110% and 1.0–13%, respectively. The carboxen/PDMS fiber extracted these hydrophilic compounds from water with 10 to 100 times lower MDLs (0.10 to 15 μg/l) than the polyacrylate fiber (1.5 to 80 μg/l). The MDLs of the carboxen/PDMS fiber demonstrate that SPME is a feasible approach for extracting hydrophilic compounds from drinking water.

Human Serum IgE Reacts with a Metarhizium anisopliae Fungal Catalase

Background: Previous studies have demonstrated that Metarhizium anisopliae extract can induce responses characteristic of human allergic asthma in a mouse model. The study objectives were (1) to identify and characterize the M. anisopliae mycelia extract (MYC) proteins that are recognized by mouse serum IgE, (2) to determine if human serum IgE reacts with these proteins, and (3) to determine if these IgE-reactive proteins are found in other fungi. Methods: Asthmatic human serum IgE, M. anisopliae crude antigen (MACA) immunized mouse serum IgE, and anti-catalase antibodies were used to probe one- and two-dimensional gel electrophoresis blots of MYC. Results: Mass spectrometry analysis identified catalase as a mouse IgE-reactive protein. This identification was confirmed by assaying catalase activity in the extract and extract immunoblots probed with anti-catalase antibody. Six adult asthmatic sera contained IgE, but not IgG, that was reactive with mycelia extract proteins. A similar protein profile was seen when blots were probed with either mouse anti-MACA IgE or anti-bovine liver catalase antibodies. Furthermore, these mouse anti-MACA and anti-catalase antibodies were cross-reactive with other mold extracts (skin prick testing mix) and Aspergillus niger catalase. Conclusions: Some human asthmatics have developed IgE that reacts with an M. anisopliae catalase, most likely due to cross-reactivity (minimal IgG development). The cross-reactivity among fungal catalases suggests that IgE-reactive catalase might be useful for exposure assessment. Additionally, the similarity of protein profiles visualized with both human and mouse serum IgE suggests that allergy hazard identification can be facilitated using a mouse model.

Development and multi-laboratory verification of U.S. EPA method 540 for the analysis of drinking water contaminants by solid phase extraction-LC/MS/MS

A drinking water method for seven pesticides and pesticide degradates is presented that addresses the occurrence monitoring needs of the US Environmental Protection Agency (EPA) for a future Unregulated Contaminant Monitoring Regulation (UCMR). The method employs online solid phase extraction-liquid chromatography-tandem mass spectrometry (SPE-LC-MS-MS). Online SPE-LC-MS-MS has the potential to offer cost-effective, faster, more sensitive and more rugged methods than the traditional offline SPE approach due to complete automation of the SPE process, as well as seamless integration with the LC-MS-MS system. The method uses 2-chloroacetamide, ascorbic acid and Trizma to preserve the drinking water samples for up to 28 days. The mean recoveries in drinking water (from a surface water source) fortified with method analytes are 87.1-112% with relative standard deviations of <14%. Single laboratory lowest concentration minimum reporting levels of 0.27-1.7 ng/L are demonstrated with this methodology. Multi-laboratory data are presented that demonstrate method ruggedness and transferability. The final method meets all of the EPAs UCMR survey requirements for sample collection and storage, precision, accuracy, and sensitivity.