Naomi L Stock

Trent University, Питерборо, Ontario, Canada

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Publications (11)33.76 Total impact

  • Naomi L. Stock, Raymond E. March
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    ABSTRACT: Electrospray ionization-mass spectrometry (ESI-MS) is a powerful technique for the detection, identification, and quantification of organic compounds. As mass spectrometers have become more user-friendly and affordable, many students-often with little experience in mass spectrometry-find themselves needing to incorporate mass spectrometry into their research. Herein, a hands-on laboratory experiment for upper-level undergraduate and graduate students to investigate ESI-MS is described. This experiment provides students with the opportunity to observe and use instrumentation discussed in class, to investigate various modes of operation, to compare triple-stage quadrupole (TSQ) with quadrupole linear ion trap (QLIT) instrumentation, and to decide upon the optimum approach for incorporation of mass spectrometry into their research.
    Journal of chemical education 08/2014; 91(8):1244-1247. DOI:10.1021/ed500062w · 1.00 Impact Factor
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    ABSTRACT: Serum albumin binds reversibly with and transports endogenous and exogenous ligands, such as pharmaceuticals, whose therapeutic efficacy is activated upon liberation from the protein. Aqueous perfluoroctanesulfonic acid is a bioaccumulative, pervasive species of anthropogenic origin found in the serum of 90% of Americans that adventitiously binds with high affinity to serum albumin in the same specific site as ibuprofen; thus the conditions for competitive binding are established. This study investigated the competitive interaction between aqueous perfluoroctanesulfonic acid and ibuprofen in binding to bovine serum albumin (BSA) using electrospray ionization mass spectrometry. Perfluoroctanesulfonate was found to displace all bound ibuprofen from BSA and to prevent further ibuprofen binding when the fluorinated analyte concentration exceeds half that of ibuprofen. These observations imply that perfluoroctanesulfonate may displace ibuprofen and similar pharmaceuticals from serum albumin in the body under physiological conditions thus altering the pharmacokinetics and deposition of such drugs.
    International Journal of Mass Spectrometry 07/2013; s 345–347:28–36. DOI:10.1016/j.ijms.2012.12.012 · 2.23 Impact Factor
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    ABSTRACT: Perfluorocarboxylic acids (PFCAs) of chain length greater than seven carbon atoms bioconcentrate in the livers of fish. However, a mechanistic cause for the empirically observed increase in the bioconcentration potential of PFCAs as a function of chain length has yet to be determined. To this end, recombinant rat liver fatty acid-binding protein (L-FABP) was purified, and its interaction with PFCAs was characterized in an aqueous system at pH 7.4. Relative binding affinities of L-FABP with PFCAs of carbon chain lengths of five to nine were established fluorimetrically. The energetics, mechanism, and stoichiometry of the interaction of perfluorooctanoic acid (PFOA) with L-FABP were examined further by isothermal titration calorimetry (ITC) and electrospray ionization combined with tandem mass spectrometry (ESI-MS/MS). Perfluorooctanoic acid was shown to bind to L-FABP with an affinity approximately an order of magnitude less than the natural ligand, oleic acid, and to have at least 3:1 PFOA:L-FABP stoichiometry. Two distinct modes of PFOA binding to L-FABP were observed by ESI-MS/MS analysis; in both cases, PFOA binds solely as the neutral species under typical physiological pH and aqueous concentrations of the anion. A comparison of their chemical and physical properties with other well-studied biologically relevant chemicals showed that accumulation of PFCAs in proteins as the neutral species is predictable. For example, the interaction of PFOA with L-FABP is almost identical to that of the acidic ionizing drugs ketolac, ibuprofen, and warfarin that show specificity to protein partitioning with a magnitude that is proportional to the K(OW) (octanol-water partitioning) of the neutral species. The experimental results suggest that routine pharmacochemical models may be applicable to predicting the protein-based bioaccumulation of long-chain PFCAs.
    Environmental Toxicology and Chemistry 01/2010; 29(8):1669-77. DOI:10.1002/etc.199 · 2.83 Impact Factor
  • Naomi L. Stock, Derek C. G. Muir, Scott Mabury
    Persistent Organic Pollutants, 12/2009: pages 25 - 69; , ISBN: 9780470684122
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    ABSTRACT: Perfluorosulfonates (PFSAs) and perfluorocarboxylates (PFCAs) have been hypothesized to reach remote locations such as the Canadian Arctic either indirectly as volatile precursor chemicals that undergo atmospheric transport and subsequent degradation, or directly via oceanic and atmospheric transport of the PFSAs and PFCAs themselves. Water, sediment, and air samples were collected from three Arctic lakes (Amituk, Char, and Resolute) on Cornwallis Island, Nunavut, Canada. Samples were analyzed for PFSAs and PFCAs, precursor chemicals including the fluorotelomer alcohols (FTOHs) and polyfluorinated sulfonamides (FSAs), and precursor degradation products such as the fluorotelomer unsaturated carboxylates (FTUCAs). PFSAs and PFCAs were detected in water and sediment of all three Arctic lakes (concentrations ranged from nondetect to 69 ng/L and nondetect to 85 ng/g dry weight, respectively). FTOHs and FSAs were observed in air samples (mean concentrations ranged from 2.8 to 29 pg/m3), and confirm that volatile precursors are reaching Arctic latitudes. The observation of degradation products, including FTUCAs observed in sediment and atmospheric particles, and N-ethyl perfluorooctanesulfonamide (NEtFOSA) and perfluorooctanesulfonamide (PFOSA) in air samples, indicate that degradation of the FTOHs and FSAs is occurring in the Arctic environment. PFSAs and PFCAs were also observed on atmospheric particles (mean concentrations ranged from < 0.1 to 5.9 pg/m3). In addition, results of this study also indicate that local perfluoroalkyl contamination of Resolute Lake, which is located downstream of an airport wastewater input, has occurred.
    Environmental Science and Technology 06/2007; 41(10):3529-36. DOI:10.1021/es062709x · 5.48 Impact Factor
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    ABSTRACT: Individual whole body homogenates of 4 year old lake trout (Salvelinus namaycush) samples collected in 2001 from each of the Great Lakes were extracted using a novel fluorophilicity cleanup step and analyzed for perfluoroalkyl compounds (PFCs). Standard addition and internal standardization were used for quantification. Results were reported (+/- SE) for perfluorinated carboxylates (PFCAs), perfluorinated sulfonates (PFSAs), and unsaturated fluorotelomer carboxylates (8:2 and 10:2 FTUCA). The lowest average concentration of sigmaPFC was found in samples from Lake Superior (13+/-1 ng g(-1)), while the highest average concentration was found in samples from Lake Erie (152+/-14 ng g(-1)). Samples from Lake Ontario (60+/-5 ng g(-1)) and Lake Huron (58 +/-10 ng g(-1)) showed similar average sigmaPFC concentrations, although the perfluorinated sulfonate/carboxylate ratios were different. The major perfluoroalkyl contaminant observed was perfluorooctane sulfonate (PFOS) with the highest concentration found in samples from Lake Erie (121+/-14 ng g(-1)), followed by samples from Lake Ontario (46+/-5 ng g(-1)), Lake Huron (39 +/-10 ng g(-1)), Lake Michigan (16+/-3 ng g(-1)), and Lake Superior (5+/-1 ng g(-1)). Perfluorodecane sulfonate (PFDS) was detected in 89% of the samples, with the highest concentration in Lake Erie samples (9.8+/-1.6 ng g(-1)), and lowest concentration in samples from Lake Superior (0.7 +/- 0.1 ng g(-1)). Statistically significant correlations were observed between PFOS and PFDS concentrations, and PFOS concentration and body weight, respectively. The PFCAs were detected in all samples, with the highest total average concentration in samples from Lake Erie (19 ng g(-1)), followed by samples from Lake Huron (16 ng g(-1)), Lake Ontario (10 ng g(-1)), Lake Michigan (9 ng g(-1)) and Lake Superior (7 ng g(-1)). The compounds with significant contributions to the sigmaPFCA concentrations were PFOA and C9-C13-PFCAs. The 8:2 FTUCA was detected at concentrations ranging between 0.1 and 0.2 ng g-1, with the highest level in samples showing also elevated concentrations of PFOA (4.4 ng g(-1) for Lake Michigan vs 1.5 ng g(-1) for all other samples). The 10:2 FTUCA was detected only in 9% of all samples (nd, 45 pg g(-1)). For those PFCs where we determined lake water concentrations, the highest log BAFs were calculated for PFOS (4.1), PFDA (3.9), and PFOSA (3.8).
    Environmental Science and Technology 03/2007; 41(5):1554-9. DOI:10.1021/es0620484 · 5.48 Impact Factor
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    ABSTRACT: Perfluorinated surfactants, including perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA), are an emerging class of environmental contaminants that have recently received considerable attention. An undergraduate laboratory experiment to measure perfluorinated surfactants in fish liver has been developed. Fish samples, collected by students from local markets and grocery stores, are extracted using an ion-pairing method and analyzed using liquid chromatography–tandem mass spectrometry (LC–MS/MS) employing student optimized instrumental parameters. In nearly all fish liver samples analyzed by students, perfluorinated surfactants were detected. This undergraduate experiment provides a hands-on opportunity for students to learn new sample preparation and extraction procedures and the specific techniques of LC–MS/MS. Students gain an appreciation of both the sensitivity of LC–MS/MS for the analysis of trace environmental contaminants and the importance of quality control when working with trace analytes in complex biological matrices. Keywords (Audience): Second-Year Undergraduate
    Journal of chemical education 01/2007; 84(2). DOI:10.1021/ed084p310 · 1.00 Impact Factor
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    ABSTRACT: The UV and IR spectra of CF3CH2CH2OH and F(CF2CF2)xCH2CH2OH (x = 2, 3, 4) were investigated using computational and experimental techniques. Computational methods were used to show that CF3CH2CH2OH and F(CF2CF2)xCH2CH2OH (x = 2, 3) have UV absorption in the region 140–175 nm. Photolysis is therefore not a significant environmental loss mechanism for fluorinated alcohols. Experimental methods were used to record IR spectra for CF3CH2CH2OH and F(CF2CF2)xCH2CH2OH (x = 2, 3, 4) at spectral resolutions of 0.004–0.5 cm−1 with, and without, 700 Torr of air diluent. There was no discernable effect of total pressure or spectral resolution over the range studied. Calculated IR spectra agreed well with those measured experimentally, and were used to assign the IR spectra.
    Journal of Fluorine Chemistry 10/2005; 126:1288-1296. DOI:10.1016/j.jfluchem.2005.06.010 · 1.95 Impact Factor
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    ABSTRACT: Two perfluorinated surfactants, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), were evaluated for their toxicity to the aquatic midge, Chironomus tentans. Impetus for this laboratory study originated from a 10-d, in situ field assessment in which C. tentans was exposed to PFOS at concentrations ranging from 300 to 30,000 microg/L. No midges survived these exposures. Midge survival in a preliminary, acute 10-d laboratory test with nominal PFOS concentrations ranging from 0.1 to 100,000 microg/L showed similar toxicity with respect to survival (median lethal concentration [LC50], 45.2 microg/L) and growth (median effective concentration [EC50], 27.4 microg/L). A parallel test using PFOA indicated no significant impacts on survival or growth. A definitive 10-d assay with PFOS concentrations ranging from 1 to 150 microg/L produced an EC50 for growth (87.2+/-11.6 microg/L) of the same order of magnitude as that in the preliminary findings. The same was not true for survival, however, with the LC50 falling outside the range of test concentrations. To further investigate the sensitivity of C. tentans to PFOS, we conducted a chronic life-cycle test using a nominal concentration range of 1 to 100 microg/L. Three of the four endpoints measured-survival, growth, and emergence-were significantly affected, with EC50 values of 92.2+/-3.1, 93.8+/-2.6, and 94.5+/-3.2 microg/L, respectively. Reproduction was not affected by those PFOS concentrations at which females emerged. The results of the present study indicate that PFOS toxicity thresholds for C. tentans are as much as three orders of magnitude lower than those reported for other aquatic organisms but, at present, are approximately two orders of magnitude higher than those concentrations typically observed in aquatic environments.
    Environmental Toxicology and Chemistry 10/2004; 23(9):2116-23. DOI:10.1897/03-449 · 2.83 Impact Factor
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    ABSTRACT: The influence of the unique, physical properties of poly- and perfluorinated chemicals on vapor pressure was investigated. Vapor pressures of a suite of fluorinated telomer alcohols (FTOHs) (CF3(CF2)nCH2CH2OH, where n = 3, 5, 7, or 9) were measured using the boiling point method and ranged from 144 to 992 Pa. Comparison of experimental and literature values indicate that perfluorocarbons (CF3(CF2)nCF3, where n = 0-6) and fluorinated telomer alcohols have vapor pressures equal to or greater than that of their hydrogen analogues. These chemically counterintuitive results can be explained by the unique geometry of poly- and perfluorinated chemicals--in particular the stiff, helical perfluorinated chain and the significant intramolecular hydrogen bonding of the FTOHs. The majority of models investigated for the estimation of vapor pressure did not compensate for this unique geometry and consistently underpredicted the vapor pressures of the FTOHs. Calculation of partitioning constants using both experimental and estimated vapor pressures indicate that both the Antoine and Modified Grain models, and to a lesser degree the Mackay model, are insufficiently accurate for estimating the vapor pressures of the FTOHs, particularly the longer chain FTOHs. Future models should consider parameters such as geometry, strength, and location of intramolecular hydrogen bonds and otherfunction groups in the molecule in order to improve vapor pressure estimation accuracy. It appears likely that the unique molecular geometry of the FTOHs influences not only their vapor pressure but also other physical properties and hence environmental fate and dissemination.
    Environmental Science and Technology 04/2004; 38(6):1693-9. DOI:10.1021/es034773+ · 5.48 Impact Factor
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    ABSTRACT: In 2001, a sampling campaign was conducted in six North American cities--Reno, NV; Griffin, GA; Cleves, OH; Winnipeg, MB; Long Point, ON; and Toronto, ON--to investigate the tropospheric distribution of a suite of polyfluorinated alcohols and amides. Analysis via gas chromatography-chemical ionization-mass spectrometry indicated that both polyfluorinated sulfonamides and fluorinated telomer alcohols (FTOHs) are widely distributed throughout the North American troposphere with mean concentrations ranging from 22 to 403 pg/m3 and from 11 to 165 pg/m3 respectively. The dominant polyfluorinated contaminant was dependent on sampling location. Large mean concentrations of N-methyl perfluorooctane sulfonamidoethanol (359 pg/m3) and N-ethyl perfluorooctane sulfonamidoethanol (199 pg/m3) identified in Griffin and Reno, respectively, may indicate the release of polyfluorinated sulfonamides to the environment through paper and carpet treatment processes. The nonuniform nature of the spatial distribution of both polyfluorinated sulfonamides and FTOHs is indicative of the importance of point sources for the dissemination of these contaminants in the North American troposphere.
    Environmental Science and Technology 03/2004; 38(4):991-6. DOI:10.1021/es034644t · 5.48 Impact Factor

Publication Stats

455 Citations
33.76 Total Impact Points


  • 2009–2014
    • Trent University
      • • Water Quality Centre
      • • Department of Chemistry
      Питерборо, Ontario, Canada
  • 2004–2007
    • University of Toronto
      • Department of Chemistry
      Toronto, Ontario, Canada