S. N. Willie

National Research Council Canada, Ottawa, Ontario, Canada

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Publications (91)223.88 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A measurement model based on the use of a pin-cell glow discharge source coupled to a VG 9000 sector field mass spectrometer (GD-MS) for the assignment of purity of high-purity metals, i.e., mass fraction of metal matrix, w(M), is presented. A mass balance approach to the calculation requires the determination and summation of impurity mass fractions of all extraneous elements present, including non-metals and gases. It is posited that a primary method of measurement can be devised to yield direct traceability of results to the SI. The major source of uncertainty in the traceability chain stems from the need to adjust the initially estimated quantity values of each impurity element by a relative sensitivity factor 'influence quantity' , derived from ab initio calculations, and validated through comparison with those derived through use of Certified Reference Materials. It is argued that the method is sufficiently well understood that a measurement equation can be formulated for which all parameters are measured in terms of SI units; that all contributions to uncertainty of measurement can be quantitatively evaluated, underpinning the metrological traceability; and that the performance of GD-MS in CCQM key and pilot comparisons of trace elements in complex metal matrices is in conformance with claimed capabilities. The applicability of the approach to metals in the 3N to 7N range of purity shows that fit-for-purpose relative expanded uncertainties of 0.5% to 0.000 05% can be conservatively achieved for w(M). Presentation of various instrument calibration scenarios vis-à-vis impact on SI traceability of results is also undertaken with a view to eliciting further discussion of this concept within the metrological community.
    Metrologia 06/2014; 51(5):410. · 1.90 Impact Factor
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    ABSTRACT: The key comparison CCQM-K89 was undertaken to demonstrate the capability of participating NMIs and DIs in measuring the contents of incurred trace elements (total arsenic, cadmium and lead) and essential elements (calcium and zinc) at µg/g (for arsenic, cadmium, lead and zinc) and mg/g (for calcium) levels in a herb matrix sample by various analytical techniques.
    Metrologia 01/2013; 50(1A):08003. · 1.90 Impact Factor
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    ABSTRACT: An accurate and precise method for the determination of arsenobetaine (AsB, (CH(3))(3)(+)AsCH(2)COO(-)) in fish samples using exact matching species specific isotope dilution (ID) liquid chromatography LTQ-Orbitrap mass spectrometry (LC-LTQ-Orbitrap-MS) and standard addition LC inductively coupled plasma mass spectrometry (LC-ICPMS) is described. Samples were extracted by sonication for 30 min with high purity deionized water. An in-house synthesized (13)C enriched AsB spike was used for species specific ID analysis whereas natural abundance AsB, synthesized and characterized by quantitative (1)H NMR (nuclear magnetic resonance spectroscopy), was used for reverse ID and standard addition LC-ICPMS. With the LTQ-Orbitrap-MS instrument in scan mode (m/z 170-190) and resolution set at 7500, the intensities of [M + H](+) ions at m/z of 179.0053 and 180.0087 were used to calculate the 179.0053/180.0087 ion ratio for quantification of AsB in fish tissues. To circumvent potential difficulty in mass bias correction, an exact matching approach was applied. A quantitatively prepared mixture of the natural abundance AsB standard and the enriched spike to give a ratio near one was used for mass bias correction. Concentrations of 9.65 ± 0.24 and 11.39 ± 0.39 mg kg(-1) (expanded uncertainty, k = 2) for AsB in two fish samples of fish1 and fish2, respectively, were obtained by ID LC-LTQ-Orbitrap-MS. These results are in good agreement with those obtained by standard addition LC-ICPMS, 9.56 ± 0.32 and 11.26 ± 0.44 mg kg(-1) (expanded uncertainty, k = 2), respectively. Fish CRM DORM-2 was used for method validation and measured results of 37.9 ± 1.8 and 38.7 ± 0.66 mg kg(-1) (expanded uncertainty, k = 2) for AsB obtained by standard addition LC-ICPMS and ID LC-LTQ-Orbitrap-MS, respectively, are in good agreement with the certified value of 39.0 ± 2.6 mg kg(-1) (expanded uncertainty, k = 2). Detection limits of 0.011 and 0.033 mg kg(-1) for AsB with LC-ICPMS and ID LC-LTQ-Orbitrap-MS, respectively, were obtained demonstrating that the technique is well suited to the determination AsB in fish samples. To the best of our knowledge, this is first application of species specific isotope dilution for the accurate and precise determination of AsB in biological tissues.
    Analytical Chemistry 04/2011; 83(9):3371-8. · 5.82 Impact Factor
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    ABSTRACT: A procedure is detailed for the determination of trace metals in high salinity petroleum produced formation water (PFW) by inductively coupled plasma mass spectrometry (ICP-MS) coupled with flow injection (FI) on-line matrix separation and preconcentration. High salinity PFW waters present complex composition containing various organic and inorganic substances. Mini-columns packed with Toyopearl AF-Chelate-650M iminodiacetate resin were used for the analyte separation/preconcentration of Cd, Pb, Ni, Zn, V, Co and U; Toyopearl 8-hydroxiquinoline resin for Fe, and silica immobilized 8-hydroxyquinoline resin for Mo. A Doehlert matrix and desirability function was used to generate response surfaces to optimize the column separation/preconcentration parameters. Using 7.5 mL aliquots of PFW, method limits of detection of 0.0007, 0.009, 0.017, 0.024, 0.0002, 0.047, 0.058, 0.002, 0.013 and 0.041 ng ml−1 were obtained for Cd, Pb, Ni, Zn, U, Mo, Fe, Co, V and Mn, respectively. Vanadium, Co and Mn were determined by the method of standard additions whereas Cd, Pb, Ni, Zn, Mo, Fe and U were quantitated using isotope dilution. CASS-4 (coastal seawater) certified reference material was used for method validation and high-salinity PFW (39–120‰) from Brazilian offshore platforms examined. The concentration ranges found in these waters were 0.013–1.47, 0.057–0.80, 0.229–5.1, 0.096–3360, 0.001–0.081, 0.244–69, 0.84–1419, 0.004–3.5, 0.088–0.85 and 4.2–6230 ng ml−1 for Cd, Pb, Ni, Zn, U, Mo, Fe, Co, V and Mn, respectively.
    Journal of Analytical Atomic Spectrometry 03/2011; 26(3):578-585. · 3.40 Impact Factor
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    ABSTRACT: An intralaboratory determination of total Sn in three National Research Council of Canada reference materials, i.e., estuarine sediments BCSS-1 and MESS-1 and lobster hepatopancreas TORT-1 was undertaken. Samples were solubilized by acid mineralization and analyzed by stable isotope dilution inductively coupled plasma mass spectrometry, direct solution injection graphite furnace atomic absorption spectrometry (GFAAS), and hydride generation-GFAAS. The materials were homogeneous at the 500 mg subsample size. Good agreement was obtained amongst the results from the three instrumental methods of analysis. Certified values of total Sn in these materials are 1.85 ± 0.20 μg/g in BCSS-1, 3.98 ± 0.44 μg/g in MESS-1, and 139 ± 11 ng/g in TORT-1. The above uncertainties represent 95% tolerance limits for an individual (500 mg) subsample.
    02/2011;
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    ABSTRACT: A method for direct determination of molybdenum in seawater has been developed, and uses linear sweep voltammetry after adsorptive accumulation of the Erichrome Blue Black R (EBBR) complex on a static mercury drop electrode. To an acidified (pH 1.6) seawater (SW) sample, 6.0 × 10−6 M EBBR is added and preconcentration by adsorption is carried out for 30 s at a potential of −0.05 V vs. the Ag/AgCl/SW reference electrode. The potential is then scanned in the negative direction, giving a current peak for the reduction of the Mo—EBBR complex at −0.17 V. Under these conditions the limit of detection is 0.50 ng/mL. Experimental results for Mo in seawater using this technique agree well with certified values for two reference seawater samples (NASS-1, CASS-1).
    02/2011;
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    ABSTRACT: This work explores the performance of laser ablation-inductively coupled plasma mass spectrometry using different types of single-collector devices (sector field and time-of-flight instrumentation) for lead isotopic analysis of bronze coins, minted in the ancient city of Bilbilis. The aim of the study was achieving sufficient discrimination power to reveal similarities and differences for coins originating from different historical periods, and to obtain information on the possible source of the lead ores used in their production, while restricting the damage inflicted to the samples such that it is not visible to the naked eye. It was found that satisfactory results (RSD in the 0.15-0.30% range for (207)Pb/(206)Pb and (208)Pb/(206)Pb ratios) could be finally obtained, despite the noisy nature of signals generated upon ablation of the highly inhomogeneous coins, by means of a methodology based on: (a) selection of the line profiling ablation mode; (b) use of a dual pass spray chamber that permits the simultaneous introduction of a solution (containing thallium of known isotopic composition), thus resulting in a wet plasma that showed an increased robustness towards matrix effects and (c) detection using a TOF-ICPMS unit, which proved to be much better suited to deal with the transient signals obtained, while being also sufficiently sensitive to obtain good counting statistics, owing to the high lead level (average around 5%) present in the samples. Moreover, under these conditions, the simultaneous aspiration of the thallium spike permitted accurate correction for mass discrimination, such that it was not necessary to use external matrix-matched standards for calibration.
    Analytica chimica acta 09/2010; 677(1):55-63. · 4.31 Impact Factor
  • Tomohiro Narukawa, Scott Willie
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    ABSTRACT: Laser ablation of dried deposits of solubilized biological tissues with detection by ICP-TOF-MS was evaluated for trace metal determination. Solubilization was accomplished through simple treatment with formic acid. Aliquots of this solution were dried under a heat lamp, the resulting smooth hard deposit could be easily ablated. The main advantage of the technique is that a uniform solution is produced by the formic acid at which point aqueous internal and calibration standards can be added prior to drying and used for quantitation. This approach addresses the issue of calibration with LA based techniques. Detection limits were 1, 2, 6, 1, 0.2 and 0.05 mg kg−1 for Mn, Cu, Zn, As, Cd, and Pb, respectively. Alternatively, certified reference materials treated in the same manner can also be used for calibration. Linear calibration curves were constructed for the six elements listed using NRCCCRMsTORT-2, DOLT-4, DORM-3 and NIST SRMs 2976, 1566b and RM 8414.
    Journal of Analytical Atomic Spectrometry 01/2010; 25(7). · 3.40 Impact Factor
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    Analytica Chimica Acta 01/2010; 677:55-63. · 4.39 Impact Factor
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    ABSTRACT: Total filterable mercury (TFM) and lead-210 ((210)Pb) were measured for a one-year air particulate sample series collected weekly at Resolute (74.7 degrees N, 95.0 degrees W), a Canadian high Arctic site, during July 1999 and June 2000. The measurements showed a clear time lag of two months between the peak concentrations of TFM and (210)Pb.
    Journal of Environmental Monitoring 09/2009; 11(8):1460-1. · 2.09 Impact Factor
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    ABSTRACT: The long-term (1974-2000) time trend of total filterable mercury (TFM) in the air in the Canadian Arctic is reported. The concentration of TFM had declined by (3.0+/-0.8) % and (3.1+/-0.9) % per year in the summer and fall, respectively, over the 27 years, which coincided with the calculated reduction rate of world-wide mercury emission (~3.3% per year) from human activities between 1983 and 1995. The time trend for winter and early spring was not statistically significant as the variability of TFM was very large, partly due to Arctic Mercury Depletion Events and partly due to Arctic haze.
    Science of The Total Environment 02/2009; 407(8):2756-9. · 3.16 Impact Factor
  • Lu Yang, Scott Willie, Ralph E. Sturgeon
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    ABSTRACT: An on-line matrix separation and concentration was undertaken for the direct determination of total Cr in seawater using isotope dilution with detection by sector field inductively coupled plasma mass spectrometry (ID SF-ICP-MS). A mini-column packed with 50 µl silica-immobilized diphenylcarbazone (I-DPC) resin was used to extract Cr(III) from seawater following on-line pH adjustment with a pH 9.3 solution of NH4OH/HNO3. A preliminary reduction of chromium to Cr(III) was achieved with hydroxylamine hydrochloride. Medium resolution was used to efficiently separate argon polyatomic species and any possible oxide interferences. Using a 7.5 ml volume of sample, throughput was 10 samples h−1 with a detection limit (3 s) of 0.005 ng g−1.
    Journal of Analytical Atomic Spectrometry 01/2009; 24(7). · 3.40 Impact Factor
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    ABSTRACT: A suite of three ginkgo-containing dietary supplement Standard Reference Materials (SRMs) has been issued by the National Institute of Standards and Technology (NIST) with certified values for flavonoid aglycones, ginkgolides, bilobalide, and selected toxic trace elements. The materials represent a range of matrices (i.e., plant, extract, and finished product) that provide different analytical challenges. The constituents have been determined by at least two independent analytical methods with measurements performed by NIST and at least one collaborating laboratory. The methods utilized different extractions, chromatographic separations, modes of detection, and approaches to quantitation. The SRMs are primarily intended for method validation and for use as control materials to support the analysis of dietary supplements and related botanical materials.
    Analytical and Bioanalytical Chemistry 10/2007; 389(1):179-96. · 3.66 Impact Factor
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    ABSTRACT: Cold vapor generation arising from reduction of both Hg(2+) and CH(3)Hg(+) occurs using ultrasonic (US) fields of sufficient density to achieve both localized heating as well as radical-based attack in solutions of formic and acetic acids and tetramethylammonium hydroxide (TMAH). A batch sonoreactor utilizing an ultrasonic probe as an energy source and a flow through system based on a US bath were optimized for this purpose. Reduction of CH(3)Hg(+) to Hg(0) occurs only at relatively high US field density (>10 W cm(-3) of sample solution) and is thus not observed when a conventional US bath is used for cold vapor generation. Speciation of mercury is thus possible by altering the power density during the measurement process. Thermal reduction of Hg(2+) is efficient in formic acid and TMAH at 70 degrees C and occurs in the absence of the US field. Room temperature studies with the batch sonoreactor reveal a slow reduction process, producing temporally broad signals having an efficiency of approximately 68% of that arising from use of a conventional SnCl(2) reduction system. Molecular species of mercury are generated at high concentrations of formic and acetic acid. Factors affecting the generation of Hg(0) were optimized and the batch sonoreactor used for the determination of total mercury in SLRS-4 river water reference material.
    Analytical and Bioanalytical Chemistry 06/2007; 388(4):849-57. · 3.66 Impact Factor
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    ABSTRACT: The determination of Sr in environmental samples by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) is described. Two ETV devices, a commercially available HGA-600MS graphite tube unit and a home-made W-coil, were examined in combination with DRC technology to remove isobaric interferences when measuring 90Sr. Best results were obtained using the HGA-600MS device. Interferences from Y and Zr could be removed when these elements were present at concentrations up to 1 and 100 mg kg−1, respectively, an improvement of 15 and 30-fold over solution nebulization. Temporal separation of analyte and isobaric interferents makes possible the use of simplified sample preparation procedures, substantially increasing sample throughout and reducing the chances of analyte loss or contamination. For the graphite-based HGA system, procedural LODs of 3.5 pg g−1 could be obtained with precision better than 7% at 350 pg g−1. The accuracy of the method was validated by determination of natural Sr in NRC CRM MESS-3 (Marine Sediment), LUTS-1 (Non Defatted Lobster Hepatopancreas), PACS-2 (Marine Sediment) and SLRS-4 (Riverine Water) and by recovery of 90Sr spikes added to these matrices.
    Journal of Analytical Atomic Spectrometry 01/2007; 22(11). · 3.40 Impact Factor
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    ABSTRACT: The performance of solution nebulization (SN), electrothermal vaporization (ETV) and laser ablation (LA) of dried micro-droplets as sample introduction systems for ICP-MS are compared for the determination of several radionuclides in digested biological tissue, nearshore sea-water and river water. Samples were subjected to a Ca3(PO4)2 co-precipitation preconcentration prior to analysis. Each introduction system possesses unique advantages and disadvantages. ETV accommodates samples having higher dissolved solids content; consequently, for SN and LA, sample concentrates require additional dilution by 50- and 10-fold, respectively. ETV and LA achieved similar sensitivities and limits of detection, the latter ranging from 0.017 to 0.029 pg ml−1. Although SN provides the best precision (2% RSD versus 7 and 8% for ETV and LA, respectively), formation of uranium hydride can be reduced at least 100-fold using LA of dried micro-droplets of samples. The accuracy of the method was validated by determination of U and Th in NIST SRM 1566b Oyster Tissue, NRC CRM CASS-4 Nearshore Seawater and SLRS-4 Riverine Water and via spike recoveries for Pu.
    Journal of Analytical Atomic Spectrometry 10/2006; · 3.40 Impact Factor
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    ABSTRACT: A new selenized yeast reference material (SELM-1) produced by the Institute for National Measurement Standards, National Research Council of Canada (INMS, NRC) certified for total selenium (2,059+/-64 mg kg(-1)), methionine (Met, 5,758+/-277 mg kg(-1)) and selenomethionine (SeMet, 3,431+/-157 mg kg(-1)) content is described. The +/-value represents an expanded uncertainty with a coverage factor of 2. SeMet and Met amount contents were established following a methanesulfonic acid digestion of the yeast using GC-MS and LC-MS quantitation. Isotope dilution (ID) calibration was used for both compounds, using 13C-labelled SeMet and Met. Total Se was determined after complete microwave acid digestion based on ID ICP-MS using a 82Se spike or ICP-OES spectrometry using external calibration. An international intercomparison exercise was piloted by NRC to assess the state-of-the-art of measurement of selenomethione in SELM-1. Determination of total Se and methionine was also attempted. Seven laboratories submitted results (2 National Metrology Institutes (NMIs) and 5 university/government laboratories). For SeMet, ten independent mean values were generated. Various acid digestion and enzymatic procedures followed by LC ICP-MS, LC AFS or GC-MS quantitation were used. Four values were based on species-specific ID calibration, one on non-species-specific ID with the remainder using standard addition (SA) or external calibration (EC). For total selenium, laboratories employed various acid digestion procedures followed by ICP-MS, AFS or GC-MS quantitation. Four laboratories employed ID calibration, the remaining used SA or EC. A total of seven independent results were submitted. Results for methionine were reported by only three laboratories, all of which used various acid digestion protocols combined with determination by GC-MS and LC UV. The majority of participants submitted values within the certified range for SeMet and total Se, whereas the intercomparison was judged unsuccessful for Met because only two external laboratories provided values, both of which were outside the certified range.
    Analytical and Bioanalytical Chemistry 06/2006; 385(1):168-80. · 3.66 Impact Factor
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    ABSTRACT: Total mercury in biological samples was determined by flow injection (FI) cold vapour atomic absorption spectrometry (CVAAS) following tissue solubilization with formic acid. A mixture of potassium bromide and potassium bromate was used to decompose organomercury compounds prior to their reduction with sodium borohydride. A gold amalgam system was used to achieve lower detection limits when required. National Research Council Canada certified reference materials dogfish liver (DOLT-3), dogfish flesh (DORM-2) and lobster hepatopancreas (TORT-2), as well as oyster tissue (NIST SRM 1566b) and mussel tissue (NIST SRM 2976) were used to assess the accuracy of the method. The method of standard additions provided the most accurate results. Limit of detection (LOD) for Hg in the solid sample of 0.001 and 0.01mugg(-1) were achieved with and without amalgamation, respectively. The precision of measurement for 1.6ngml(-1) methylmercury was 2.7% using the amalgam system.
    Talanta 03/2006; 68(4):1259-63. · 3.50 Impact Factor
  • R. Sturgeon, S. N. Willie, Z. Mester
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    ABSTRACT: A combined spray chamber/UV photolysis unit is described which is shown to substantially enhance sample introduction efficiency for several elements in the presence of 1–5% concentrations of formic, acetic and propionic acids. Enhancement factors of 2–40-fold were achieved for Ag, As, Se, Sb, Hg, I, Bi, Pb and Sn when the aerosol field within the cyclonic chamber produced during conventional concentric nebulizer sample introduction was illuminated by an axially placed 6 W mercury pen lamp. UV photolysis of the organic acids likely initiates radical reactions, generating volatile analyte species.
    Journal of Analytical Atomic Spectrometry 02/2006; · 3.40 Impact Factor
  • S. N. Willie, Z. Mester, R. Sturgeon
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    ABSTRACT: An assessment of inductively coupled plasma orthogonal acceleration time-of-flight mass spectrometry (ICP-oa-TOF-MS) for measurement of isotope ratios arising from steady-state and transient signal detection is presented. An HPLC pump and autosampler were used to introduce microliter volumes of analyte solution into a carrier flow to generate precise and repeatable transient signals having a FWHM of approximately 1 s. Analog and pseudo pulse data processing modes were evaluated and found to obey Poisson statistics for prediction of isotope ratio performance. Use of pseudo pulse counting is restricted by the limited linear range of response and cannot exceed approximately 0.2 counts per pushout. This limitation does not impede analog detection, which thus permits precise isotope ratio measurements to be achieved at higher analyte concentrations using shorter integration times. For transient signals, area measurements are superior to averaging point-to-point measurements across the peak for optimum ratio precision. Although the TOF system provides for simultaneous sampling of the extracted pulse, thereby permitting elimination of correlated noise through ratioing techniques, detection remains sequential and noise components present in the detection system limit isotope ratio precision in this study to 0.04% RSD.
    Journal of Analytical Atomic Spectrometry 11/2005; · 3.40 Impact Factor

Publication Stats

690 Citations
223.88 Total Impact Points

Institutions

  • 1982–2013
    • National Research Council Canada
      • Institute for National Measurement Standards (INMS)
      Ottawa, Ontario, Canada
  • 2010
    • University of Zaragoza
      • Faculty of Sciences (CIENCIAS)
      Zaragoza, Aragon, Spain
  • 2007
    • Federal University of Santa Catarina
      • Departamento de Química
      Florianópolis, Estado de Santa Catarina, Brazil
  • 2006
    • Hokkaido University of Education
      Sapporo, Hokkaidō, Japan