Traceability of the output concentration of mercury vapor generators

Long, Stephen E.; Norris, James E; Carney, Jennifer; Ryan, Jeffrey V.; Mitchell, Gerald D.; Dorko, William D.

doi:10.1016/j.apr.2019.12.012

Cited by 6 publications

(10 citation statements)

References 3 publications

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“…The mass of collected Hg is subsequently analyzed using ID-CV-ICP-MS. Below, we describe key features of the overall sampling method, noting that the underlying principles and methodologies of Hg 0 generator, sorbent trap, ID-CV-ICP-MS, and LAS have been published earlier. [12][13][14]17 The notations Hg and MS represent the Hg 0 state and ID-CV-ICP-MS, respectively, when not explicitly indicated.…”

Section: Methodsmentioning

confidence: 99%

“…The volumetric flow rate of the gas passing through the sorbent tube is measured using a calibrated laminar flow element (LFE) flowmeter, and this quantity is integrated over the collection time to provide the total volume of carrier gas associated with the mercury that is collected by the trap. The mass of collected Hg is subsequently analyzed using ID-CV-ICP-MS. Below, we describe key features of the overall sampling method, noting that the underlying principles and methodologies of Hg 0 generator, sorbent trap, ID-CV-ICP-MS, and LAS have been published earlier. − , The notations Hg and MS represent the Hg 0 state and ID-CV-ICP-MS, respectively, when not explicitly indicated.…”

Section: Methodsmentioning

confidence: 99%

“…We used single-section (6 mm diameter) commercial iodinated acid-washed coconut-shell carbon sorbent traps and followed a mercury capture protocol, consistent with our prior studies. , The trap collection time was varied across the span concentration to ensure constant adsorbate loading. The volumetric flow rate through the trap was controlled and the total flow was recorded (see Supporting Information, Table S1.I) using an LFE that had been calibrated against secondary flow standards at NIST.…”

Section: Methodsmentioning

confidence: 99%

“…These systems, referred to as NIST prime (NP) generators, are traceable to the unit of the International System of Units (SI) through periodic certification against the isotope dilution cold-vapor inductively coupled plasma mass spectrometry (ID-CV-ICP-MS) method. A description of the NP systems and SI traceability rationale can be found in recent publications by Long et al , In brief, the two NPs are labeled NP Low and NP High, together spanning four orders of magnitude in mass concentration and providing coverages of (0.3 to 40) μg/m 3 and (40 to 300) μg/m 3 , respectively. Determination of the output Hg mass concentration provided by each NP generator involves three steps: (1) passive sampling of the flow stream using a carbon sorbent trap, (2) measurements of the loaded mercury using the ID-CV-ICP-MS method which requires spiking by a solution containing 201 Hg 2+ , and (3) measurements of the total gas volume passing through the trap.…”

Section: Introductionmentioning

confidence: 99%

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Comparison of Primary Laser Spectroscopy and Mass Spectrometry Methods for Measuring Mass Concentration of Gaseous Elemental Mercury

et al. 2020

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We present a direct comparison between two independent methods for the measurement of gaseous elemental mercury (GEM) mass concentration: isotope dilution cold-vapor inductively coupled plasma mass spectrometry (ID-CV-ICP-MS) and laser absorption spectroscopy (LAS). The former technique combined with passive sorbent tube sampling is currently the primary method at NIST for mercury gas standards traceability to the International System of Units (SI). This traceability is achieved via measurements on a mercury-containing reference material. The latter technique has been recently developed at NIST and involves real-time measurements of light attenuation caused by GEM, with SI traceability based in part on the known spontaneous emission lifetime of the probed 6 1S0–6 3P1 intercombination transition of elemental mercury (Hg0). Using a steady-flow Hg0-in-air generator to produce samples measured by both methods, we use LAS to measure the sample gas and in parallel we collect the Hg0 on sorbent tubes to be subsequently analyzed using ID-CV-ICP-MS. Over the examined mass concentration range (41 μg/m3 to 287 μg/m3 Hg0 in air), the relative disagreement between the two approaches ranged from (1.0 to 1.8)%. The relative combined standard uncertainty on average is 0.4% and 0.9%, for the LAS and MS methods, respectively. Our comparison studies help validate the accuracy of the ID-CV-ICP-MS primary method as well as establish the LAS technique as an attractive alternative primary method for SI-traceable measurements of GEM.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Comparison of Primary Laser Spectroscopy and Mass Spectrometry Methods for Measuring Mass Concentration of Gaseous Elemental Mercury

et al. 2020

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“…NIST SRM 3133 (Mercury Standard Solution) was used for calibrating the ICP-MS method. Since NIST SRM 3133 is traceable to SI units, an unbroken chain of traceability to SI units was achieved [ 15 ]. Srivastava et al [ 16 ] applied a high-resolution absorption spectroscopy method to achieve SI traceability for the GEM measurement.…”

Section: Introductionmentioning

confidence: 99%

Validating an Evaporative Calibrator for Gaseous Oxidized Mercury

Gacnik

Živković

Guevara

et al. 2021

Sensors

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Understanding atmospheric mercury chemistry is the key for explaining the biogeochemical cycle of mercury and for improving the predictive capability of computational models. Increased efforts are being made to ensure comparable Hg speciation measurements in the air through establishing metrological traceability. While traceability for elemental mercury has been recently set, this is by no means the case for gaseous oxidized mercury (GOM). Since a calibration unit suitable for traceable GOM calibrations based on evaporation of HgCl2 solution was recently developed, the purpose of our work was to extensively evaluate its performance. A highly specific and sensitive 197Hg radiotracer was used for validation over a wide range of concentrations. By comparing experimental and calculated values, we obtained recoveries for the calibration unit. The average recoveries ranged from 88.5% for 1178 ng m−3 HgCl2 gas concentration to 39.4% for 5.90 ng m−3 HgCl2 gas concentration. The losses were due to the adsorption of oxidized Hg on the inner walls of the calibrator and tubing. An adsorption isotherm was applied to estimate adsorption enthalpy (ΔHads); a ΔHads value of −12.33 kJ mol−1 was obtained, suggesting exothermal adsorption. The results of the calibrator performance evaluation suggest that a newly developed calibration unit is only suitable for concentrations of HgCl2 higher than 1 µg m−3. The concentration dependence of recoveries prevents the system from being used for calibration of instruments for ambient GOM measurements. Moreover, the previously assessed uncertainty of this unit at µg m−3 level (2.0%, k = 2) was re-evaluated by including uncertainty related to recovery and was found to be 4.1%, k = 2. Calibrator performance was also evaluated for HgBr2 gas calibration; the recoveries were much lower for HgBr2 gas than for HgCl2 gas even at a high HgBr2 gas concentration (>1 µg m−3). As HgBr2 is often used as a proxy for various atmospheric HgBr species, the suitability of the unit for such calibration must be further developed.

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