Effect of Oxygen Concentration on the Detection of Mercury  in an Atmospheric Microwave Discharge

Hadidi, K.; Woskov, P.; Flores, Guadalupe; Green, Kareen; Thomas, Paul D.

doi:10.1143/jjap.38.4595

Cited by 19 publications

(18 citation statements)

References 12 publications

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“…The experimental setup, as described previously 8 was adapted for UV emission/absorption measurements as shown in Figure 1. A 1.5 kW, 2.45 GHz magnetron source irradiated a gas flow in a dielectric tube (25.4 mm i.d.)…”

Section: Methodsmentioning

confidence: 99%

“…It was assumed that the clean water background was representative of the dilute water/HNO 3 acid background spectrum. The aerosol injection, calibration system, and the calculation method for the metals concentration in the gas flow were described previously 8 .…”

Section: Methodsmentioning

confidence: 99%

“…Good detection limits have also been achieved for Cd, Hg, and As in pure nitrogen gas plasmas. However, the detection limit for Hg, Cd, and As has been found to degrade significantly in an air plasma 8 . It is important to understand the mechanisms by which the sensitivity for these metals is degraded in order to be able to further optimize this CEM for its intended application.…”

Section: Introductionmentioning

confidence: 99%

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Observation of self absorption of mercury I and cadmium I emission in an atmospheric microwave sustained plasma

Hadidi

Woskov

Green

et al. 2000

J. Anal. At. Spectrom.

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SummaryAtomic emission spectroscopy of a continuous, atmospheric-pressure microwave sustained plasma in an undiluted slip stream of stack exhaust is under development for real-time monitoring of EPA regulated hazardous metals (As, Be, Cd, Cr, Hg, and Pb). The detection limit in such a plasma for two of these metals on their strongest transitions, Cd I 228.8 nm and Hg I 253.65 nm, has been found to depend on the path length between the plasma and the detection system. Measurements were carried out on long plasma columns >100 mm x ~10 mm diameter sustained in air by approximately 1.5 kW power at 2.45 GHz. The detection limit using a long path-length axial view for UV light collection versus short path-length side views at different points along the plasma column have shown a clear diminution of the signal for the axial view. Self-absorption by unexcited atomic cadmium and mercury is shown to be responsible for diminution of the axial signal. The Cd I 228.8 nm transition was observed to reverse from an emission feature to an absorption feature when the axial path-length was increased.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Observation of self absorption of mercury I and cadmium I emission in an atmospheric microwave sustained plasma

Hadidi

Woskov

Green

et al. 2000

J. Anal. At. Spectrom.

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“…The detection limit for these metals is much lower in pure nitrogen plasmas, but the addition of a small amount of oxygen degrades performance by decreasing the excitation temperature [13]. In the case of arsenic, absorption of the short wavelength UV emission, by oxygen and related species, is the main cause of the high detection limit.…”

Section: Detection Limitsmentioning

confidence: 99%

“…The calibration can change due to changing exhaust chemistry, variable particle loading, deposition of films on windows, temperature drifts of electronics, drifts in optics alignment, and other variables in the field environment of a stack exhaust. Also some metals such as mercury and arsenic have higher detection limits in a stack exhaust plasma due to reduced atomic excitation efficiency [13], increased self absorption, and/or UV absorption by other species such as oxygen and related molecules.…”

Section: Introductionmentioning

confidence: 99%

Accurate and sensitive metals emissions monitoring with an atmospheric microwave-plasma having a real-time span calibration

et al. 2000

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Both high sensitivity and good measurement accuracy are required in a metals continuous emissions monitor in order for it to be acceptable for compliance monitoring. An atmospheric plasma sustained by microwaves with an attached source of a calibrated trace metals aerosol has been shown to be capable of achieving both of these requirements. The microwave plasma is continuous and operates in undiluted stack exhaust for atomic emission spectroscopy of trace metals. The plasma is sustained in a shorted waveguide that is attached to the stack by a short sample line (< 50 cm). It is powered at 1.5 kW, at a frequency of 2.45 GHz. An undiluted stack slipstream is isokinetically drawn into the plasma by a suction pump at a nominal flow of 14 liters per minute. The pneumatic nebulizer attached to the sample line can momentarily, on command, inject a known concentration of metals solution providing a real-time span calibration. The system was tested on the exhaust stack of the rotary kiln incinerator simulator facility at the Environmental Protection Agency (EPA) National Risk Management Laboratory in Research Triangle Park. Three hazardous metals were monitored, lead, chromium, and beryllium. These measurements were referenced to EPA Method-29. A total of twenty spiked stack exhaust tests were carried out. Ten one-hour tests at high concentration (40-60 µg/actual m 3 ) and ten one and half-hour tests at low concentration (10-15 µg/actual m 3 ). The microwave plasma monitor achieved relative accuracies of approximately 20% for lead and beryllium and 40% for chromium with a threshold detection capability of < 3 µg/actual m 3 for a time response of ∼1-minute. The relative accuracy deviation from the EPA Method-29 was found to be mostly systematic. This suggests the possibility of using a site-specific calibration to bring the microwave plasma into compliance with EPA's goal of 20% relative accuracy to the reference method. Laboratory work is continuing to add mercury, arsenic, and cadmium to the monitored metals. Mercury and arsenic present a particular challenge to achieving high detection sensitivity in undiluted stack exhaust because the plasma is less efficient in exciting Hg and because UV absorption interferes with As detection. This is a problem that is also in common with air ICP and in situ spark plasma methods for continuous emissions monitoring of metals. INTRODUCTIONAdvancing the state-of-the-art of continuous emissions monitoring (CEM) technology for rapid and simultaneous detection of all hazardous metals in stack exhaust is currently the focus of significant development activity. Such a CEM must be able to monitor at a minimum six of the Resource Conservation and Recovery Act (RCRA) metals: arsenic, beryllium, cadmium, chromium, lead, and mercury. Detection limits on the order of 1µg/m 3 are needed with minimum accuracies of 20% relative to the current Environmental Protection Agency (EPA) reference method. In addition, the goal is to develop an instrument that is affordable, easy to use, low maintena...

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Microwave Plasma Systems in Optical and Mass Spectroscopy

Jankowski

Reszke²,

Broekaert

et al. 2011

Encyclopedia of Analytical Chemistry

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The art and science of microwave plasma (MWP) optical and mass spectroscopy is briefly presented including very recent advances in the field up to 2011. The use of MWPs as radiation sources for optical emission spectroscopy (OES) and atomic fluorescence spectroscopy (AFS) and as atom reservoirs for atomic absorption spectroscopy (AAS), cavity ringdown spectroscopy (CRDS), and laser‐enhanced ionization spectroscopy (LEIS) as well as ion sources for mass spectrometry (MS) is treated. Devices for producing both E‐type capacitively coupled microwave plasma (CMP)‐electrode and microwave‐induced plasma (MIP)‐electrodeless MWPs, including inductively coupled plasma (ICP)‐like H‐type plasmas, are classified and discussed, in addition to methods of their diagnostics, and results for the analytically relevant plasma parameters are presented. The means of generation of symmetrical plasmas and uses of microplasma devices are also presented with an effort to comment on general classification of microwave (MW) cavities. Further, the use of MWs for boosting of glow discharges (GDs) is treated along with other tandem sources. Methods for the introduction of gaseous, liquid, and solid samples into the MWP are discussed. They include direct vapor sampling (DVS), chemical vapor generation (CVG), and hydride generation (HG) techniques; dry aerosol generation techniques (electrothermal vaporization (ETV); spark ablation (SA); laser ablation (LA); and continuous powder introduction (CPI) as well as wet aerosol generation techniques using both solution and slurry nebulization. Special reference is made to coupling with gas chromatography (GC) and also with various separation techniques for liquids including high‐performance liquid chromatography (HPLC). The analytical figures of merit in the case of OES with low‐power and high‐power MIP, CMP, microwave plasma torch (MPT), MWP‐electrode sources including rotating field sustained plasma and H‐type MWP as well as microplasmas are given. There are also described cases of atomic absorption, fluorescence, and laser ionization with these sources. The developments in MS in the case of both low‐power and high‐power MWPs and in the case of various types of sample introduction techniques are discussed. Applications of MWP analytical spectroscopy are in the fields of biological samples with special reference to microanalysis, and of environmental and industrial samples with special emphasis on element speciation, on‐line monitoring, particle sizing, and direct solids analysis. A critical comparison of the methodology with other spectroscopic methods for the determination of the elements and their species is given.

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Effect of Oxygen Concentration on the Detection of Mercury in an Atmospheric Microwave Discharge

Cited by 19 publications

References 12 publications

Observation of self absorption of mercury I and cadmium I emission in an atmospheric microwave sustained plasma

Observation of self absorption of mercury I and cadmium I emission in an atmospheric microwave sustained plasma

Accurate and sensitive metals emissions monitoring with an atmospheric microwave-plasma having a real-time span calibration

Microwave Plasma Systems in Optical and Mass Spectroscopy

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