Helium Microwave-induced Plasma Research Articles

Determination of Fluorine Chemical Structure in Slag by Thermal Hydrolysis He-MIP-OES.

A novel microwave-induced helium plasma optical emission spectrometry (He-MIP-OES) combined with a thermal hydrolysis sample introduction system was newly established for the determination of fluorine (F) compounds in slags. The MIP maintained through an Okamoto cavity was adopted, which was quite stable and provided a higher detection capability of F by helium plasma. The basic analytical performance of He-MIP-OES combined with an ultrasonic nebulizer for F analysis was also examined, and expected results could be obtained. The thermal hydrolysis behavior of CaF2, Ca4(Si2O7)(F,OH)2 and Ca5(PO4)3F, as known F chemical structures in slag, was also examined by thermal hydrolysis He-MIP-OES; F compounds in actual slag could be successfully identified and determined by this developed system.

Direct Measurement of Elemental Mercury Using Multidimensional Gas Chromatography with Microwave-Induced Helium Plasma Atomic Emission Spectroscopy

Microwave-induced helium plasma atomic emission spectroscopy permits direct measurement of picogram levels of elemental mercury in various matrices when combined with multidimensional gas chromatography. Two columns with different stationary phases provide excellent separation for elemental mercury, and multidimensional analysis improves the reliability, performance, and system cleanliness of atomic emission detection. The possibility of false positive identification is substantially eliminated, and excellent sensitivity for the target compound was attained with the use of two selective columns and atomic emission detection at 254 nm. A flame ionization detector was incorporated as part of the system configuration to increase analytical platform capability and flexibility. Elemental mercury was measured in gas matrices over a range of 0.1–170 μg/m3 having a correlation coefficient of R2 = 0.9995, a precision of less than 5% relative standard deviation (n = 10), and a measured recovery exceeding 99% in natural gas as a model matrix. The total analysis time is less than 10 min. Only a small 1 mL sample volume is needed, and the described approach does not rely on any form of sample enrichment. The utility of multidimensional gas chromatography with microwave-induced helium plasma atomic emission spectroscopy is demonstrated with challenging industrial applications, such as the measurement of elemental mercury in natural gas, industrial solvents, and vapor generated from ruptured compact fluorescent light bulbs.

Detection of specific macro and micropollutants in air monitoring: Review of methods and techniques

Abstract The protection of environment, in a specific manner air component, is one of the most important objectives established by national and international organizations. Air pollutants are generally detected by electronic instrumentation containing dedicated units from capturing to processing and displaying. With the deterioration of anthropic activities due to, for example, increasing of car traffic, increasing of heavy industrial activities, and subsequent greenhouse effects, the nature of required value becomes very complex and attention must be paid to “stealth” pollutants and mechanisms that produce them. That is why, beyond traditional pollutants, attention must be paid to specific classes of pollutants such as dusts vectoring fixed in inodorous gases, and other components included in gaseous substances as dioxins and furans. This paper illustrates results of experimental activities within a review approach for detecting pollutants based on advanced technology using nanoparticle through helium microwave-induced plasma, sensors exploiting perovskite structures and thermography for detecting harmful gases. Long-term detection of dioxins is also illustrated.

Three-dimensional simulation of microwave-induced helium plasma under atmospheric pressure

A three-dimensional model is presented to investigate helium plasma generated by microwave under atmospheric pressure in this paper, which includes the physical processes of electromagnetic wave propagation, electron and heavy species transport, gas flow, and heat transfer. The model is based on the fluid approximation calculation and local thermodynamic equilibrium assumption. The simulation results demonstrate that the maxima of the electron density and gas temperature are 4.79 × 1017 m−3 and 1667 K, respectively, for the operating conditions with microwave power of 500 W, gas flow rate of 20 l/min, and initial gas temperature of 500 K. The electromagnetic field distribution in the plasma source is obtained by solving Helmholtz equation. Electric field strength of 2.97 × 104 V/m is obtained. There is a broad variation on microwave power, gas flow rate, and initial gas temperature to obtain deeper information about the changes of the electron density and gas temperature.

Effect of temperature on direct chemical vapor generation for plasma optical emission spectrometry: An application of programmable temperature spray chamber

A new approach based on a programmable temperature spray chamber (PTSC) is described that extends the analytical capability of a direct chemical vapor generation technique (DCVG) by affecting the sensitivity of measurements by both microwave induced plasma (MIP) and inductively coupled plasma (ICP) optical emission spectrometry. Examination of DCVG process and instrumental conditions was performed to characterize the new approach when coupled with the robust and non-robust argon ICP, and helium or argon low-power MIP. Hence, a real comparison between four examined plasma spectrometry systems may be attained based on determination of hydride-forming elements including As, Se and Sb, and Hg forming atomic vapor as well as iodine forming molecular vapor. All observed trends are discussed and explained so that the influence of analyte vapor generation process on analytical figures of merit clearly may be distinguished from that of the water aerosol and vapor delivery process.The main advantage of the DCVG system based on PTSC is its full compatibility with conventional pneumatic nebulization system used in plasma spectrometric techniques, and the improvement in determination of elements that are released from aqueous solutions as easily volatile species. In order to improve the sensitivity, the PTSC was either cooled at 0°C in the case of MIP-OES or electrically-heated at 60°C when coupled with the ICP-OES. For ICP-OES, a slight improvement in sensitivity with increasing temperature was observed due to increased sample delivery rate to the plasma rather than that due to increased analyte vapor generation efficiency. With PTSC, the figures of merit by ICP-OES are improved for all analytes studied comparing with those by ICP-OES with a conventional solution nebulization. The LODs obtained for As, Se, Sb, Hg and I were 5, 5.4, 2.7, 0.085 and 9μgL−1, respectively.Concerning DCVG-PN-PTSC-MIP-OES system, a predominant role of the analyte vapor generation efficiency on the analytical performance was found rather than increased analyte transport efficiency. The beneficial effect of the analyte vapor release is enhanced, however, by combination with reduction of the water loading to the plasma by PTSC cooling. The performance of the DCVG-PN-PTSC-He MIP-OES system was evaluated by determining LODs, which are 20, 14, 19, 2.5 and 8μgL−1 for As, Se, Sb, Hg, and I, respectively.

Gas chromatography plasma-assisted reaction chemical ionization mass spectrometry for quantitative detection of bromine in organic compounds.

We have recently introduced plasma-assisted reaction chemical ionization mass spectrometry (PARCI-MS) for elemental analysis of halogens in organic compounds. Here, we utilize gas chromatography (GC) coupled to PARCI-MS to investigate the mechanism of Br(-) ion generation from organobromines and to evaluate analytical performance of PARCI for organobromine analysis. Bromine atoms in compounds eluting from GC are converted to HBr in a low-pressure microwave induced helium plasma with trace amounts of hydrogen added as a reaction gas. Ionization is achieved by introducing nitrogen into the afterglow region of the plasma, liberating electrons via penning ionization and leading to formation of negative ions. We demonstrate that N2 largely affects the ionization process, whereas H2 affects both the ionization process and in-plasma reactions. Our investigations also suggest that dissociative electron capture is the main ionization route for formation of Br(-) ions. Importantly, GC-PARCI-MS shows a uniform response factor for bromine across brominated compounds of drastically different chemical structures, confirming PARCI's ability to quantify organobromines in the absence of compound-specific standards. Over 3 orders of magnitude linear dynamic range is demonstrated for bromine quantification. We report a detection limit of 29 fg of bromine on-column, ~4-fold better than inductively coupled plasma-MS.

Plasma-Assisted Reaction Chemical Ionization for Elemental Mass Spectrometry of Organohalogens

We present plasma-assisted reaction chemical ionization (PARCI) for elemental analysis of halogens in organic compounds. Organohalogens are broken down to simple halogen-containing molecules (e.g., HBr) in a helium microwave-induced plasma followed by negative mode chemical ionization (CI) in the afterglow region. The reagent ions for CI originate from penning ionization of gases (e.g., N2) introduced into the afterglow region. The performance of PARCI-mass spectrometry (MS) is evaluated using flow injection analyses of organobromines, demonstrating 5-8 times better sensitivities compared with inductively coupled plasma MS. We show that compound-dependent sensitivities in PARCI-MS mainly arise from sample introduction biases.

Detection of Fine-particles in Suspension by Time-resolved Helium Microwave-induced Plasma Atomic Emission Spectrometry

微粒子（≤10000 nm）の組成はじめ構成元素や粒子の数とその大きさを同時に測定する方法を開発するために，表面波励起型のOkamoto cavityを用いて，大電力領域（≤700 W）で生成した大気圧ヘリウムマイクロ波誘導プラズマ（He-MIP）に微粒子を導入して励起・発光させたときの基本特性を，時間分解原子発光分析法を用いて検討した．微粒子を純水中に分散させて懸濁液とし，これをネブライザーで霧化してHe-MIPの中心部に導入した．このときの各微粒子からの発光パルスを複数の分光器を用いて時間分解すると，その同期性から組成が，その波長から元素が，そのパルスの数から粒子数が，そしてその強度から粒子径が分かる．微粒子としてはAg（メジアン径: 368, 518, 833, 1304 nm）とAl2O3（409 nm）とBaTiO3（2062 nm）及びFly-Ash（BCR-038, 5413 nm，成分: As, Cl, Co, Cr etc.）を用いた．この方法によって，懸濁液中のこれらの微粒子を高感度で検出することができた．

Determination of mercury in water samples by electrochemical cold vapor generation coupled to microstrip microwave induced helium plasma optical emission spectrometry

A new combination of flow-through electrochemical mercury cold vapor generation using a microstrip microwave plasma optical emission spectrometry is described in this work. This coupled technique has been optimized to attain the maximum sensitivity for Hg determinations in aqueous solutions and the lower limits of detection. A laboratory constructed thin-layer flow-through hydrogen remover (inner volume of 2×150μL) was used.A limit of detection of 1.1ng·mL−1 (peak height, 3σ criterion) for mercury was obtained with the proposed method when using electrochemical mercury cold vapor generation. Further, the results obtained with spiked SRM NIST 1640 and SRM NIST 2781 were verified by ICP–OES and a good agreement at the concentration levels of 2.72±0.37μg·g−1 and 2.80±0.25μg·g−1 was obtained.The repeatability at the 50ng·mL−1 level was better than 2.7% (RSD).

Speciation analysis of triethyl‐lead and tributyl‐tin compounds in human urine by liquid–liquid extraction and gas chromatography microwave‐induced plasma atomic emission detection

This work describes the development of a fast method for speciation analysis of triethyl-lead and tributyl-tin species in urine samples after in situ derivatization by tetraethyl- or tetrapropyl-borate reagents. The alkylation reaction is done in the aqueous and urine medium and the less-polar derivatives are extracted in hexane by liquid-liquid extraction. The species were extracted and the extract was efficiently collected from the aqueous phase after centrifugation. Finally, the organometallic species are separated by gas chromatography and determined from the emission signals of elemental lead and tin. Atomic lead and tin are formed from the organolead and organotin compounds during atomization of the column eluate in a microwave-induced helium plasma source. The simultaneous measurement of lead (Pb) at 405.780 nm and tin (Sn) at 303.419 nm was achieved by an atomic emission detector. Finally, the analytes were determined with satisfactory precision (<5%) and detection limits of 0.05 μg Pb/L and 0.48 μg Sn/L, respectively, when 10 mL of urine is extracted with 1 mL of hexane and 1 μL of extract is injected.

Helium Microwave-Induced Plasma at Atmospheric Pressure Generated by Okamoto Cavity for Nonmetal Analysis

SUMMARY Helium microwave-induced plasma (He-MIP) for nonmetal elements analysis was generated by a 2.45 GHz microwave power (∼1 kW) with the Okamoto cavity of the surface-wave mode at atmospheric pressure. Effects of the main parameters of the cavity such as the thickness (direction of the electric field) of the cavity, the width of the ring-slot, and the position of the discharge tube (torch) on the excitation temperature and the analytical signals were investigated. The excitation temperature and the electron density of the plasma as a parameter of the microwave power, and the plasma and carrier gas flow rates were measured. With 600-W input microwave power, an excitation temperature of 7000 K for the high energy part and an electron density of 2.4 were obtained. An aqueous solution of NaF was introduced into the center of the annular He-MIP, the F I line (685 nm, 14.5 eV) signal was detected, and the effects of microwave power and the gas flow rates on the signal were studied. A detection limit of 60 ppb for fluorine was obtained.

Cavity Ring-Down Spectroscopy coupled with helium microwave-induced plasma for fluorine detection

Cavity Ring-Down Spectroscopy with a tunable diode laser has been used for the detection of fluorine at trace levels. A homemade experimental setup was constructed to accommodate the microwave-induced plasma glow discharge inside the optical cavity. The energy delivered by helium plasma discharge was successfully used not only for the dissociation of fluorine molecules but, more importantly, also for the excitation of fluorine atoms into their metastable level 3s 4P 5/2. The absorption observed at the 3s 4P 5/2–3p 4D o 7/2 transition (corresponding to a 685.603-nm atomic line) was used for fluorine atom detection. Good agreement between theoretical and measured absorption line shapes confirmed the selectivity of fluorine atomic absorption. We observed an absorption coefficient of 4 ∙ 10 − 6 cm − 1, corresponding to a detection of F(3s 4P 5/2) atoms at about 1.5 ∙ 10 6 atoms cm − 3. These data demonstrate that we achieved a detection limit of 100 ng g − 1 under the conditions of our initial homemade experimental setup. However, the optimization of the system may lead to the improvement of the detection limit by approximately two orders of magnitude.

A low-flow low-power helium microwave induced plasma for optical and mass spectrometry with solution nebulization

A low-flow low-power annular-shaped microwave induced helium plasma operating at atmospheric pressure has been developed for use in optical emission as well as mass spectrometry. The first study on the plasma formation and fundamental investigation of the plasma generated at helium flow rate below 3 L min−1 by the new TEM cavity based MIP system is described. Radial profiles of emission spectra provide He excitation temperature (Texc) of 3000–3300K and electron number density (ne) of 5.5–7.5 × 1014 cm−3. To demonstrate the plasma robustness, both the tolerance for water loading and the excitation capability for metals and nonmetals were investigated using ultrasonic nebulization for wet aerosol introduction into the plasma. Detection limits data are shown for some elements and compared with those obtained using other MIP systems.

Detection of Aqueous Fluoride with a High-Power Microwave-Induced Helium Plasma at Atmospheric Pressure

Detection of Aqueous Fluoride with a High-Power Microwave-Induced Helium Plasma at Atmospheric Pressure

Spectroscopic diagnostics for evaluation of the analytical potential of argon + helium microwave-induced plasma with solution nebulization

An Ar + He mixed-gas microwave-induced plasma (MIP) has been investigated for use as an excitation source for optical emission spectrometry (OES) with solution nebulization. Regarding spectroscopic diagnostics via plasma temperatures and electron number density, the study compares excitation conditions in Ar, He and Ar + He plasma. Spatial emission profiles and radial distribution of electron number density have been determined to study energy transfer in the plasmas. The addition of He to Ar produces a plasma capable of ionizing metals with ionization potential in the range of 6–10 eV more efficiently than the pure Ar plasma. The best excitation conditions for metallic elements were obtained with the Ar + 20% He plasma due to increase of rotational temperature up to 3900 K and argon excitation temperature up to 7500 K as well as Mg II/Mg I line intensity ratio. The detection limits for ionic lines of some metals for the Ar + He mixed-gas plasma are 2–7 times lower than for Ar-MIP-OES.

非金属元素分析のためのヘリウム大気圧マイクロ波プラズマ発光分光分析法

The accurate determination of trace elements in steel is an important and challenging task in analytical chemistry. The variation of the contents of nonmetal elements such as C, P and S in steel can have a significant influence on the mechanical and physical properties. A sensitive and accurate method for the determination of these elements in steels is therefore required.The aim of the present work is to develop an accurate method using He-MIP AES (Helium Microwave-Induced Plasma Atomic Emission Spectrometry) to determine the trace amounts of these elements in the gas, liquid and solid samples. The optimization of the He-MIP AES technique and its analytical figures of merit, as well as its application to the determination of these elements in the samples, were described. The samples were transported and excited in a microwave induced helium plasma operated at atmospheric pressure.A high-power (∼1000 watt CW, 2.45 GHz) annular-shaped microwave-induced helium plasma (He-MIP) was developed for the determination of nonmetals in the aqueous solutions, and the characteristics were presented. The plasma was generated at atmospheric pressure by an Okamoto cavity of the surface wave mode. No external cooling was used to stabilize the plasma. The electron density and iron-excitation temperature were on the order of 1014/cm3 and 6500K, respectively. An air for gas sample was aspirated with an aspirator and introduced directly into the He-MIP. Carbon (247.9 nm) in the air was detected. An aqueous solution was injected into the plasma by an ultrasonic system with desolvation and condensation. Introduction of aqueous fluoride in the form of NaF, chloride in the form of NaCl and bromide in the form of KBr produced intense emission and detection limits of 100 ppb for FI (685.6 nm), Cl II (479.5 nm) and 150 ppb for Br II (470.5 nm) were obtained. Detection limits of the carbon and phosphorous in the aqueous solution were 1 ppb and 2 ppb, respectively.

High-Power Microwave-Induced Helium Plasma at Atmospheric Pressure for Trace Element Analysis

An annular helium plasma at atmospheric pressure was generated by the 2.45 GHz microwave power (∼1 kW) with Okamoto cavity, and the physical and analytical characteristics were summarized. The electron density and iron excitation temperature of high energy part for the He plasma were on the order of 1014/cm3 and 6,500 K, respectively. An aqueous solution with non-metal was injected into the plasma by the ultrasonic system with desolvation and condensation. Intense atomic and/or ionic emissions were detected and the detection limit of 100 ppb for F I (685.6 nm), 100 ppb for Cl II (479.5 nm), 150 ppb for Br II (487.5 nm), 1ppb for C I (247.9 nm), 2 ppb for P I (213.6 nm) and 0.02 ppb for Mg II (279.6 nm) and Ca II (393.4 nm) were obtained.

Recent Advances in Gas Chromatographic/Atomic Emission Hetero-Atom Selective Detection for Characterization of Petroleum Streams and Products

Abstract The selective detection of organo-compounds containing hetero-atoms is used extensively in the petroleum industry for process control (sulfur, nitrogen, etc.) and additives in fuels (sulfur, nitrogen, oxygen, phosphorous, etc.). The most common selective atom detection is performed with atomic emission (AED), sulfur/nitrogen chemiluminescence (SCD, NCD), and photometric (FPD, p-FPD). Atomic emission detection has an advantage over the other selective detectors since in an automated analysis scheme several hetero-elements may be detected for rapid sample screening. This paper describes the unique capabilities of atomic emission detection of fuels and petroleum fractions using several applications. In addition, a simplified version of comprehensive GCxGC that enhances hetero-atom selectivity by significantly reducing the matrix interference from the large hydrocarbon background is coupled with a microwave induced helium plasma atomic emission detector (GCxGC/AED). The GCxGC uses simple valve based flow modulation optimized for samples with a boiling point in the gasoline and jet fuel range. The technique is useful for screening fuels additives, contaminants, etc.

Development of Gas-Phase Sample-Introduction Techniques for Analytical Atomic Spectrometry

For the last 30 years, several types of gas-phase sample-introduction methods in analytical atomic spectrometry, i.e., atomic absorption spectrometry (AAS), atomic emission spectrometry (AES) and atomic fluorescence spectrometry (AFS), have been investigated and developed in the author's laboratory. Their fundamental results are summarized in this review article. The gas-phase sample-introduction techniques developed in the author's laboratory can be roughly divided into four groups: i) hydride generation, ii) cold-vapor generation of mercury, iii) analyte volatilization reactions and iv) miscellaneous. The analytical figures of merit of the gas-phase sample-introduction methods have been described in detail. Hydride generation has been coupled with the AAS of As, Bi, Ge, Pb, Sb, Se, Sn and Te, with the inductively coupled plasma (ICP) AES of As, Bi, Sn, Se and Sb, with the high-power nitrogen microwave-induced plasma (N2-MIP) AES of As, Bi, Pb, Sb, Se, Sn and Te by their single- and multi-element determinations, with the AFS of As, Bi, Pb, Sb, Se, Sn and Te, and with the ICP mass spectrometry (MS) of As and Se. The cold-vapor generation method for Hg has been combined with atmospheric-pressure helium microwave-induced plasma (He- or Ar-MIP)-AES and AFS. Furthermore, analyte volatilization reactions have been employed in the ICP-AES of iodine, in the He-MIP-AES of iodine bromine, chlorine, sulfur and carbon, and in the ICP-MS of sulfur. As a result, when compared with conventional solution nebulization, a great improvement in the sensitivity has been attained in each instance. In addition, the developed techniques coupled with analytical atomic spectrometry have been successfully applied to the determination of trace elements in a variety of practical samples.

Moderate volatility analyte transport behavior with membrane desolvation reversed-phase liquid chromatography-helium microwave-induced plasma atomic emission spectroscopy

The transport behavior of moderately volatile analyte in a membrane desolvation system is examined. With the goal of atomic emission determination of liquid chromatographic analytes, a tubular polytetrafluoroethylene membrane desolvator interface was used to enhance the performance of a 120 W helium microwave-induced plasma atomic emission detector. To monitor organo-chlorine compounds, Cl emission was observed at 479.5 nm. Membrane desolvator conditions such as temperature, solvent composition and counter current gas flow were optimized. Converse to required conditions for non-volatile inorganic compounds, semi-volatile organic compound transport was maximized at lower membrane desolvator temperatures. Analyte transport was enhanced by modifying the solvent with dilute H 2SO 4. Low vapor pressure H 2SO 4 minimized analyte diffusion across the membrane and helped linearize the calibration plot. The detection limit of 2,6-dichlorobenzamide in pure methanol using ultrasonic nebulization and membrane desolvation with microwave-induced plasma detection was 2 ppm. Chromatographic separation and detection was demonstrated with 2,6-dichlorobenzamide and 4-chlorobenzamide.