An evaluation of ion-atom emission intensity ratios and local thermodynamic equilibrium in an argon inductively coupled plasma

Spatially resolved, radial electron density (n_e) profiles have been measured at rf power settings of 0.75, 1.25 and 1.75 kW, and vertical heights of 4,8,12,16,20 and 24 mm above the load coil. These measured values of n_e have been used to construct a theoretical local thermal equilibrium (LTE) framework. Ion-atom emission intensity ratios for Mg and Cd calculated from this framework have been compared to experimentally measured values. The measured ion-atom emission intensity ratios are found to be (ess than calculated LTE ratios. This suggests that the aerosol channel of the inductively coupled plasma can be characterized as an ionizing plasma.     

A spatial study of electron density and analyte emission in a d.c. argon plasma

Spatially resolved electron density measurements have been performed on a three-electrode d.c. plasma using a linear photodiode array based spectrometer. The electron density values measured are between 1× 10¹⁵ and 1 × 10¹⁶ cm^?3 depending on spatial position. The spatial distribution of Ca I (422.7 nm) and Ca II (393.4 nm) emission has also been measured and the Ca II-Ca I emission intensity ratio evaluated. Using the n_e values measured, an analagous LTE ratio has been calculated and this has been compared to the experimental values. Measured ratios are found to be from 28 to 100 times less than LTE ratios. Some possible sources leading to these infrathermal ratios are discussed.     

Atomic emission spectroscopy method for mixing studies in high power thermal plasmas

Atomic emission spectrometry was used to measure the distribution of concentration ratios and temperature in thermal plasmas produced by high power torches for process engineering. The spectroscopic method is based on absolute line intensity measurement and Abel inversion. Assuming local thermal equilibrium, the temperature is deduced from the absolute emission of an argon line and the concentration ratio is deduced from the emission ratio of two lines. Using the two dimensions of the camera for spatial and spectral resolution, fast measurements with high resolution can be done. The method has been tested on a 60 kW inductively coupled plasma torch at atmospheric pressure. The results show that the concentration ratios n(O)/n(Ar) and n(H)/n(Ar) can be measured with an accuracy of 25% and that errors due to deviations from LTE are small. Demixing occurs in the induction zone. The application of the method showed that hydrogen diffuses much more than oxygen. The main disadvantage of this method is that, using emission, it does not permit to measure the concentration in the “cold” zones in the center and at the edge of the plasma.     

Spatial profiles of electron density in the inductively coupled plasma

Spatially resolved, radial electron number density (n_e) profiles have been measured at rf power settings of 1.00, 1.25, 1.50, 1.75 and 2.00 kW, and vertical heights of 4, 8, 12, 16 and 20 mm above the load coil. These profiles have been condensed and presented as electron density contour plots for each input power. The precision of the method was evaluated by doing ten replicate measurements of electron density. The relative standard deviation varied between 2 and 10 % with the maximum at the plasma centre. Electron density was measured with and without the presence of the easily ionizable element—Cs, and no significant difference was observed.     

The rf input power dependence of chromium excited state level populations in the inductively coupled plasma

Excited state level populations have been measured for Cr(I) and Cr(II) in the inductively coupled plasma. The measurement was carried out using a 4096 pixel linear photodiode array spectrometer to detect emission intensities from 16 atomic and 16 ionic lines. The effect of changes in rf input power on the level populations was studied over the power range 0.75-1.75 kW. The results are consistent with a p-LTE model of excitation and ionization.     

Multi-photon ionization in the mass spectrometry of polyatomic molecules: Cross sections

Multi-photon ionization (MPI) with tunable visible/UV laser light is shown to be a sensitive tool for analysis of traces in gas mixtures when combined with a mass spectrometer. Mass spectra of six different organic molecules, obtained with low intensity laser light, are presented and demonstrate the facility of ionization without fragmentation (soft ionization) under proper experimental conditions. Quantitative values for the cross sections for both two photon steps are obtained from the measured intensity dependence and the absolute ion numbers. Such quantitative data help in the evaluation and definition of this new ionization technique in mass spectrometry. Efficiencies of ionization for some molecules are as high as 25% leading to 10⁶ ions in a single pulse from the dye laser (1 kW). Detectability as low as 2 parts in 10⁹ is thus predicted.     

Determination of neutron fluence using the plot of isotope variation of cadmium and gadolinium

The method described to determine the neutron fluence is based on the plot of the isotopic variation of Cd and Gd subjected to neutron irradiation in a research reactor. The isotopic ratios are measured by thermal ionization mass spectrometry. The results indicate that the fluence values obtained, using the variation in the ratios¹¹⁴Cd/¹¹³Cd,¹⁵⁶Gd/¹⁵⁵Gd and¹⁵⁸Gd/¹⁵⁷Gd show standard deviations varying from 0.3 to 6.6%. These values agree with the extrapolated values calculated using the short time Au activation method. The method appears to be useful for determining paleo neutron flux in natural samples and irradiated fuels.     

Some considerations regarding temperature,electron density,and ionization in the argon inductively coupled plasma

The measured density of electrons in the ICP cannot be explained on the basis of a pure LTE calculation. A mechanism which involves radiation trapping and the transfer of excitation energy from the annular regions of the ICP to the aerosol channel is offered. This mechanism called “assisted ionization” leads to a more accurate prediction of electron density at a particular temperature. Assisted ionization is the result of the coupling of high energy resonance radiation from Ar(I) in the annular regions of the ICP into the analyte channel. The response of analyte atoms and ions to temperature and electron density in the channel can be estimated by inclusion of the analyte ionization equilibrium in an overall equilibrium which includes argon atoms and excited state argon species.     

Detection of iron species using inductively coupled plasma mass spectrometry under cold plasma temperature conditions

Under the conditions of low radio frequency (rf) power of 600 W and aerosol gas flow rate of 1.25–1.35 l/min, ⁵⁶Fe (or ⁵⁴Fe) ions can be detected from the isobaric interference of the ArO⁺ (or ArN⁺) matrix. Using this method, the detection limit of ⁵⁶Fe can reach 16 ng/l (ppt), 60 times smaller than by normal plasma conditions at 1200 W rf power. The linear dynamic range of the analyte measurement extends to 1000 ng/ml (ppb).     

Energy-transfer processes in decaying helium-cadmium plasmas

Light absorption and emission spectroscopy were used in studies of the time dependences of the CdII spectral emission and He^m(2³S) number density in the stationary afterglow of helium-cadmium mixtures. Transitions from 12 CdII energy levels were monitored in the afterglow. The five CdII states below 20 eV are produced, either directly or via cascading, by the Penning ionization of Cd by He^m(2³S). The remaining CdII states studied are produced by the chargeexchange excitation of Cd by He⁺. No evidence was found for the production of CdII energy levels by charge transfer between Cd and He ₂ ⁺ or by Penning ionization of Cd by He ₂ ^m (2³ _u ⁺ ). A value of (5.4±0.3)×10^–10 cm³ sec^–1 was measured for the reaction rate coefficient for the Penning ionization of Cd by He^m(2³S), and a value of (2.1±0.2)×10^–10 cm³ sec^–1 was measured for the reaction rate coefficient for charge exchange between He⁺ and Cd at a gas temperature of 200°C.     

Spatial profile measurement of electron number densities and analyte line intensities in an inductively coupled plasma

A versatile instrument for spatial profile measurement has been developed and applied to the measurement of electron number densities and analyte emission intensities in an inductively coupled plasma (ICP). A precise Y-Z stage on which the ICP source was mounted was set on a rail-based optical bench. By translating the ICP source with a precision of ± 0.01 mm, the H_β Stark broadening and analyte line intensities were measured with the use of a silicon intensified target (SIT) and a photomultiplier (PMT). Micro-computer assisted data acquisition allowed it to measure a large number of emission profiles in a short period. The ease of acquisition enabled to build up complete contour maps of electron number densities, Ca neutral atom (Ca I) and Ca ion (Ca II) line intensities, and intensity ratios of the Ca II and Ca I lines. The maximum electron number density was 4 × 10¹⁵ cm^?3 occurring low in the plasma and 5 mm off axis. In a contour map of the electron number densities a hollow region was found low in the plasma, and the distribution pattern looked like a deep “trench”. Along the central channel of the ICP, the peak position of Ca II emission occurred higher than that of Ca I emission, and the spatial distribution of Ca II emission was wider and taller than that of Ca I emission. It has been verified that Ca I is emitted mainly at the region where the electron number density is less than 1 × 10¹⁴ cm^?3.     

Implementation of acoustic, radiofrequency and microwave rotating fields in analytical plasma sources

Four helium plasma sources operating at atmospheric pressure have been developed for analytical emission spectrometry by applying a synchronically rotating field with three or more phases operating at 1 kHz, 27 MHz or 2.45 GHz. The plasma takes the form of a disk and has minimum field strength at the axis. Thus, a channel is formed at the center through which the sample in the form of wet aerosol or a chemically generated vapor of halogen may be introduced. A dual-flow concentric ceramic injector was used to supply helium plasma gas and the sample to the plasma. The helium plasma operated at low power levels (40-300 W) and low gas flow rates of below 3 L min^− 1 and was self-igniting. The acoustic, radio-frequency (rf) and microwave-driven plasmas can withstand wet aerosol loadings of 5, 30 and 100 mg min^− 1, respectively, generated by an ultrasonic nebulizer without a desolvation unit. The plasma physical characteristics were compared at these three frequencies under otherwise similar operating conditions. The helium excitation temperature, OH rotational temperature and electron number density increased with increasing frequency in ranges of 2800-4000 K, 1100-3200 K and 0.1-7 × 10¹⁴ cm^− 3, respectively. To demonstrate the effect of frequency on the plasma excitation efficiency the emission intensity from halogen ions was evaluated using chemical vapor generation with continuous sampling without desiccation. Using 3-phase microwave, 6-phase microwave, 4-phase rf and 1 kHz helium plasma sources the detection limits (3σ) for chlorine at 479.40 nm were 26, 60, 230 and 1200 ng mL^− 1, respectively. The microwave-driven plasma was the densest and had the highest excitation potential toward chlorine and bromine ions.     

Attachment and ionization in a self-consistent treatment of the electron kinetics of a collision-dominated rf plasma

This paper deals with the self-consistent determination of the rf field amplitude for sustaining the steady-state collision-dominated weakley ionized plasmas in the bulk of the rf discharge and of the time-resolved behavior of the isotropic part of the distribution function as well as of relevant macroscopic quantities in plasmas whose particle loss is dominantly determined by electron attachment. The strict timeresolved treatment is based on the nonstationary Boltzmann equation of the electrons and its numerical solution including, apart from electron number conservative collision processes, the electron attachment and ionization. The investigations are related to an rf plasma in a model gas and in SF₆ and are performed for reduced rf field frequencies around 10 MHz Torr^–1 which are of particular interest from the point of application of rf discharges for plasma processing. The numerical results show that a large field amplitude of around 160 V cm^–1 Torr^–1 is necessary to maintain the discharge and that the isotropic distribution, the relevant collision frequencies for attachment and ionization, and the electron density undergo a large modulation during a period of the rf field.     

Evaluation of the detection capability of a U-shaped d.c. arc for spectrometric analysis of solutions

A gas-stabilized arc with aerosol supply, originally designed for atomic absorption studies, has been used for emission spectrometric analysis of solutions. A characteristic of the arc is a fairly long horizontal part of the arc column which makes possible “end-on” observation of the spectral emission and selection of a well-defined region of the arc column for analysis. The most intense emission of continuum is at the arc column axis while the emission maxima of the nebulized elements are located at different distances from the axis, which mainly depend on the ionization potential of the corresponding element.The presence of alkali elements in the arc plasma enhance considerably the spectral emission of the elements with medium and low ionization potentials. The effect depends mainly on the first ionization potential of the element and its extent is approximately the same for atom and ion lines. In the case of potassium chloride the intensity increase approaches a plateau at a concentration of 2.5 mg ml^?1. The magnitude of the effect justifies the use of potassium chloride as a spectroscopic buffer.Detection limits obtained with this source on 60 spectral lines are compared with those found in inductively coupled plasmas and in an inverted V-arc echelle spectrometer system. Comparison reveals that inductively coupled plasmas yield consistently lower detection limits with the ion lines used, while with the atom lines it retains the advantage only for elements having a high ionization potential.     

Hydrogen/argon plasma jet with methane addition

Spatial distributions of plasma parameters are presented for a H₂/Ar plasma jet with addition of methane. The plasma has been generated at atmospheric pressure by a 200 A (20 kW) nontransferred do arc. Optical emission spectroscopy has been used for the measurements assuming the plasma jet to be optically thin and to have an axial symmetry. Local spectral ernissivity values have been evaluated using a routine Abel inversion procedure. Half- width and emissivity of H spectral line have been measured to determine the electron density and temperature of the plasma. The densities of excited C, CH radicals have been evaluated from the absolute emissivities of relevant molecular emission bands measured in limited spectral intervals in the visible spectrum. The emissivity ratios have been used to fund rotational and vibrational temperatures. The results supply information on methane decomposition and the behavior of molecular radicals in close-to-thermal plasma jets.     

Negative chemical ionization in quadrupole ion trap mass spectrometry: Effects of applied voltages and reaction times

The effects of applied voltages and reaction times on negative ion chemical ionization in the quadrupole ion trap are investigated. Mass-selected ejection of undesired reagent ions and selective mass storage of only negative ions are required for practical negative ion chemical ionization. This is achieved by application of rf and dc voltages to the ring electrode to control the mass-to-charge ratios one polarity) of ions stored, as well as by application of a supplemental rf voltage applied across the endcap electrodes to selectively eject ions of a particular mass-to-charge ratio. Even with careful control of these parameters, negative chemical ionization is not as sensitive as electron ionization and positive chemical ionization because of the lack of thermal electrons in the ion trap. Mass selection of the hydroxide anion as a reagent ion and exclusion of all positive ions provide [M ? H]^? ions with little or no fragmentation for a wide variety of compounds.     

Evaluation eines Elektronendiffusionsmodelles zur Berechnung von nicht Gleichgewichts-Elektronenkonzentrationen in Induktiv gekoppelten Argonplasma für die spektrochemische Analyse

The electron density in argon ICP discharges has been found experimentally by other investigators to be higher than that calculated from the temperature distribution and Saha equation assuming local thermodynamic equilibrium (LTE). The results of the present study suggest that this non equilibrium concentration has mainly two causes: first, the kinetic energy of electrons owing to the power input of the rf field is higher than the kinetic energy of the gas particles. Second, as an effect of the extremely high gradients in the electron density and the temperature distribution, ambipolar diffusion of electrons results in a non LTE situation. With the help of the ambipolar diffusion constant and with recombination being taken into account, the electron concentration and the electron temperature in an ICP have been calculated. The so calculated electron density distributions are compared with literature values, found experimentally by other investigators. Finally a new model is proposed which explains the high ion concentration found experimentally for important analytical species.     

Comparison of mass spectrometric and optical measurements of temperature and electron density in the inductively coupled plasma during mass spectrometric sampling

Electron density (n_e) and ionization temperature (T_ion) are measured using atomic emission spectrometry (AES) from the small funnel of gas just outside the sampling orifice of an inductively coupled plasma-mass spectrometer (ICP-MS). Rotational temperature (T_rot) is measured using an OH emission band. T_ion is also determined for the same elements (Zn and Cd) by using M⁺ ion signal ratios by MS. For matrix-free solutions, typical values are n_e=1.6×10¹⁵ cm⁻³, T_rot=3340 K, T_ion (MS)≈T_ion (AES)≈7000 K. This agreement between the T_ion values supports other observations that, for atomic analyte ions M⁺ of similar m/z values in matrix-free solutions, the relative signals in the mass spectrum reflect the corresponding relative abundances in the ICP region being drawn into the sampler. Using either MS or AES, T_ion for Cd is 300–400 K higher than that for Zn, which indicates that T_ion can vary for different elements in the ICP. Sodium nitrate matrix at levels up to 1000 ppm Na does not cause a measurable change in n_e; 2000 ppm Na causes n_e to increase to 2.1×10¹⁵ cm⁻³. Sodium matrix has a large effect on the MS signal levels but does not greatly change the resulting T_ion values measured optically.     

Temporal evolution of lead isotope ratios and metal concentrations in sediments of the north Aegean Sea,in Turkish coast

In present research, fifteen surficial and two profile sediment samples were studied in terms of sediment chronology and pollution degree on the ground of pollution indexes such as enrichment factor (EF), contamination factor (CF), Pollution Load Index (PLI) and lead isotope ratios (²⁰⁶Pb/²⁰⁷Pb, ²⁰⁸Pb/²⁰⁶Pb). Lead-210 (polonium-210) activity concentrations were measured by utilizing alpha spectrometry. Sediment chronology was determined via modified CRS mathematical model. Average mass accumulation rates are 0.301 and 0.227 g cm^?2 year^?1 in Bak?rçay River mouth and Ayval?k offshore stations respectively. Mass accumulation rates do not display the systematic increases along the cores from bottom layers to top layers. In Bak?rçay River mouth station ²¹⁰Pb flux is higher than the range of global atmospheric ²¹⁰Pb flux value. Due to the high CF and EF values of Sr both of stations have hydrothermal features. Ayval?k offshore station has displayed Na, Cd pollution since 1945, but Na, Cd, As, Mo, Ag pollutions have existed in Bak?rçay River mouth station since 1983 in terms of CF and EF values. According to PLI index, Bak?rçay River mouth station has “starting level pollution” degree and it displayed an “acute corruption” in 1981. ²⁰⁶Pb/²⁰⁷Pb ratios range from 1.17 to 1.25, ²⁰⁸Pb/²⁰⁶Pb ratios range from 1.99 to 2.16 in study area. When ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁶Pb ratios are evaluated with together, it is seen that both of the stations have had the natural (geologic) sediments since 2011.     

The vertical spatial characteristics of analyte emission in the inductively coupled plasma

Utilizing a photodiode array based spatial profiling spectrometer vertical spatial profiles of analyte emission have been measured for a large number of neutral atom and ion lines in the inductively coupled plasma. The lines can be subdivided into two basic categories. One group (called “ soft ” lines after Boumans) have spatial emission behaviour that is very dependent on power, aerosol flow and analyte excitation and ionization characteristics. The second group (called “ hard ” lines after Boumans) have spatial emission behaviour that is relatively insensitive to all of the above parameters. In all cases ion lines have hard line behaviour as do the more energetic atom lines. Under fixed ICP conditions all hard lines have their peak emission at essentially the same position in the discharge which is always higher in the discharge than that for soft lines. It is also shown that the spatial behaviour of soft lines can be directly correlated with normal temperature.