Central Gas Flow Research Articles

Characterization of ionization and matrix suppression in inductively coupled ‘cold’ plasma mass spectrometry

A parametric study of plasma power and central gas flow was carried out to study the transition from normal analytical conditions to cooler plasma conditions using an inductively coupled plasma mass spectrometer having a balanced load coil. ‘Cold plasma' conditions (low power and high central gas flow) permit the determination of K, Ca and Fe at trace levels. The effect of changing the position of the ground reference of the load coil was investigated. Trace element ionization is consistent with thermal ionization at low electron density. Ion–molecule chemistry (charge transfer) with NO+ or O2+ may be important at the cooler plasma temperature. Suppression of analyte signals by concomitant matrix elements is partially correlated with the ionization potentials of the matrix element. If the analyte ion signals are normalized to that for NO+, the suppression of signals appears to be independent of the matrix element, and a modest dependence on the ionization potential of the analyte element is apparent. For high concentrations of elements of low ionization potential, an additional or enhanced mechanism of ionization is evident. The onset for this enhanced ionization is sharply defined by a characteristic ionization potential near 6.0 eV. The sensitivity for trace elements does not appear to be affected by this enhanced ionization. The appearance of the enhanced ionization is made evident by a change in the ratio of the NO+ and O2+ signals. Use of cold plasma conditions for the determination of K, Ca and Fe in high-purity waters and acids is evident. It appears that the method may also be used for samples having moderate salt content if the analytical protocol includes measurement of the background ions NO+ and O2+.

Fundamental studies of mixed-gas inductively coupled plasmas

The effects of adding foreign gases to the central-gas flow or the intermediate-gas flow of an argon inductively coupled plasma are presented. In particular, the influence of up to 16.7% added helium, nitrogen or hydrogen on radially-resolved electron number density, electron temperature, gas-kinetic temperature and calcium ion emission profiles is examined. It is shown that these gases affect not only the fundamental parameters and bulk properties of the plasma, but also how energy is coupled and transported through the discharge and how that energy interacts with the sample. For example, added helium causes an increase in the gas-kinetic temperature, most likely due to the higher thermal conductivity of helium compared to argon but, in general, does not appear to affect significantly either the electron temperature or electron concentration. The shift in the calcium ion emission profile towards lower regions in the discharge with added helium may be attributable to higher droplet desolvation and particle vaporization rates. In contrast, the addition of nitrogen or hydrogen to an Inductively Coupled Argon Plasma (Ar ICP) results in dramatic changes in all three fundamental plasma parameters: electron number density, electron temperature, and gas-kinetic temperature. The net effect of these molecular gases (N 2 or H 2) on calcium ion emission and on the fundamental plasma parameters is shown to be dependent on the amount of gas added to the plasma and whether the gas is introduced as part of the central- or intermediate-gas flow. In general, nitrogen added to the central-gas flow causes a significant reduction in the number of electrons throughout most of the discharge (over an order of magnitude in certain regions), mainly in the central and upper zones of the ICP. A drop of 3000–5000 K in the central channel electron temperature and a smaller drop in the gas-kinetic temperature are also observed when N 2 is added to the central-gas flow. In contrast, the introduction of nitrogen in the intermediate flow causes about a 1 × 10 15 electrons cm −3 increase in the electron concentration in the low, toroidal regions of the plasma and an increase in the gas-kinetic temperature of around 1000 K throughout most of the discharge. As seen with the addition of nitrogen to the central-gas flow, the electron temperature is found to increase in the toroidal zones of the plasma when N 2 is added to the intermediate flow. These combined effects cause a 20-fold depression in the calcium ion emission intensity only a 1.7-fold depression when N 2 is added to the central- or intermediate-gas flows, respectively. On the other hand, hydrogen causes a depression in the electron concentration in the upper areas of the plasma when this gas is added to the central flow but increases the number of electrons in the same region when added to the intermediate flow. Hydrogen also causes a dramatic effect on the electron and gas-kinetic temperatures, significantly increasing both of these parameters throughout the discharge. An increase in the calcium ion emission intensity, accompanied by a downward shift, elongation and broadening of the calcium ion emission profile is also observed with H 2 addition.

The effect of sample matrix on electron density, electron temperature and gas temperature in the argon inductively coupled plasma examined by Thomson and Rayleigh scattering

Spatially-resolved electron temperature ( T e), electron number density ( n e) and gas-kinetic temperature ( T g) maps of the inductively coupled plasma (ICP) have been obtained for two central-gas flow rates, four heights above the load coil (ALC) and in the presence and absence of interferants with a wide range of first ionization potentials. The radial profiles demonstrate how the directly measured fundamental parameters n e T e and T g can be significantly enhanced and/or depressed with added interferent, depending upon plasma operating conditions and observation region. In general, the magnitude of n e, and T e change is found to be an inverse function of interferent ionization potential; furthermore, n e enhancements in the central channel might be the result of electron redistribution from high to low electron density regions rather than from ionization of the matrix. The large measured increases in n e cannot be attributed solely to matrix ionization, especially when measurement uncertainties and the probable over-estimation in calculated n e, enhancements are taken into account. Changes in n e and T e have been correlated with axial Ca atom and ion emission profiles. A brief review of the mechanisms most likely involved in interelement matrix interferences is given within the context of the present study. This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hardcopy text is accompanied by a disk for the Macintosh computer with data files stored in ASCII format. The main article discusses the scientific aspects of the subject and gives an interpretation of the results contained in the data files.

Characteristics of an inductively coupled argon plasma operating with organic aerosols. Part 2. Axial spatial profiles of solvent and analyte species in a chloroform-loaded plasma

The effect of chloroform load on the axial emission profiles for Mg I, Mg II, C I, C2, and CN was measured. The emission intensity ratio of Mg II : Mg I was used to indicate the ‘robustness’ of the plasma at r.f. powers of 1.0, 1.25, and 1.50 kW and central channel gas flow rates of 0.6–0.9 l min–1 over the accessible range of solvent load. The C2 and CN emissions mark the boundries of the aerosol channel and the edge of the atomic plasma in the ‘tailflame’ region.

Determination of mercury isotope ratios in samples containing sub-nanogram amounts of mercury using inductively coupled plasma mass spectrometry

The determination of sub-nanogram amounts of mercury demands systems of high sensitivity. To determine isotopic ratios a large signal is required to obtain a high number of counted ions. It was found that the precision in the isotope ratio determination in samples containing less than 300 pg of mercury is limited by the counting statistics. With 300 pg of mercury the precision was 0.2%(relative standard deviation) in the 202Hg: 199Hg ratio. The detection limit was lowered by concentration of mercury vapour on gold traps, and the sensitivity of the instrument was increased 4–6-fold by addition of nitrogen or hydrogen to the central gas flow.

Gas pulsation attenuator for automotive air conditioning compressor

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Addition of molecular gases to argon gas flows for the reduction of polyatomic-ion interferences in inductively coupled plasma mass spectrometry

Addition of 1% N2 to the coolant Ar gas flow at a nebulizer gas flow rate of 0.95 dm3 min–1 can eliminate 40Ar35Cl+ and dramatically reduce 35Cl16O+ and 37Cl16O+, without losing sensitivity for a representative analyte, In. Addition of 3% N2 to the central channel gas flow, at a nebulizer gas flow rate of 0.70 dm3 min–1, has the same effects on polyatomic-ion interferences but also results in a loss in sensitivity to some extent. No significant effects on oxides (48Ti16O+, 140Ce16O+, 238U16O+) and doubly charged (138Ba2+) species were observed with or without N2 addition. Addition of CH4 to the Ar gas flows has a similar effect to that of N2 addition, but results in carbon deposition on the sampling cone and a more complicated spectrum. Results of analyte determination for a reference material confirmed that addition of N2 could be applied to real samples.

Behavior of Fines in the Blast Furnace.

Using a half section three-dimensional model of a blast furnace, a tuyere-injection experiment of coke fines was conducted. The following findings were obtained from the analysis of the influence of the injection rate and particle size of the fines on the burden descent and gas permeability and the study of the circulation and deposit behaviors of the fines in the blast furnace. With an increase in the injection rate of fines, the frequency of slips, the gas pressure, and the frequency and extent of the raceway shape variation increased. But the influence of the fines injection was limited when their particle size was much smaller than the size of the charged materials. The injected fines are to be deposited at the surface of the dead-man and near the furnace wall where the burden descent velocity is low. When the high-concentration regions of fines are formed at the surface of the dead-man and near the furnace wall, the burden descent region in the lower part of the furnace reduced and the retention time of the burden decreased. With the V-shaped stock and inadequate central gas flow, fines are likely to be deposited in the center and they descend with the burden.

A comparison of argon and mixed gas plasmas for inductively coupled plasma-mass spectrometry

The effects of adding N 2 to the outer gas flow of an Ar plasma in inductively coupled plasma mass spectrometry (ICP-MS) are illustrated. With 5% N 2 added to the outer gas flow and provided the central (nebulizer) gas flow is increased, modest signal enhancements (up to a factor of 4) are observed. The degree of enhancement depends on the extent to which an element forms a strong metal oxide bond and also, to some extent, on ionization potential. An important feature of N 2 mixed gas plasmas for ICP-MS is that the signals for analyte oxide species (MO +) and certain background species (ArO +, ArOH +, Ar 2 +, ClO +, and ArCl +) are significantly reduced (an order of magnitude) by the addition of N 2 to the outer gas flow. In addition to these observations, some results are also presented for O 2 and air (outer gas) mixed gas plasmas and N 2 (central gas) mixed gas plasmas.

Effect of central gas flow rate and water on an argon inductively coupled plasma: spatially resolved emission, ion-atom intensity ratios and electron number densities

The effect of aqueous aerosol on plasma properties and emission signals was investigated. Plasma behavior was compared when using spark-generated dry sample introduction to that when conventional aqueous aerosol sample introduction was used. The shape of vertical and radial Mg II and Mg I emission profiles were strongly influenced by aqueous aerosol introduction. The Mg II to Mg I emission intensity ratios varied little with radial position or central gas flow rate when dry sample was introduced. However, the emission intensity ratios were strongly dependent on radial position and central gas flow rate when aqueous aerosol was introduced. The Mg II to Mg I emission intensity ratio varied widely with radial position even when measured electron number densities were constant over the same locations. The Mg II to Mg I emission intensity ratios were less than local therrnodynamic equilibrium (LTE) predictions when no water was present. The intensity ratio was close to LTE values when small aqueous aerosol mass transport rates and low central gas flow rates were used but was far below LTE values when typical aerosol mass transport rates were used. Desolvating droplets may be responsible for the observed behavior. Time averaging of droplet-induced signal fluctuations may introduce bias into measurements of plasma properties.

Hydrodynamics of spout-fluid beds

Experiments were carried out in a half-column incorporating auxiliary flow, introduced through up to five slots along a 60° conical base, in addition to a central flow of air. The column had a diameter of 0.15 m and inlet diameters of either 19 or 25 mm. Three different types of particle were investigated, all with mean particle sizes in the 2 – 4 mm range. Four different flow regimes — fixed bed, spouting with aeration, spout-fluidization and jet in a fluidized bed — were identified and mapped. The minimum total gas flow required for spouting with aeration and for spout-fluidization was always greater than that corresponding to minimum spouting. Gas percolation through the annulus increased by as much as 50% as the proportion of auxiliary flow was increased for a given total gas flow rate. Solids circulation was increased somewhat by addition of auxiliary flow for deep beds, but a decrease occurred for shallow beds. The overall bed pressure drop under minimum spouting with aeration conditions increased linearly with auxiliary flow. On the other hand, the fountain height decreased as the fraction of auxiliary flow was increased for a fixed total gas flow, and increased with auxiliary flow for a fixed central gas flow. The empirical correlation of McNab predicted the average spout diameter well if the sum of the central and auxiliary flows was used in the correlation.

Parametric study of the flow and temperature fields in an inductively coupled r.f. plasma torch

A theoretical investigation of the effect of different parameters on the flow and the temperature fields in a radiofrequency inductively coupled plasma is carried out. The parameters studied are: central injection gas flow rate, total gas flow rate, input power, and the type of plasma gas. The results obtained for argon and nitrogen plasmas at atmospheric pressure indicate that the flow and the temperature fields in the coil region, as well as the heat flux to the wall of the plasma confinement tube, are considerably altered by the changes in the torch operating conditions.

New methods of burden distribution control in bell-armour charging.

Under the present situation which is forced to reduce the productivity of the all coke operation, it is important to establish such a distribution adjusting technique as to maintain an adequate peripheral gas flow and a sharp central gas flow simultaneously. The gas distribution in a furnace equipped with a bell-armour in comparison with that of the bell-less top has a tendency to flatten owing to the difference in size segregation behaviour in the radial direction, thus posing a problem in micro-control of the burden distribution.The authors have recently developed a new technique of controlling the burden distribution by the movable armour and applied it to Chiba No. 5 Blast Furnace. The technique is aimed at improving the layer thickness and promoting the particle size segregation in the radial direction, slowing down the raw material discharging rate from the bell by controlling the bell stroke and speed.By the application of this technique, it has made possible to strengthen both the peripheral gas flow and central gas flow simultaneously, and thus has greatly contributed to stabilizing the furnace condition and extention of the permitted limit for operation under the recent circumstances of reduced production.

Use of spatial emission profiles and a nomenclature system as aids in interpreting matrix effects in the low-power argon inductively coupled plasma

An automated profiling system was used to determine vertical intensity distributions for atomic and ionic lines of several elements in the ICP and to measure the effect of matrix components on those distributions. Most atomic lines show maximum signal (not necessarily maximum signal/noise) rather low in the plasma. Ion lines predominate in the plasma region used most frequently for analysis. In the region of high atomic emission, enhancements are observed for both atom and ion lines with many analytes when matrix elements are added. The enhancements either disappear or become much less severe in the region of high ionic emission normally viewed. The zone where the interferences occur can be shifted higher or lower in the plasma depending primarily on the central gas flow and the power level. Plasma structure can be used to predict regions of high interference. A Nomenclature System for the plasma zone is used as an aid in comparing plasma conditions.

A Low Background Beta Counter with a Plastic Scintillator Anticoincidence Shield

The design and performance of a low background beta counter is described. The counter consists of a central gas flow proportional counter surrounded by a large plastic scintillator anticoincidence shield.