Real-time analysis of CuO by inductively coupled plasma emission without external calibration

The study of a method, devoted to real-time detection of metallic pollutants present in stack gas, is investigated. This method is based on spectroanalysis using an inductively coupled plasma (ICP) emission system without external calibration. The fluidized bed technology is employed to inject metallic species into the ICP emission. The mass fluxes of copper oxide (CuO) are then determined by using the intensity ratios of the metallic element spectral lines with those of the plasma gas element (argon or dry air). These ratios and the plasma characteristics (atomic excitation temperature, degree of thermal disequilibrium θ=T_e/T_h) are inserted into a calculation code of plasma composition to determine the mass flux. The results are in good agreement using either argon plasma or dry air plasma. A study of the fluidized bed properties is made to compare our values with those resulting from the elutriation calculation of the copper oxide.     

Computer simulation of RF induction-heated argon plasma discharges at atmospheric pressure for spectrochemical analysis-I. preliminary investigations

Models of induction coupled plasma (ICP) discharges are developed for arrangements important in spectrochemical analysis. These models account for the spatial distribution of gas properties and major energy losses found in high temperature discharges. Realistic gas flows, and sample particle motion and decomposition are incorporated into the models. Computer simulations based on these models provide spatial temperature, gas velocity, sample concentration, and radiation distributions for a number of experimental ICP discharge configurations. The alteration of these distributions for various operational parameters permits evaluation of some important factors in developing spectroohemical analysis with the ICP source. Recognized differences between theory and experiment are discussed.     

The effects of natural moisture and of argon addition on the plasma temperature and on the detection limits of an apparatus for online control of metal pollutants by air inductively coupled plasma

New results are presented concerning an apparatus for continuous monitoring of metal pollutants in air by the atomic emission spectroscopy (AES) method using an air inductively coupled plasma (ICP). Problems connected with the important role of the accuracy of the calibration method and with the incidence on calibration of the parameters of the calibration device are discussed. The incidence on the plasma characteristics, of the water introduced in the discharge by the calibration process, of the water brought in with the ambient air for analysis and of alkali metal salts introduced in the discharge, is analysed. The effect on the discharge parameters, such as the local excitation temperature in the analytic zone and the thermal equilibrium of the plasma, was measured. A method to improve the detection limits (DL) is presented. This method is suitable for analytes simultaneously characterized by high toxicity (low threshold limit values (TLV)) and by atomic analytic lines with a high excitation energy (low sensitivity in low temperature air discharges). It has been shown that using a mixture of 50% air+50% argon (total flow rate 15 l min⁻¹) gives a sufficient sample of air for analysis and appreciably lowers the DL.     

Low flow,externally air cooled torch for inductively coupled plasma atomic emission spectrometry with axial viewing

The torch wall is cooled largely by air passing through a cooling jacket added to the outside of a Fassel torch. The plasma is viewed axially through a cooled cone interface centered on the axial channel. The outer argon gas flow can be reduced to 7 l min⁻¹ with no compromise in performance or torch lifetime. The plasma exhibits the same ‘robustness index’ and interference effects from Na as the conventional, high-flow ICP supplied with the particular spectrometer used. Detection limits (DL) for lines at ∼200 nm are poorer by approximately a factor of two, while those for lines at ∼400 nm are actually better than values typically seen for the same lines by axial viewing of a conventional, high-flow ICP.     

Analytical inductively coupled nitrogen and air plasmas

The operation of inductively coupled plasmas generated at atmospheric pressure in nitrogen or air in a modified 18 mm i.d. quartz tube assembly is evaluated for the analysis of aqueous solutions and fine powders. The instrumentation and detailed procedure for the generation of molecular-gas discharges are described. Limits of detection for nitrogen and air ICP discharges are compared, and for five elements at the same wavelength the nitrogen ICP produced significantly poorer values than the air plasma. The air ICP provided comparable values to those reported in the literature for argon. The sensitivity, signal-to-background ratio, and limits of detection for calcium were compared for argon, air, and argon with air central gas discharges with pneumatic and ultrasonic nebulization and for airborne calcium carbonate powders.     

Preparation and characterization of a set of IAEA reference air filters for quality control in air-pollution studies

Several sets of reference air filters were prepared as part of an IAEA evaluation of the performance of laboratories involved in air-pollution studies. Each set comprised three polycarbonate membrane filters, two of which were loaded with urban air particulate matter (APM) obtained in Vienna or Prague, and one unloaded filter. The filters were loaded by filtration of a suspension of the APM materials in water. The homogeneity both of bulk APM materials and of the loaded filters was evaluated and found suitable by determining several elements by instrumental neutron-activation analysis (INAA), proton-induced X-ray emission (PIXE), and micro-X-ray energy-dispersive fluorescence analysis (μ-EDXRF). After evaluation of the homogeneity, INAA, PIXE, EDXRF, atomic absorption spectrometry (AAS), inductively coupled plasma optical emission spectrometry (ICP–OES), and ICP mass spectrometry (ICP–MS) were used to characterize the filter materials and establish “target values” and their associated standard deviations for 15 elements. Problems encountered during the preparation of these unique, simulated air filters and the criteria for setting both the target values and standard deviations are presented.     

Comparison of simulated and experimental fundamental ICP parameters

False-color spatial maps of experimentally determined and simulated values of electron number density (n_e), electron temperature (T_e) and heavy-particle temperature (T_g) for an argon inductively coupled plasma (ICP) in the plasma decay region (tail flame) are compared in detail. Experimental and theoretical values are in general very consistent; the difference between experiment and computation is approximately 10% for n_e and T_e and 20% for T_g in the plasma region examined. The errors in n_e and T_e are larger at the edge of the plasma, most likely because air entrainment becomes significant. This comparison provides a link between measurements and the current mathematical model and serves to partially validate both methods. Sources of error in both experiment and theory are considered and discussed.     

Introduction of organic/hydro-organic matrices in inductively coupled plasma optical emission spectrometry and mass spectrometry: A tutorial review. Part I. Theoretical considerations

Due to their outstanding analytical performances, inductively coupled plasma optical emission spectrometry (ICP-OES) and mass spectrometry (ICP-MS) are widely used for multi-elemental measurements and also for isotopic characterization in the case of ICP-MS. While most studies are carried out in aqueous matrices, applications involving organic/hydro-organic matrices become increasingly widespread. This kind of matrices is introduced in ICP based instruments when classical “matrix removal” approaches such as acid digestion or extraction procedures cannot be implemented. Due to the physico-chemical properties of organic/hydro-organic matrices and their associated effects on instrumentation and analytical performances, their introduction into ICP sources is particularly challenging and has become a full topic. In this framework, numerous theoretical and phenomenological studies of these effects have been performed in the past, mainly by ICP-OES, while recent literature is more focused on applications and associated instrumental developments. This tutorial review, divided in two parts, explores the rich literature related to the introduction of organic/hydro-organic matrices in ICP-OES and ICP-MS. The present Part I, provides theoretical considerations in connection with the physico-chemical properties of organic/hydro-organic matrices, in order to better understand the induced phenomena. This focal point is divided in four chapters highlighting: (i) the impact of organic/hydro-organic matrices from aerosol generation to atomization/excitation/ionization processes; (ii) the production of carbon molecular constituents and their spatial distribution in the plasma with respect to analytes repartition; (iii) the subsequent modifications of plasma fundamental properties; and (iv) the resulting spectroscopic and non spectroscopic interferences. This first part of this tutorial review is addressed either to beginners or to more experienced scientists who are interested in the analysis of organic/hydro-organic matrices by ICP sources and would like to consider the theoretical background of effects induced by such matrices.     

Can we predict the structure and stability of molecular crystals under increased pressure? First‐principles study of glycine phase transitions

The aim of this study was to determine whether the periodic density functional theory (DFT) calculations can be used for accurate prediction of the influence of the increased pressure on crystal structure and stability of molecular solids. To achieve this goal a series of geometry optimization and thermodynamic parameters calculations were performed for γ‐glycine and δ‐glycine structures at different pressure values using CASTEP program. In order to perform most accurate geometry optimization various exchange‐correlation functionals defined within generalized gradient approximation (GGA): PBE, PW91, RPBE, WC, PBESOL as well as defined within local density approximation (LDA), i.e. CAPZ, were tested. Geometry optimization was carried out using different dispersion correction methods (i.e. Grimme, TS, OBS) or without them. The linear response density functional perturbation theory (DFPT) was used to obtain the phonon dispersion curves and phonon density of states from which thermodynamic parameters, such as: free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) were evaluated. The results of the geometry optimization depend strongly on the choice of the DFT functional. Calculated differences between the free energy of the studied polymorphic forms at the studied pressure values were consistent with experimental observations on their stability. The computations of thermodynamic properties not only confirmed the order of stability of two studied forms, but also enabled to predict the pressure at which this order is reversed. The results obtained in this study have proven that the plane‐wave basis set first principles calculations under periodic conditions is suitable for accurate prediction of crystal structure and stability. © 2018 Wiley Periodicals, Inc.     

An active spectroscopical study on the plasma parameters of an ICP

Various techniques to measure the electron density and temperature of a 100 MHz inductively coupled plasma (ICP) are compared with each other. Apart from passive spectroscopy of measuring the shape of (e.g. H(beta)) and the area under emission lines we explored the field of active spectroscopy. Non-intrusive and specific are the methods of diode laser absorption (DLA) of an argon 4s-4p transition and Thomson scattering (TS). Intrusive and global is the power interruption (PI) technique: the response of line (argon and analytes) and continuum emission is followed during PI. Finally, a combination of two active techniques, namely TS during PI, is studied. By using the different techniques on the same plasma condition (frequency, power and flows) this intercomparison will reveal the validity region of the various techniques. In this way a strong basis will be created for understanding plasma phenomena.     

Introduction of organic/hydro-organic matrices in inductively coupled plasma optical emission spectrometry and mass spectrometry: A tutorial review. Part II. Practical considerations

Inductively coupled plasma optical emission spectrometry (ICP-OES) and mass spectrometry (ICP-MS) are increasingly used to carry out analyses in organic/hydro-organic matrices. The introduction of such matrices into ICP sources is particularly challenging and can be the cause of numerous drawbacks. This tutorial review, divided in two parts, explores the rich literature related to the introduction of organic/hydro-organic matrices in ICP sources. Part I provided theoretical considerations associated with the physico-chemical properties of such matrices, in an attempt to understand the induced phenomena. Part II of this tutorial review is dedicated to more practical considerations on instrumentation, instrumental and operating parameters, as well as analytical strategies for elemental quantification in such matrices.     

Some theoretical and practical considerations to the application of linear photodiode arrays for inductively coupled plasma emission spectrometry

Expressions are developed and used to predict the performance of a linear photodiode array when used with a conventional dispersive spectrometer for inductively coupled plasma (ICP) atomic emission spectrometry in the 200 to 450 nm region. The photon flux from the ICP and the relative standard deviation (RSD) at high concentrations are used in the equations to calculate the degradation of performance to be expected at and above the detection limit for integration times up to 10 s. Significant degradation is predicted only below 230 nm, and this degradation is less than a factor of 10 at 200 nm for an ICP with an RSD of 0.2 %. One-second integration times are possible with noiser ICPs or at longer wavelengths without significant performance degradation by the photodiode array.     

Artificial Intelligence Computation to Establish Relationships Between APS Process Parameters and Alumina–Titania Coating Properties

Modeling the behavior of air plasma spray (APS) process, one of the challenges nowadays is to identify the parameter interdependencies, correlations and individual effects on coating properties, characteristics and influences on the in-service properties. APS modeling requires a global approach which considers the relationships between coating characteristics/ in-service properties and process parameters. Such an approach permits to reduce the development costs. This is why a robust methodology is needed to study these interrelated effects. Artificial intelligence based on fuzzy logic and artificial neural network concepts offers the possibility to develop a global approach to predict the coating characteristics so as to reach the required operating parameters. The model considered coating properties (porosity) and established the relationships with power process parameters (arc current intensity, total plasma gas flow rate, hydrogen content) on the basis of artificial intelligence rules. Consequently, the role and the effects of each power process parameter were discriminated. The specific case of the deposition of alumina–titania (Al₂O₃–TiO₂, 13% by weight) by APS was considered.     

Characterization and screening of metals,metalloids and biomarkers in crude oil by ICP–MS/OES,and GC–MS techniques after digestion by microwave‐induced combustion

A method for digestion of light and medium Iraqi crude oils (Basrah and Khanaken oils) using microwave‐induced combustion (MIC) in closed vessels is described for the determination of Hg, Au, Cu, Al, Ca, Co, K, Mg, Si and Sr by inductively coupled plasma optical emission spectrometry (ICP–OES) and Mo, Ti, Mn, Li, Se^?1, Rb, Ag, Ba, Pb, As, Cd, Cr, Fe, Ni, V and Zn by inductively coupled plasma mass spectrometry (ICP–MS). Upon using MIC it was possible to obtain lower limits of detection by ICP–MS and also by ICP–OES compared with those obtained by microwave‐assisted digestion. The MIC was the best choice with regard to the possibility of using dilute nitric acid as an absorbing solution, which is important to minimize the interference encountered by ICP–MS and ICP–OES.The physicochemical parameters and some contaminants of crude oil samples were analyzed to classify and assess the quality of the crude oils. This study determines the viability of the use of Fourier transform infrared spectroscopy as an alternativee to traditional petroleum geochemical methods for crude oil characterization. The infrared fingerprints agree with the results obtained from GC–MS analysis.     

Can Enantioselectivity be Computed in Enthalpic Barrierless Reactions? The Case of CuI‐Catalyzed Cyclopropanation of Alkenes

An extensive computational study has been carried out on different catalytic systems for cyclopropanation reactions based on copper. Most DFT schemes used present drawbacks that preclude the calculation of accurate absolute kinetic properties (energy barriers) of such systems, excepting the M05 and M06 suites of density functionals. On the other hand, there is a wide range of DFT methods capable of reproducing relative energy values, which can be easily translated into selectivities. Most of the theoretical levels used tend to overestimate activation barriers, allowing the location of the transition state (TS) on the potential-energy surface (PES) of the most reactive systems, which are probably artifacts of the method. However, after a thorough analysis of the calculated PES, and the origin of the energy differences obtained for the different alkene approaches in chiral systems, it is found that energy differences are almost constant over a wide range of geometries covering the reaction channel zone in which the true TS on the Gibbs free-energy surface (GFES) lies. Therefore, many computational schemes can still be used confidently to explain and predict enantioselectivities in these systems.     

Entrainment of ambient air into a spectrochemical inductively coupled argon plasma

A spectrochemical inductively coupled argon plasma (ICP) is normally operated in the open air. Therefore, it is suggested in the literature that entrainment of air molecules into such an ICP may cause loss of electrons, especially so at the plasma's edge. The present study discusses the significance of this effect. The density and temperature of electrons and nitrogen molecules around the edge of the plasma were measured by Thomson and rotational Raman scattering. A region where both electrons and nitrogen were present in detectable amounts (10¹⁹ and 10²⁴ m⁻³, respectively) could not be observed. Above the torch inner wall the nitrogen concentration drops rapidly towards the plasma. Measurements suggest that the nitrogen concentration at 1 mm from the plasma is only a few percent, and in the active zones of the plasma (far) below 0.1%. This is not enough to affect the plasma significantly. Moreover, electron loss due to diffusion of nitrogen into the plasma is calculated to be much slower than the loss observed in earlier studies. Hence, air entrainment is unlikely to play a significant role in the ICP. A possible alternative is the formation and destruction of molecular rare gas ions.     

An active spectroscopical study on the plasma parameters of an ICP

Various techniques to measure the electron density and temperature of a 100 MHz inductively coupled plasma (ICP) are compared with each other. Apart from passive spectroscopy of measuring the shape of (e.g. H) and the area under emission lines we explored the field of active spectroscopy. Non-intrusive and specific are the methods of diode laser absorption (DLA) of an argon 4s-4p transition and Thomson scattering (TS). Intrusive and global is the power interruption (PI) technique: the response of line (argon and analytes) and continuum emission is followed during PI. Finally, a combination of two active techniques, namely TS during PI, is studied. By using the different techniques on the same plasma condition (frequency, power and flows) this intercomparison will reveal the validity region of the various techniques. In this way a strong basis will be created for understanding plasma phenomena.     

A magnetically excited microwave plasma source for atomic emission spectroscopy with performance approaching that of the inductively coupled plasma

A novel magnetically excited microwave plasma emission source was developed and tested. Unlike previous microwave plasma sources which couple energy from the microwave electric field, this source couples energy from the magnetic field. The resultant plasma shape allows easy entrainment of wet sample aerosol, such as is produced by a conventional inductively coupled plasma (ICP) nebulizer and spray chamber, into the core of the plasma. Plasma support gas can be either nitrogen or air although better sensitivity is achieved using nitrogen. Good stability of operation was observed for both aqueous and organic solvents over a wide range of sample flows. The measured performance when used as a spectroscopic source in conjunction with an echelle polychromator showed detection limits approaching those of commercial ICP sources.     

Plasma Spray Process Operating Parameters Optimization Based on Artificial Intelligence

During plasma spray process, many intrinsic operating parameters allow tailoring in-flight particle characteristics (temperature and velocity) by controlling the plasma jet properties, thus affecting the final coating characteristics. Among them, plasma flow mass enthalpy, flow thermal conductivity, momentum density, etc. result from the selection of extrinsic operating parameters such as the plasma torch nozzle geometry, the composition and flow rate of plasma forming gases, the arc current intensity, beside the coupled relationships between those operating parameters make difficult in a full prediction of their effects on coating properties. Moreover, temporal fluctuations (anode wear for example) require “real time” corrections to maintain particle characteristic to targeted values. An expert system is built to optimize and control some of the main extrinsic operating parameters. This expert system includes two parts: (1) an artificial neural network (ANN) which predicts an extrinsic operating window and (2) a fuzzy logic controller (FLC) to control it. The paper details the general architecture of the system, discusses its limits and the typical characteristic times. The result shows that ANN can predict the characteristics of particles in-flight from coating porosity within maximal error 3 and 2 % in temperature and velocity respectively. And ANN also can predict the operating parameters from in-flight particle characteristics with maximal error 2.34, 4.80 and 8.66 % in current intensity, argon flow rate, and hydrogen flow rate respectively.