The role of the He I and He II metastables in the population of the Sn II,Sn III and Sn IV ion levels

On the basis of the temporal evolutions of the singly, doubly and triply ionized tin (Sn II, Sn III and Sn IV, respectively) spectral line intensities, in the pulsed helium and nitrogen plasmas, the important role of the He I and He II metastables has been observed in the Sn II, Sn III and Sn IV ionization and population processes. According to these processes, one can expect realization of several laser levels in the Sn II (11.07, 11.20, 12.44 and 13.11 eV), Sn III (15.91, 17.82, 19.13 and 20.19 eV) and Sn IV (20.51 eV) spectra. The modified version of the linear, low-pressure, pulsed arc was used as a plasma source operated in helium with tin atoms, as impurities, evaporated from tin cylindrical plates located in the homogenous part of the discharge tube. This plasma source provides good conditions for a generation of the Sn III, Sn IV and Sn V ions at relatively low electron temperatures (below 18,000 K) providing low background radiation around the intense Sn IV and Sn III spectral lines in the helium plasma. The 222.613 ± 0.0005 nm Sn IV line, not observed up to now, has been identified. The marked, but not classified 243.688 nm Sn spectral line is sorted by ionization stages. The shapes of Sn III and Sn IV lines, ranged between 207 nm and 307 nm, have been obtained. At a 17,500 K electron temperature and 1.07 × 10²³ m^− 3 electron density the Stark broadening was found as the dominant mechanism in the mentioned lines broadening. The measured Stark widths of the prominent nine Sn IV and seven Sn III lines are the first data in the literature. The Stark widths of the intense 229.913 nm and 288.766 nm Sn IV lines can be used for the plasma electron density and temperature diagnostics purposes.     

Physical and analytical characteristics of an atmospheric pressure argon–helium radiofrequency capacitively coupled plasma

A very low power radiofrequency capacitively coupled plasma (13.56 MHz, 5–70 W), was generated in our laboratory on a sharp Kanthal tip without any counter electrode, as an intrinsic part of RLC series resonant circuit. Physical characteristics of this plasma obtained in Ar–He mixture, were studied as function of observation height or gas mixture composition. The excitation temperature of Ar (1500–2100 K), He (3000–3500 K) and H (2500–3200 K), the rotational temperature of the OH band (1300–2900 K), the electron temperature (5500–6500 K) and the electron number density (8 · 10¹³–2 · 10¹⁴ cm^− 3) were determined. The evolution of several atomic emission lines or molecular bands was studied in order to investigate the fundamental processes that take place in such plasma. From the point of view of analytical applications it was found that the optimum conditions of excitation (most intense emission lines and lowest detection limits) are met for a 42% He in the gas mixture and an observation height of 1 mm above the electrode. The optimum atomic emission analysis parameters were established for 7 elements (Na, Li, Ca, K, Cd, Zn and Hg) using pneumatically nebulized liquid solutions. It was found that the presence of He in the plasmogenic gas has an enhancing effect on the emission intensities and detection limits.     

Stark broadening of Mg I and Mg II spectral lines and Debye shielding effect in laser induced plasma

We report Stark broadening parameters for three Mg I lines and one Mg II line in the electron number density range (0.67–1.09) · 10¹⁷ cm^− 3 and electron temperature interval (6200–6500) K. The electron density is determined from the half width of hydrogen impurity line, the H_α, while the electron temperature is measured from relative intensities of Mg I or Al II lines using Boltzmann plot technique. The plasma source was induced by Nd:YAG laser radiation at 1.06 μm having pulse width 15 ns and pulse energy 50 mJ. Laser induced plasma is generated in front of a solid state surface. High speed photography is used to determine time of plasma decay with good homogeneity and then applied line self-absorption test and Abel inversion procedure. The details of data acquisition and data processing are described and illustrated with typical examples. The experimental results are compared with two sets of semiclassical calculations and the results of this comparison for Mg I lines are not unambiguous while for Mg II 448.1 nm line, the results of Dimitrijević and Sahal-Bréchot calculations agree well with our and other experimental results in the temperature range (5000–12,000) K and these theoretical results are recommended for plasma diagnostic purposes. The study of line shapes within Mg I 383.53 nm multiplet shows that the use of Debye shielding correction improves the agreement between theoretical and experimental Stark broadening parameters.     

On the stoichiometry of mass transfer from solid to plasma during pulsed laser ablation of brass

We have performed spectroscopic analysis of the plasma produced by pulsed laser ablation of brass in a low pressure argon atmosphere. The intensities of several spectral lines of copper, zinc and lead were measured for succeeding laser pulses applied to the same irradiation site. The intensities and spectral shapes of the observed transitions were compared to the spectral radiance computed for plasma in local thermal equilibrium. At a delay of 600 ns after the laser pulse, the plasma is characterized by typical values of temperature and electron density of 1.1 × 10⁴ K and 1.2 × 10¹⁷ cm^− 3, respectively, and an elemental composition equal to that of the sample. Small changes of spectral line intensities were observed with increasing number of applied laser pulses. They were attributed to the alteration of the plume expansion dynamics as a consequence of crater formation on the sample surface. The results indicate that the mass transfer from the solid to the plasma is stoichiometric.     

Determination of the Rb atomic number density in dense rubidium vapors by absorption measurements of Rb2 triplet bands

A simple and accurate way of determining atom number densities in dense rubidium vapors is presented. The method relies on the experimental finding that the reduced absorption coefficients of the Rb triplet satellite bands between 740 nm and 750 nm and the triplet diffuse band between 600 nm and 610 nm are not temperature dependent in the range between 600 K and 800 K. Therefore, the absolute values of the reduced absorption coefficients of these molecular bands can provide accurate information about atomic number density of the vapor. The rubidium absorption spectrum was measured by spatially resolved white-light absorption in overheated rubidium vapor generated in a heat pipe oven. The absolute values for the reduced absorption coefficients of the triplet bands were determined at lower vapor densities, by using an accurate expression for the reduced absorption coefficient in the quasistatic wing of the Rb D1 line, and measured triplet satellite bands to the resonance wing optical depth ratio. These triplet satellite band data were used to calibrate in absolute scale the reduced absorption coefficients of the triplet diffuse band at higher temperatures. The obtained values for the reduced absorption coefficient of these Rb molecular features can be used for accurate determination of rubidium atomic number densities in the range from about 5 × 10¹⁶ cm^− 3 to 1 × 10¹⁸ cm^− 3.     

On the Stark broadening in the Au I and Au II spectra from a helium plasma

The Stark FWHM (Full-Width at Half of the Maximal line intensity, W) of 5 neutral and 26 singly ionized gold (Au I and Au II, respectively) spectral lines have been measured in laboratory helium plasma at approximately 16,600 K electron temperature and 7.4 × 10²² m^− 3 electron density. Five Au I and ten Au II W values are reported for the first time. The Au II W values are compared with recent theoretical data, calculated based on a modified semi-empirical approach, and also with existing experimental W values. Our normalized Stark widths are six times higher than those measured in a laser-produced plasma. Possible explanation of this is recommended here. An agreement (within the accuracy of the experiment and uncertainties of the theoretical approach used) with the recently calculated W data was found in the 6p–7s Au II transition. The calculated hyperfine splitting for the five Au II lines in the 6s–6p transition is also presented. At the stated helium plasma conditions, Stark broadening has been found to be the dominant mechanism in the Au I and Au II line shape formation. A modified version of the linear low-pressure pulsed arc was used as a plasma source operated in helium, with gold atoms as impurities evaporated from the thin gold cylindrical plates located in the homogeneous part of the discharge, providing conditions free of self-absorption. This plasma source ensures good conditions for generation of excited gold ions due to Penning and charge exchange effects.     

Low power cross-flow atmospheric pressure Ar + He plasma jet : Spectroscopic diagnostic and excitation capabilities

A cross-flow atmospheric plasma jet with distilled water or analyte solution nebulization has been investigated. The plasma gas flows perpendicularly to the RF powered electrode (11.21 MHz) and a grounded electrode was added for plasma stabilization. The working parameters of the plasma generator can be controlled in order to maximize either the plasma power (75 W) or the voltage on the RF powered electrode (plasma power, 40 W). The plasma gas, pure argon (0.4 l min⁻¹) or a mixture of argon (0.3–0.4 l min⁻¹) and helium (0–0.2 l min⁻¹), was also used for liquid nebulization. Optical emission of the plasma, collected in the normal viewing mode, was used for plasma diagnostics and for evaluating its excitation capabilities. The influence of helium content in the mixed-gas plasma on the plasma characteristics and on the emission axial profiles of the plasma gas constituents and of the analytes originate from the wet aerosol was studied. The addition of helium to the argon plasma, generally determines decreases in the emission of the plasma gas constituents (with the exception of molecular nitrogen), in the rotational temperature and in the electron number density and increases in the excitation temperatures and in the emission of easily excitable analytes. Based on the determined electron number densities, it was concluded that in the plasma zone which presents interest from analytical point of view the plasma is not very far from the partial thermodynamic equilibrium. In function of the helium content in the plasma gas and of the axial distance from the powered electrode the excitation temperatures are in the range of 2420–3340 K for argon, 2500–5450 K for oxygen and 900–2610 K for ionic calcium and the electron number densities are in the range of 1.2 10¹²–1.25 10¹³ cm⁻³. Some elements with excitation energy lower than 6 eV were excited in the plasma. The plasma excitation capability depends on the working conditions of the plasma generator (maximum power or maximum voltage on the RF powered electrode) and on the helium content in the mixed-gas plasma. The estimated detection limits for the studied elements (Na, Li, K, Ca, Cu, Ag, Cd, Hg and Zn) are in the range of 7 ng ml⁻¹ to 28 μg ml⁻¹.     

Time-resolved optical emission spectroscopic measurements of He plasma induced by a high-power CO2 pulsed laser

Laser-induced breakdown spectroscopy of helium plasma, initially at room temperature and pressures ranging from 12 to 101 kPa was investigated using a transverse excitation atmospheric CO₂ pulsed laser (λ = 9.621 and 10.591 μm, a full width at half maximum of 64 ns, and an intensity from 1.5 to 5.36 GW cm⁻²). The helium breakdown spectrum is mainly due to electronic relaxation of excited He, He⁺ and H. Plasma characteristics were examined in detail on the emission lines of He and He⁺ by the time-integrated and time-resolved optical emission spectroscopy technique. Optical breakdown threshold intensities, ionization degree and plasma temperatures were obtained. An auxiliary metal mesh target was used to analyze the temporal evolution of the species in the plasma. The results show a faster decay of the continuum emission and He⁺ species than in the case of neutral He atoms. The velocity and kinetic energy distributions for He and He⁺ species were obtained from time-of-flight measurements. Electron density in the laser-induced plasma was estimated from the analysis of spectral data at various times from the laser pulse incidence. Temporal evolution of electron density has been used for the estimation of the three-body electron-ion recombination rate constant.     

A spectroscopic study of laser-induced tin–lead plasma: Transition probabilities for spectral lines of Sn I

In this paper, we present transition probabilities for 97 spectral lines of Sn I, corresponding to transitions n(n = 6,7,8)s → 5p², n(n = 5,6,7)d → 5p², 5p³ → 5p², n(n = 7)p → 6s, determined by measuring the intensities of the emission lines of a Laser-induced breakdown (emission) spectrometry (LIBS). The optical emission spectroscopy from a laser-induced plasma generated by a 10 640 Å radiation, with an irradiance of 1.4 × 10¹⁰ Wcm^− 2 on an Sn–Pb alloy (an Sn content of approximately 20%), in vacuum, was recorded at 0.8 µs, and analysed between 1900 and 7000 Å. The population-level distribution and corresponding temperature were obtained using Boltzmann plots. The electron density of the plasma was determined using well-known Stark broadening parameters of spectral lines. The plasma under study had an electron temperature of 13,200 K and an electron number density of 2 × 10¹⁶ cm^− 3. The experimental relative transition probabilities were put on an absolute scale using the branching ratio method to calculate Sn I multiplet transition probabilities from available radiative lifetime data of their upper states and plotting the Sn I emission spectrum lines on a Boltzmann plot assuming local thermodynamic equilibrium (LTE) to be valid and following Boltzmann's law. The LTE conditions and plasma homogeneity have been checked. Special attention was paid to the possible self-absorption of the different transitions. The experimental results obtained have been compared with the experimental values given by other authors.     

Optical emission spectroscopy diagnostics of inductively-driven plasmas in argon gas at low pressures

An optical emission spectroscopy method for determination of electron temperature, electron density and gas temperature is developed and applied for diagnostics of inductively-driven argon discharges in a cylindrical geometry. The discharges are maintained at frequency 27 MHz, applied power varied in the limits P = (90 – 160) W and gas pressure in the range p = (1.1 – 117.3) Pa. The method combines measurements of emission spectral line intensities and profile broadenings with a collisional-radiative model of argon plasma at low pressure. The model is employed for investigation of the plasma kinetics governing the population densities of 3p⁵4s and 3p⁵4p argon configuration levels, treated separately. In the numerical calculations the electron density and electron temperature are varied whereas the values of the third plasma parameter — the gas temperature — are involved as obtained data from the experiments. Comparison of the experimental results of the line-intensity ratios with those calculated by the model yields the values of the electron density and temperature. The dependence of the electron temperature, electron density and gas temperature on the discharge conditions is obtained and discussed in the study.     

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.     

Measured Stark widths of several spectral lines of Pb III

The Stark full widths at half of the maximal line intensity (FWHM, ω) have been measured for 25 spectral lines of Pb III (15 measured for the first time) arising from the 5d¹⁰6s8s, 5d¹⁰6s7p, 5d¹⁰6s5f and 5d¹⁰6s5g electronic configurations, in a lead plasma produced by ablation with a Nd:YAG laser. The optical emission spectroscopy from a laser-induced plasma generated by a 10 640 Å radiation, with an irradiance of 2 × 10¹⁰ W cm^− 2 on a lead target (99.99% purity) in an atmosphere of argon was analysed in the wavelength interval between 2000 and 7000 Å. The broadening parameters were obtained with the target placed in argon atmosphere at 6 Torr and 400 ns after each laser light pulse, which provides appropriate measurement conditions. A Boltzmann plot was used to obtain the plasma temperature (21,400 K) and published values of the Stark widths in Pb I, Pb II and Pb III to obtain the electron number density (7 × 10¹⁶ cm^− 3); with these values, the plasma composition was determined by means of the Saha equation. Local Thermodynamic Equilibrium (LTE) conditions and plasma homogeneity has been checked. Special attention was dedicated to the possible self-absorption of the different transitions. Comparison of the new results with recent available data is also presented.     

Atomic transition probabilities for selected Yb II lines emitted from a ferroelectric plasma source

The relative intensities of several hundred emission lines of Yb II between 200 nm and 900 nm were obtained with the use of ferroelectric plasma source. These relative intensities obtained for lines from 21 energy levels have been used to determine the line branching fractions, which have then been combined with accurate experimental radiative lifetime measurements to give absolute transition probabilities for 111 Yb II lines. The obtained values were compared with theoretical and experimental data taken from available literature.     

Temporally resolved laser induced plasma diagnostics of single crystal silicon — Effects of ambient pressure

Laser-Induced Breakdown Spectroscopy of silicon was performed using a nanosecond pulsed frequency doubled Nd:YAG (532 nm) laser. The temporal evolution of the laser ablation plumes in air at atmospheric pressure and at an ambient pressure of ∼ 10^− 5 mbar is presented. Electron densities were determined from the Stark broadening of the Si (I) 288.16 nm emission line. Electron densities in the range of 6.91 × 10¹⁷ to 1.29 × 10¹⁹ cm^− 3 at atmospheric pressure and 1.68 × 10¹⁷ to 3.02 × 10¹⁹ cm^− 3 under vacuum were observed. Electron excitation temperatures were obtained from the line to continuum ratios and yielded temperatures in the range 7600–18,200 K at atmospheric pressure, and 8020–18,200 K under vacuum. The plasma morphology is also characterized with respect to time in both pressure regimes.     

Study of a new direct current atmospheric pressure glow discharge in helium

In this study a new DC-APGD operated in He was developed and characterized. The discharge is operated at 0.9 kV and about 25-35 mA and at a gas flow of 100 ml/min. The source was spectroscopically studied and parameters such as the rotational temperature (T_rot), the excitation temperature (T_exc), the ionization temperature (T_ion) and the electron number density (n_e) were determined. The current-voltage characteristic of the source was studied as well. At optimized conditions the discharge operates in the normal region of the current-voltage characteristic. Rotational and excitation temperatures determined with the use of OH band and Fe I lines as thermometric species were of the order of about 900-1200 and 4500-5500 K, respectively. This indicates that despite of the atmospheric pressure, the discharge is not in LTE. Spatially resolved temperature measurements were performed with axial as well as radial resolution and showed relatively flat profiles. Axially resolved emission intensity profiles for several species such as H, N₂, N₂⁺, OH, He and Hg were determined. It also was found that H₂ introduced into the He by electrolysis of acid solutions such as in ECHG considerably increases the spectroscopically measured gas temperatures but decreases the analyte line intensities, as shown for Hg.     

Effect of a transverse magnetic field on the plume emission in laser-produced plasma: An atomic analysis

We have investigated the effect of varying transverse magnetic field on the plasma plume emission of laser-produced lithium plasma. Two atomic transitions for lithium neutral Li (I) and two for Li ion LI (II) are taken for the study. It has been found that for Li (I), the emission from 670.8 nm transition (2s²S_1/2←2p²P_3/2′1/2) shows initial enhancement and then subsequent decrease for higher fields. Of course, the overall intensity is increased for all the fields when compared to the case of without field. On the other hand, for 610.3 nm (2p²P_1/2←3d²P_3/2′5/2), there is continuous decrease in intensity. Interestingly, for Li (II) transitions also, after an initial increase in intensity up to 0.08 Ta decrease is observed. From the atomic analysis, we find that for 670.8 nm line, the cause of initial enhancement is increase in electron impact excitation whereas for decreased intensity, increased field-induced ionization appears to be responsible mechanism. However, for 610.3 nm line, decrease in intensity appears to be due to decreased recombination. For Li (II), 478.8 nm (3p¹P₁←4d¹D₂) and 548.4 nm (2s³S₁←2p³P_2,1,0) transitions, initial increase appears to be due to increased confinement (increase in plasma density) and subsequent decrease in intensity with increase in field due to decreased recombination.     

Photographic plasma images and electron number density as well as electron temperature mappings of a plasma sustained with a modified argon microwave plasma torch (MPT) measured by spatially resolved Thomson scattering

In this work the determination of electron number densities and electron temperatures for the case of a modified microwave plasma torch (MPT) operated at 100 W with argon by means of spatially resolved Thomson scattering measurements and photographic records of the MPT at different working conditions are reported. With an internal gas flow of 500 ml min⁻¹ and an outer gas flow of 200 ml min⁻¹ electron number densities and electron temperatures are in the range of 10²⁰ m⁻³ to 10²¹ m⁻³ and of 16 000–18 000 K, respectively. When increasing the internal gas flow from 500 to 900 ml min⁻¹ the plasma becomes longer and the maximum electron number density increases by a factor of 2. An increase of the outer gas flow from 200 to 700 ml min⁻¹ leads to a lifting of the whole plasma from the burner edge with the maximum electron number density remaining unchanged. An increase of the power from 80 to 180 W was found to lead to higher electron number densities whereas the electron temperatures remain unchanged. The addition of 1.2 mg min⁻¹ of water vapor to the internal gas flow leads to a decrease of the electron number density from 4.7×10²⁰ m⁻³ to 2×10²⁰ m⁻³ and to an increase of the electron temperature from 16 000 to 22 000 K. In order to document the influence of the internal gas flow rate, water introduction and introduction of easily ionized elements on the visible plasma shape digitally recorded photos of the plasma are presented.     

Application of laser-induced plasma spectroscopy to the measurement of Stark broadening parameters

In this work, we have studied the main conditions that a laser-induced plasma must fulfill in order to be considered as adequate for the measurement of Stark broadening parameters. We investigated the effect of the temporal window, the self-absorption, the crater size, and the effect of the spatial inhomogeneity on the emission profiles coming from a laser-induced plasma. Starting from the spatially resolved values of the plasma parameters, obtained by emission spectroscopy, the error in the determination of the Stark electron width due to the spatial inhomogeneity has been estimated and, for the present experimental conditions, was found to be lower than 7%. As a test of the method, the Stark electron broadening constant of Fe I 381.58 nm has been measured using the Fe I 538.34 nm emission line as the reference to determine the electron density. The plasma was produced under a controlled atmosphere of argon at atmospheric pressure, on an iron–nickel alloy sample. The emission was collected by a system with high spectral resolution, for different temporal windows after the laser pulse. For time delays between 2.75 and 21 μs, the electron density showed an evolution in the range 2.0–0.13 × 10¹⁷ cm^− 3, while the temperature varied from 11 100 to 7100 K. The representation of the Stark electron width of Fe I 381.58 nm, measured for each temporal window, versus the Stark electron width of the reference line showed a linear behavior with a high correlation coefficient. From the slope of this linear fit and the Stark electron broadening constant of the reference line, the Stark width of Fe I 381.58 nm was obtained to be 1.10 ± 0.07 × 10^− 2 nm for an electron density of 10¹⁷ cm^− 3.     

Quantification of Aluminum Gallium Arsenide (AlGaAs) Wafer Plasma Using Calibration-Free Laser-Induced Breakdown Spectroscopy (CF-LIBS)

In this work, we report the results of the compositional analysis of an aluminum gallium arsenide (AlGaAs) sample using the calibration-free laser-induced breakdown spectroscopy (CF-LIBS) technique. The AlGaAs sample was doped with three various concentrations of gallium (Ga), arsenic (As), and aluminum (Al), as reported by the manufacturer, and the CF-LIBS technique was employed to identify the doping concentration. A pulsed Q-switched Nd: YAG laser capable of delivering 200 and 400 mJ energy at 532 and 1064 nm, respectively, was focused on the target sample for ablation, and the resulting emission spectra were captured using a LIBS 2000+ spectrometer covering the spectral range from 200 to 720 nm. The emission spectra of the AlGaAs sample yielded spectral lines of Ga, As, and Al. These lines were further used to calculate the plasma parameters, including electron temperature and electron number density. The Boltzmann plot method was used to calculate the electron temperature, and the average electron temperature was found to be 5744 ± 500 K. Furthermore, the electron number density was calculated from the Stark-broadened line profile method, and the average number density was calculated to be 6.5 × 10¹⁷ cm⁻³. It is further observed that the plasma parameters including electron temperature and electron number density have an increasing trend with laser irradiance and a decreasing trend along the plume length up to 2 mm. Finally, the elemental concentrations in terms of weight percentage using the CF-LIBS method were calculated to be Ga: 94%, Al: 4.77% and As: 1.23% for sample-1; Ga: 95.63%, Al: 1.15% and As: 3.22% for sample-2; and Ga: 97.32%, Al: 0.69% and As: 1.99% for sample-3. The certified concentrations were Ga: 95%, Al: 3% and As: 2% for sample-1; Ga: 96.05%, Al: 1% and As: 2.95% for sample-2; and Ga: 97.32%, Al: 0.69% and As: 1.99% for sample-3. The concentrations measured by CF-LIBS showed good agreement with the certified values reported by the manufacturer. These findings suggest that the CF-LIBS technique opens up an avenue for the industrial application of LIBS, where quantitative/qualitative analysis of the material is highly desirable.     

Optimization of operating conditions of axially and radially viewed plasmas for the determination of trace element concentrations from ultrasound-assisted digests of soil samples contaminated by lead pellets

The method of ultrasound-assisted extraction followed by inductively coupled plasma optical emission spectrometry (ICP-OES) used for the determination of trace element concentrations (arsenic, copper, lead, antimony, and zinc) in shooting range areas was optimized. Optimization was achieved not only on the basis of the analysis of appropriate standard reference materials but also on that of 31 synthetic mixtures of matrix and analyte elements (aluminum, antimony, arsenic, calcium, copper, lead, iron, manganese, silicon, and zinc), in five concentrations. All the measurements were performed in robust plasma conditions which were tested by measuring the Mg II 280.270 nm/Mg I 285.213 nm line intensity ratio. The highest Mg II 280.270 nm/Mg I 285.213 nm line intensity ratios were observed when a nebulizer gas flow of 0.8 L min⁻¹, auxiliary gas flow of 0.2 L min⁻¹ and plasma power of 1400 W were used for both the axially and radially viewed plasmas. The analysis of 31 synthetic mixtures of the selected elements showed that As concentrations could be accurately determined with axially viewed plasma alone. The determination of Pb and Sb could be performed with either axially or radially viewed plasma whereas, surprisingly, Cu could be determined with high accuracy using radial plasma alone with a power of 1400 W. All the elements investigated were determined with high accuracy using robust plasma conditions and a combination of axially and radially viewed plasmas. The total recoveries of elements from SRM 2710 (Montana soil) and SRM 2782 (Industrial sludge) were highly comparable to leach recoveries certified by the National Institute of Standards and Technology (NIST).