A novel bottom-viewed inductively coupled plasma-atomic emission spectrometry

A novel optical configuration for inductively coupled plasma (ICP)-atomic emission spectrometry is presented. Plasma emission is measured axially via the bottom end of the ICP torch. Analytical performance, such as increase in signal-to-background ratio (SBR) over radially viewed ICP and linear dynamic range, is comparable to that of end-on axially viewed ICP reported in the literatures. Under typical ICP operating conditions (forward power=1.0–1.6 kW, central channel gas flow rate=0.8–1.4 l/min), SBR is generally five times or more that of radial-viewing mode (observation heights=3–20 mm) for atomic lines of elements of low to medium ionization potential (Na, K, Sr and Ba). The enhancement factor in SBR is two to four times for ionic lines (e.g. MgII) and atomic lines of elements of high ionization potential (Zn). The influence of ICP forward power and carrier gas flow rate on analyte emission intensity and SBR were also studied. Similar to radially viewed ICP, as forward power increases, the net emission intensity increases and SBR decreases. Using a constant flux of analyte aerosols, the net intensity decreases as the central channel gas flow rate increases. No trend of SBR vs. central channel gas flow rate, however, is found. The linear dynamic range starts and ends at analyte concentration 0.5–1 order of magnitude lower than the corresponding radial-viewing mode. As a result, the span of linear dynamic range is similar for all viewing modes. Matrix effects of K and Ca on atomic lines are different from those reported for end-on axially viewed ICPs, probably due to the difference in the plasma regions that were probed. The matrix effects on ionic lines, however, are similar in magnitude.     

新型固态检测器端视ICP-AES中Ca、Mg基体效应的研究

本文详细研究了0．1％Ca和0．1％Mg基体在端视ICP中对激发电位不同的谱线的干扰效应;对端视与侧视ICP中的基体干扰进行了比较;探讨了主要工作参数对基体干扰的影响。结果表明,在Ca、Mg基体存在时,大部分待测元素的谱线受到抑制,并且激发电位较高的谱线受抑制程度较大;侧视ICP中基体干扰比端视ICP中略好;适当增大功率和选择合适的载气流量可减少Ca或Mg基体的干扰。     

Influence of the operating conditions and of the optical transition on non-spectral matrix effects in inductively coupled plasma-atomic emission spectrometry

In order to study in ICP-AES, the influence of the plasma operating conditions, power and carrier gas flow rate, and of the optical transition on non-spectral matrix interferences, line-rich elements such as Mn, Cr and Cu have been selected. Selection of a large pool of lines was possible because of the use of multichannel solid-state detection. An axially viewed plasma was used. Matrices were K, Na, Li, Ca and Mg. Matrix effect was evaluated by comparing the signals for test elements in water. Use of robust conditions led to an almost flat response, while non-robust conditions led to a significant scattering of the signal changes. In the case of Mn, the z⁷P Mn multiplet was exemplified as it contains not only the most Mn sensitive line, the Mn II 257.610 nm resonance line, but also the 259.372 and 260.568 nm resonance lines, and the non-resonant Mn II 343.897 nm line. Even under robust conditions, the non-resonant line exhibited a different behavior. The difference with the other resonance lines was reduced by using an axially viewed ICP with a large injector id, or suppressed by using a radially viewed ICP. In the case of Cr, the z⁶D Cr II multiplet was selected as it contains three resonant lines linked to the a⁶S fundamental, and other non-resonant lines. The behavior was identical under robust conditions, while an abnormal behavior was observed for the Cr II 334.78 nm line under non-robust conditions, depending on the extent of these non-robust conditions. Cu was an interesting element as ionic lines lie in the energy sum range 15.96–16.26 eV, i.e. slightly above the Ar ionization energy. It was shown that, under robust conditions, the line behavior was not similar although the energy range was small. Moreover, this behavior was depending on the ICP system used for the experiment. It was concluded that not only the magnitude of matrix effects depends on the operating conditions but also may depend on the optical transition, illustrating the complexity of these effects.     

Evaluation of inductively coupled plasma optical emission spectrometers with axially and radially viewed configurations

The analytical performance of two inductively coupled plasma optical emission spectrometers with axially and radially viewed configurations, equipped with charge coupled device solid-state detectors was evaluated using Ar, Ba, Mg, and Ni as test elements. Both instruments have similar Echelle optical arrangements and radio-frequency generators, differing only in the viewing mode and in the diameter of the central injector tube, i.e. 2.3 for the axially and 1.4 mm for the radially viewed ICP. The figures of merit evaluated were: warm-up time, short- and long-term stabilities, UV and VIS spectral resolution and limit of detection (LOD) for Ni in 0.14 mol l⁻¹ HNO₃ and 1000 mg l⁻¹ Cr media, respectively. The influence of residual carbon content on background equivalent concentration (BEC) and sensitivity attained for Al, As, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Se and Zn was also investigated in both viewing modes. The robustness, short- and long-term stabilities, and UV and VIS spectral resolutions were similar for both configurations. For the radially viewed equipment, the warm-up time was at least a factor of 2 shorter than that for the axially viewed configuration. On the other hand, the sensitivity attained for Ni with the axially viewed arrangement was approximately 20 times better than that with the radially viewed. In both viewing modes, and for most of the evaluated elements, the values of BEC and LOD were similar for all studied carbon concentrations (from 10 to 10 000 mg l⁻¹ C) when working with robust plasma conditions. The Mg II/Mg I ratio at an applied power of 1.3 kW and a nebulizer gas flow-rate of 0.90 and 0.70 l min⁻¹ for axially and radially viewed configurations were 10.6 and 13.7, respectively. Quantitative determinations were successfully performed using both systems.     

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).     

Application of inductively-coupled plasma atomic emission spectrometry with an internal reference to the determination of sulfate and calcium in waters and brines

A method is described for the determination of sulfate and calcium in waters and brines; an inductively-coupled plasma is used with a multichannel vacuum spectrometer. Study of the behavior of the line-to-background intensity ratios for the S I 180.734, Ca II 317.933, Sc I 402.04 and Sc II 361.384-nm lines as functions of the observation height, aerosol carrier gas, power, and concentration of an easily ionized element shows that Sc II 361.384 nm can be used as an internal reference for sulfur and calcium. In the presence of high salt concentrations, the efficiency and quality of nebulization are degraded and at high aerosol gas flows in the presence of sodium, the line-to-background ratios for the ion lines are depressed and those of the atom lines are enhanced. However, under compromise conditions, the S I 180.734-nm and Ca II 317.933-nm lines exhibit significant freedom from interference caused by an easily ionized element. With the Sc II 361.384-nm line used as the internal reference, short-term precision is improved by a factor of 1.5–4, and long-term precision is improved by a factor of 2, producing data for sulfate and calcium that compare favorably with those obtained by gravimetry, titrimetry, and atomic absorption spectrometry. A detection limit of 70 μg l^?1 and a linear dynamic range of 1 g l^?1 were obtained for sulfate.     

A practical approach to non-spectral interferences elimination in inductively coupled plasma optical emission spectrometry

Matrix effects and practical possibilities of reducing accompanying non-spectral interferences in inductively coupled plasma optical emission spectrometry (ICP-OES) were studied for microconcentric Micromist, concentric and V-groove nebulizers (VGN) coupled with two cyclonic spray chambers of different sizes. The effect of a wide scale of interferents and mixtures thereof in the concentration range of up to 2 mass % (Na, Ca, Ba, La, urea) or up to 20 vol. % (nitric acid) on the analysis of Cd, Cu, K, Mg, Mn, Pb and Zn was investigated in terms of their analytical recovery and Mg(II) 280.27 nm/Mg(I) 285.29 nm line intensity ratio. Recoveries of ionic lines were lower than those of atomic lines (37–102 %) depending on the matrix concentration. The Mg(II)/Mg(I) ratios were found to be 12–15 and they slightly decreased as the matrix load increased. Exceptional behavior of pure La matrix, steeply lowering the recoveries and Mg(II)/Mg(I) ratios was observed. A Micromist nebulizer coupled with a small inner volume spray chamber provided the highest recoveries (94–102 %), lowest matrix effects across the matrix loads and, compared to others, the least significant dependence without worsening of the analytical characteristics (recoveries, signal background ratios and the Mg(II)/Mg(I) ratios) across the studied matrices.     

The determination of carbon and hydrogen in organic compounds containing metals and metalloids

The determination of carbon and hydrogen in organometallic compounds is described. Cobalto-cobaltic oxide is used as the catalytic tube filling in a rapid procedure. Compounds containing Na, K. Cu, Be, Mg, Ca. Zn, Cd, Hg, Al, B, Ga, Ti, Pb, Nb. P, As, Bi, Mo. U, Sc, Te, Mn, Fe, Co, Ni were examined; interferences were overcome where necessary and tungstic oxide proved a valuable auxiliary reagent.     

电感耦合等离子体原子发射光谱分析中易电离元素的基体干扰及其抑制的研究

选取铝、铜、镁、钙、铁、锰和锌等7种元素的9条谱线,研究电感耦合等离子体原子发射光谱法对其测定时易电离元素钾、钠的基体干扰。结果表明:易电离元素对待测元素具有较明显的干扰作用,而增大射频发射功率及降低雾化器压力可有效地抑制易电离元素对待测元素的干扰。     

Determination of major, minor and trace elements in cobalt-substituted lithium nickelate ceramic powders by inductively coupled plasma optical emission spectrometry

An analytical method was developed for the determination of three major (Li, Ni and Co) and fourteen minor or trace elements (Al, Ba, Ca, Cu, Cr, Fe, K, Mg, Mn, Na, Si, Sr, Ti and V) in LiNi_1−x Co _x O₂ (x = 0.2–0.8) ceramic powders by inductively coupled plasma optical emission spectrometry. Sample dissolution was achieved by 25% nitric acid digestion in a microwave oven. For each element, an analytical line free from spectral interferences was selected. A detailed study of matrix effects over a wide interval of total excitation energy (TEE) lines (1.62–16.50 eV) was performed at near-robust plasma conditions. A remarkable enhancement in atomic lines with TEE <4 eV was noticed, whereas a significant reduction in atomic and ionic lines with TEE >4 eV was observed. The extrapolation to infinite dilution method was successfully used to overcome these nonspectroscopic interferences. Detection limits (3σ) varied from 0.21 mg kg⁻¹ for Sr to 49.7 mg kg⁻¹ for Na. The precision of determination (obtained as the relative standard deviation) was lower than 1% for the major elements Li, Ni and Co and between 0.69 and 10% for minor and trace elements. The accuracy of the method ranged from 91 to 101% for major elements, and from 90 to 110%, or close to this range, for most of the impurities in both of the samples studied.      

Diagnostics in an air inductively coupled plasma

Radial temperature distributions in an air inductively coupled plasma discharge, operated at atmospheric pressure, are calculated from measurements of the absolute intensities of two atomic nitrogen lines (746.9 and 493.5 nm), the first negative band system of the nitrogen molecular ion at 391.4 nm, and the air continuum at 560.0 nm. The radial intensity distribution of the Mg I 285.2 and Mg II 279.6 nm lines are employed with the determined radial temperature distribution to calculate the radial electron number density throughout the normal analytical zone. The temperatures ranged from about 6000 to 10,000 K, and the electron number density varied from 5 × 10¹³ to 2 × 10¹⁶ cm^?3 in the regions above the induction coil where differences of less than 3 fold were observed between experimental and calculated Ca II to Ca I intensity ratios. On the basis of agreement among the measured temperatures and calcium ion-to-atom intensity ratios, the extent of local thermodynamic equilibrium is evaluated.     

Separation of copper(II) from uranium(VI) and many other elements by cation-exchange chromatography in acetone-hydrobromic acid media: Improved selective separation of copper

Co(II), Ni(II), Mn(II), Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, Ti(IV), V(IV), Zr, Hf, Th, Al, Sc, Y, La, the lanthanides and also U(VI), which accompany copper(II) in hydrochloric acid-acetone mixtures, can be separated from copper by eluting copper(II) with 0.50 M hydrobromic acid in 85% acetone from a column of AG 50W-X8 resin, 200–400 mesh, while all these elements are retained by the column quantitatively. Separations are sharp and quantitative, as is demonstrated by results for some synthetic mixtures. Some relevant elution curves are presented.     

The determination of I, P, B, S, As and Sn by inductively coupled plasma emission spectroscopy using lines at vacuum ultra-violet wavelengths

The application of ICP atomic emission spectroscopy (ICP-AES) for the quantitative determination of I, P, B, S, As and Sn with the aid of their lines between 170 and 200 nm is described. The spectrometer used was kept under vacuum at a pressure below 0.1 Pa and the optical path was purged with Ar gas (99.99% pure) at a flow rate of 3.5 l min⁻¹. The analytical method investigated was applied to the determination of the stated elements in iron and steel and in sea water. No spectral interferences from the close lines of the various concomitants were observed, nor matrix effects from Fe or K, Na, Mg and Ca at the concentration levels found in steel samples or sea water.     

Application of prominent spectral lines in the 125-180 nm range for inductively coupled plasma optical emission spectrometry

A new axially viewed ICP optical emission spectrometer featuring an argon-filled optic and CCD detectors was evaluated for the application of prominent spectral lines in the 125-180 nm range. This wavelength range was investigated for several analytical applications of inductively coupled plasma optical emission spectrometry (ICP-OES). There are different advantages for the application of spectral lines below 180 nm. A number of elements, such as Al, Br, Cl, Ga, Ge, I, In, N, P, Pb, Pt, S and Te, were found to have the most intense spectral lines in the wavelength range from 125-180 nm. Compared with lines above 180 nm higher signal-to-background ratios were found. Low limits of detection using pneumatic nebulization of aqueous solutions for sample introduction were calculated for Al II 167.080 nm (0.04 microg L(-1)), Br I 154.065 nm (9 microg L(-1)), Cl I 134.724 nm (19 microg L(-1)), Ga II 141.444 nm (0.8 microg L(-1)), Ge II 164.919 nm (1.3 microg L(-1)), II 142.549 nm (13 microg L(-1)), In II 158.583 nm (0.2 microg L(-1)), P I 177.500 nm (0.9 microg L(-1)), Pb II 168.215 nm (1.5 microg L(-1)), Pt II 177.709 nm (2.6 microg L(-1)), S I 180.731 nm (1.9 microg L(-1)) and Te I 170.00 nm (4.6 microg L(-1)). Numerous application examples for the use of those lines and other important spectral lines below 180 nm are given. Because of fewer emission lines from transition elements, such as Fe, Co, Cr, lines below 180 nm often offer freedom from spectral interferences. Additional lines of lower intensity for the determination of higher elemental concentrations are also available in the vacuum ultraviolet spectral range. This is specially useful when the concentrations are not in the linear range of calibration curves obtained with commonly used lines.     

Use of factorial design for evaluation of plasma conditions and comparison of two liquid sample introduction systems for an axially viewed inductively coupled plasma optical emission spectrometer

A factorial design was applied to evaluate plasma conditions employing the Mg II 280/Mg I 285 nm intensity ratio in an axially viewed inductively coupled plasma optical emission spectrometer using different sample introduction devices: a concentric or a V-groove nebulizer and a cyclonic or a Sturman-Masters spray chamber. Effects of nebulizer gas flow-rate on Mg II/Mg I ratio were different in each introduction system. Robust conditions were obtained at low nebulizer gas flow-rate when using concentric nebulizer with a cyclonic spray chamber or a concentric nebulizer and a Sturman-Masters spray chamber. However, when using a V-groove nebulizer with a Sturman-Masters spray chamber, Mg II/Mg I ratio increased at high nebulizer gas flow-rates. Recovery experiments for a milk standard reference material diluted in water-soluble tertiary amines in both robust and non-robust conditions indicated that the robust condition was reached at higher nebulizer gas flow-rates and led to better accuracy and precision when using a V-groove nebulizer.     

The determination of chromium, copper and nickel in groundwater using axial plasma inductively coupled plasma atomic emission spectrometry and proportional correction matrix effect reduction

The performance of a proportional correction matrix effect reduction procedure was investigated for an axially viewed inductively coupled plasma. It was shown that the proportional correction factor (ratio of analyte matrix effect and internal standard matrix effect) was sufficiently stable over the investigated matrix element concentration ranges (0–2000 mg/L of Na and 0–400 mg/L of Ca) for the procedure to be successful. Proportional correction results in the best correction for matrix effects compared to the classical 1?:?1 intensity ratio correction procedure or the approach without any correction, as was shown in recovery experiments using analyte spiked groundwater samples. Matrix effects as high as 18% without correction were reduced to less than 4% applying proportional correction.     

Determination of trace elements of some Egyptian crops by instrumental neutron activation,inductively coupled plasma-atomic emission spectrometric and flameless atomic absorption spectrophotometric analysis

Instrumental neutron activation analysis was used for the determination of Al, Br, Ca, Ce, Cl, Co, Cr, Cs, Eu, Fe, K, La, Mg, Mn, Na, Rb, Sb, Sc, Se, Ti, Th, V and Zn, ICP-AES for the determination Al, Ag, Ba, Be, Ca, Co, Cr, Cu, Fe, Ga, K, Li, Mg, Mn, Na, Ni, P, Sc, Sr, Ti, V and Zn and flameless AAS for the determination of Cd, Hg and Pb in egg plant, potatoes, green pepper (Leguminosae), vegetable marrow (Cucurbitaceae), pears, apple (Rosaceae), castor oil plant (Euphorbiaceae), lettuce (compositae), dill, parsley, coriander (Umbelliferae), and in some soil samples collected from Aswan province.     

Some spatial effects observed in the axially viewed filament argon microwave induced plasma with solution nebulization

Spatial profiles of analyte emission in an axially viewed argon filament microwave induced plasma sustained in the TE₁₀₁ rectangular cavity have been measured along a discharge tube cross-section for neutral atoms as well as ion lines of several elements. The filament diameter was approximately 1 mm. The analyte solution was introduced by means of an ultrasonic nebulizer without desolvation. The radial emission distribution depends on the operating parameters and is different for each of the analytes examined. Spatial distributions of excitation temperature (4000–6000 K) measured with Ar I lines by the Boltzmann plot method as well as electron temperature (6000–8000 K) by line to continuum emission ratio measurements at Ar I 430 nm and electron number density (1–1.5×10¹⁵ cm⁻³) by the Stark broadening method of the H_β line were determined to support the evidence of plasma processes. In the presence of excess sodium the enhancement of emission intensity and its shift to the plasma center appears to be the result of increased analyte penetration to the plasma. Changes in spatial emission profiles for Ca atoms and ions suggest that for this element ambipolar diffusion may be important as an additional interference mechanism. A possibility of minimizing spectral interferences from argon emission lines by choosing an off-axis plasma region for emission intensity measurements is indicated.     

Metal-substituted Ti8C12 metallocarbohedrynes: toward less reactive clusters as building blocks of cluster-assembled materials

To form cluster-assembled materials, the clusters should have low reactivity and be characterized by a closed-shell electronic configuration with a large gap between the highest occupied and the lowest unoccupied molecular orbitals (HOMO-LUMO). Using spin-polarized density functional theory calculations, we investigate the M-substituted Ti(8)C(12) metallocarbohedrynes to search for less reactive clusters as building blocks for cluster-assembled materials (M = Be, Mg, Ca, Sr, Ba and Sc, Y). The selected atoms in the correct stoichiometry would produce a metallocarbohedryne that is isoelectronic with the Ti(8)C(12)(2+), which has a closed-shell electronic configuration and an enhanced HOMO-LUMO gap of 1.735 eV. According to our results, the HOMO-LUMO gaps of the M-substituted Ti(8)C(12) metallocarbohedrynes are in the range of 0.715-0.979 eV for the case of Be, Mg, Ca, Sr and Ba and in the range of 0.865-1.294 eV for the case of Sc and Y. Among all the M-substituted metallocarbohedrynes we consider here, one of the isomers of Ti(6)Sc(2)C(12) is not only energetically more favorable but also exhibits a larger HOMO-LUMO gap of 1.294 eV. This result indicates that the Ti(6)Sc(2)C(12)(4) metallocarbohedryne should be less reactive than the Ti(8)C(12) metallocarbohedryne which has a narrow HOMO-LUMO gap of 0.146 eV. Moreover, we show that the intercluster interaction between two individual Ti(6)Sc(2)C(12)(4) metallocarbohedrynes is relatively weak compared to the Ti(8)C(12) dimer.     

Determination of 21 elements by INAA for certification of SRM 1570a,Spinach

Analyses for certification have been made by instrumental neutron activation analysis (INAA) for the determination of 21 elements in the National Institute of Standards and Technology (NIST) Spinach renewal reference material, SRM 1570a. Elements determined included ones with short halflife products (Al, V, Ca, Mg), intermediate halflife products (Mn, Na, K, La), and long halflife products (Ba, Co, Cr, Cs, Eu, Fe, Rb, Sb, Sc, Se, Sr, Th, and Zn). For the first time a new robotic sample changer was used in the counting of long halflife indicator isotopes for certification of an SRM. Uncertainties obtained averaged±1.80% for the four major and minor constituents (Ca, K, Mg, Na); ±3.14% for elements with concentrations from 1 to 400 mg/kg (Al, Ba, Cr, Fe, Mn, Rb, Sr, and Zn); and±8.31% for the ultra trace elements (<1 mg/kg) (Co, Cs, Eu, La, Sb, Sc, Se, Th, and V).