Advantages and effects of nitrogen doping into the central channel of plasma in axially viewed-inductively coupled plasma optical emission spectrometry

The effects and benefits of N₂ addition to the central channel of the ICP through the nebulizer gas used in ICP OES with axial view configuration were investigated in the present study. The N₂ flow rate, nebulizer gas flow rate, RF power and sample uptake rate were evaluated and compared for two sample introduction systems (pneumatic nebulization/aerosol desolvation and conventional pneumatic nebulization). It was observed that N₂ did not affect solution nebulization and aerosol transport but affects the ICP characteristics. The higher thermal conductivity of N₂ (in comparison with Ar) changes energy distribution in the ICP, observed by monitoring the signals of Ar emission lines and sodium emission. The ratio Mg(II)-280.270 nm/Mg(I)-285.213 nm was utilized as a diagnostic tool for plasma robustness. The addition of N₂ (20 mL min⁻¹) increased plasma robustness significantly and mitigated effects caused by Na, K and Ca. For 40 spectral lines evaluated, it was observed that the emission signals of ionic spectral lines were in general more affected by N₂ than those of atomic spectral lines. Detection limits, precision, sensitivity and linearity of calibration curves obtained using N₂-Ar-ICP were almost similar to those obtained using Ar-ICP. The analysis of 5 different reference materials revealed that accuracy was not degraded by adding N₂ to the Ar-ICP.     

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).     

Study of ionic-to-atomic line intensity ratios for two axial viewing-based inductively coupled plasma atomic emission spectrometers

Using two axially-viewed inductively coupled plasma (ICP) systems that exhibited different behaviors to matrix effects, the sensitivity of the Mg II 280.270 nm/ Mg I 285.213 nm line intensity ratio to the ICP operating conditions and to matrix effects was compared to that observed for alternative ionic-to-atomic line intensity ratios such as the Cd II 226.502 nm/Cd I 228.802 nm, Cr II 267.716 nm/Cr I 357.868 nm, Ni II 231.604 nm/Ni I 232.138 nm, Pb II 220.353 nm/Pb I 217.000 nm, and Zn II 206.200 nm/Zn I 213.857 nm ratios. Both robust and non-robust conditions were used. Some lines behaved differently, in particular the Mg I and Cr I lines, not only as a function of the matrix, but also as a function of the ICP system. The Mg II/Mg I ratio was found to remain a good compromise to follow changes in plasma conditions. The use of several ionic-to-atomic line ratios confirmed that axial viewing leads to matrix effects that are particularly sensitive for atomic lines. The effects cannot be totally suppressed, even under robust conditions, and regardless of the ICP system. An alternative to minimize matrix effects was the use of a buffer such as Cs at 10 g l⁻¹.     

An ultrasound-assisted digestion method for the determination of toxic element concentrations in ash samples by inductively coupled plasma optical emission spectrometry

A method of ultrasound-assisted digestion followed by inductively coupled plasma optical emission spectrometry (ICP-OES) used for the determination of toxic element concentrations (arsenic, barium, cobalt, copper, lead, nickel, strontium, vanadium and zinc) in ash samples was developed. 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 ratios. The highest line intensity ratios were observed when a nebulizer gas flow of 0.6 L min⁻¹, auxiliary gas flow of 0.2 L min⁻¹ and plasma power of 1400 W were used for radially viewed plasma. The analysis of SRM 1633b showed that the ultrasound-assisted method developed is highly comparable with the microwave digestion method standardized by the United States Environmental Protection Agency (EPA-3052). The ultrasound-assisted digestion with a digestion solution of aqua regia and hydrofluoric acid (HF) resulted in recovery rates of over 81%. One exception is arsenic which resulted in recoveries of about 60% only; however, it could be digested with good recovery (>90%) using a digestion solution of 5 mL of water and 5 mL of aqua regia. The major advantage of the ultrasound-assisted digestion over microwave digestion is the high treatment rate (30 samples simultaneously with a sonication time of 18 min).     

Use of magnesium as a test element for inductively coupled plasma atomic emission spectrometry diagnostics

To optimize the atomization and ionization processes in an inductively coupled plasma used as a source in atomic emission spectrometry, the Mg II 280.270-nm/Mg I 285.213-nm line intensity ratio is used. A theoretical ratio is calculated assuming a local thermodynamic equilibrium. A review of previously published experimental values of the ratio is given as a function of the parameters influencing the energy transfer between the plasma and the injected species. In particular, the effects of the power, the carrier gas flow-rate, the i.d. of the torch injector, the use of a sheathing gas and the presence of hydrogen are described. Values of the ratio close to the theoretical values are obtained with the use of a high power (> 1.4 kW), a low carrie gas flow-rate (< 0.6 1 min^?1 and a large i.d. of the injector (> 2 mm). This optimization can also be applied to the minimization of interference effects due to the presence of sodium.     

Combination of the ionic-to-atomic line intensity ratios from two test elements for the diagnostic of plasma temperature and electron number density in Inductively Coupled Plasma Atomic Emission Spectroscopy

In Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) spectrochemical analysis, the MgII(280.270 nm)/MgI(285.213 nm) ionic to atomic line intensity ratio is commonly used as a monitor of the robustness of operating conditions. This approach is based on the univocal relationship existing between intensity ratio and plasma temperature, for a pure argon atmospheric ICP in thermodynamic equilibrium. In a multi-elemental plasma in the lower temperature range, the measurement of the intensity ratio may not be sufficient to characterize temperature and electron density. In such a range, the correct relationship between intensity ratio and plasma temperature can be calculated only when the complete plasma composition is known. We propose the combination of the line intensity ratios of two test elements (double ratio) as an effective diagnostic tool for a multi-elemental low temperature LTE plasma of unknown composition. In particular, the variation of the double ratio allows us discriminating changes in the plasma temperature from changes in the electron density. Thus, the effects on plasma excitation and ionization possibly caused by introduction of different samples and matrices in non-robust conditions can be more accurately interpreted. The method is illustrated by the measurement of plasma temperature and electron density in a specific analytic case.     

Mixed-gas inductively coupled plasma atomic emission spectrometry using a direct injection high efficiency nebulizer

Experimental studies and computer simulations were conducted to identify plasma operating conditions and to explore and contrast the excitation conditions of Ar, Ar-O2, and Ar-He inductively coupled plasmas (ICPs) for the introduction of microliter volumes of sample solutions with a direct injection high efficiency nebulizer (DIHEN). The best MgII 280.270 nm/MgI 285.213 nm ratio (6.6) measured with Ar ICP atomic emission spectrometry for the DIHEN (RF power = 1500 W; nebulizer gas flow rate = 0.12 L min(-1)) was less than the ratio (8.2) acquired on the same instrument for conventional nebulization (1500 W and 0.6 L min(-1)). Addition of small amounts of O2 or He (5%) to the outer gas flow improved excitation conditions in the ICP, that is, a more robust condition (a MgII/MgI ratio of up to 8.9) could be obtained by using the DIHEN with Ar-O2 and Ar-He mixed-gas plasmas, thereby minimizing some potential spectroscopic and matrix interferences, in comparison to Ar ICPAES.     

Compensation of Ca and Na Interference Effects in Axially and Radially Viewed Inductively Coupled Plasmas

The linear relationship between Ca and Na interferences and energy potentials for a wide range of atomic and ionic lines is used to compensate for variable intensity suppression in robust axially and radially viewed inductively coupled plasmas (ICPs). In the axial configuration, intensity attenuation varied from 0 to 40% in the presence of 0.5% Ca and Na. In the radially viewed ICP, interferences were smaller, varying from 5 to 15% for 0.5% Na and from 10 to 30% for 0.5% Ca. Signal attenuation was broadly a linear function of the energies of the spectral lines. These linear functions were estimated by using spectral lines covering the energy range from Sb I 206.833 (5.98 eV), Y II 371.209 and Sc II 361.384 (9.9 eV), Sc II 255.237 (11.42 eV), and Be II 313.042 (13.28 eV) nm. These functions were then used as variable internal standards to compensate for Ca, Na, and mixed Ca–Na matrix effects. Whereas analyte recoveries without compensation varied from about 40 to 90%, they varied mostly from 100 ± 5% when these functions were used. In the presence of Ca and Na, the Mg II 280.270/Mg I 285.213 nm intensity ratio decreased from about 12 for an aqueous solution to 9 at 1.5 kW. Such values confirm that the radially and axially viewed ICPs were robust.     

Determination of mineral and trace element concentrations in pine needles by ICP-OES: evaluation of different sample pre-treatment methods

In the present study, the determination of mineral and trace elements (Al, B, Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn) from pine needles using three sample pre-treatment methods followed by inductively coupled plasma optical emission spectrometry, was examined. Sample pre-treatment methods tested were microwave digestion, ultrasound-assisted digestion and dry ashing. The new ultrasound-assisted digestion method was optimised by the analysis of the standard reference material (SRM) 1575a (pine needles) sample. The speed of dry ashing method was significantly increased by ultrasound dissolution after ashing. All the ICP-OES 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 ratios. The microwave digestion resulted generally in slightly higher element concentrations than ultrasound-assisted digestion. B, Cu and Na resulted in such low concentrations that they could not be accurately determined by using the microwave digestion method. The t-tests found no significant differences between the certified and the determined element concentrations of the SRM 1575a using the dry ashing method followed with ultrasound dissolution.     

Inductively-coupled plasma/atomic emission spectrometry of sulfur with a vacuum scanning spectrometer and its application to the analysis of coal liquefaction catalysts

Inductively-coupled plasma/atomic emission spectrometry with a high-resolution vacuum scanning monochromator is described for the determination of sulfur at 180.734 nm. The behavior of the signal-to-background ratio is investigated as functions of RF power, argon gas flow rate and observation height above the load coil. Under the operating conditions selected, the detection limit is 3 μg l^?1. The Se I 196.090-nm line is chosen as internal standard, because the S/Se line pair exhibited the least change with carrier gas flow rate and acid concentration of solution. Sulfur in NiMo and CoMo/ Al₂O₃ catalysts used for coal liquefaction is determined as S(II) and S(VI) species. The total amount of the species agreed well with the sulfur value obtained by the conventinal combustion method.     

Flow injection on-line preconcentration with an ion-exchange resin coupled with microwave plasma torch-atomic emission spectrometry for the determination of trace rare earth elements

A sensitive and rapid on-line method has been developed for the determination of trace amounts rare earth elements (REEs), lanthanum, cerium, neodymium and yttrium, by microwave plasma torch-atomic emission spectrometry (MPT-AES) combined with micro-column separation/preconcentration. A strong basic cinnamene anion exchange resin is used for matrix elimination and enrichment of the analytes. The adsorbed metal ions are subsequently eluted from the column and transferred into the detector with nitric acid solution for simultaneous multi-element determination. Various factors influencing the separation/preconcentration, sample flow rate, loading time, acidity and eluent flow rate, concentration, have been studied in detail. Under the optimized conditions, the detection limits for lanthanum, cerium, neodymium and yttrium based on three times of standard deviations of blank by 7 replicates are 0.89, 2.02, 1.56 and 0.78 μg·L^− 1, and the relative standard deviations are determined as 1.54, 4.29, 4.95 and 3.90%, respectively. The proposed method has been applied to the analysis of the four REEs in high purity Sm₂O₃, Eu₂O₃, Gd₂O₃, Tb₂O₃, Dy₂O₃, Yb₂O₃, and Lu₂O₃ samples with a recovery range of 95.1-104.8%.     

Effect of rare earth oxides on the thermal decomposition of barium oxalate

Catalytic activity of rare earth oxides (REO); La₂O₃, Sm₂O₃, Gd₂O₃ and Ce₂O₃ on the isothermal decomposition of barium oxalate has been studied at 723 K. The α?t plots for pure salt as well as mixtures indicate that the process follows: initial gas evolution, a short acceleratory and a long decay stages. The results of the kinetic analysis show that Prout-Tompkins relationship and two-dimensional phase boundary reaction give best fit of the data for both pure salt as well as mixtures. The rate constants of acceleratory and decay periods are enhanced remarkably by adding REO admixtures and their catalytical activity is in the order La₂O₃>Sm₂O₃>Gd₂O₃ >Ce₂O₃. The plausible mechanism of decomposition and the role of admixture there on has been discussed in the light of electron transfer process.     

A synthesis strategy for various pseudo-vaterite LnBO3 nanosheets via oxides-hydrothermal route

A series of pseudo-vaterite lanthanide orthoborates LnBO₃ (Ln = Sm, Gd, Dy, Er and Y) nanosheets are firstly prepared via an oxides-hydrothermal process, in which rare earth oxide Ln₂O₃ and H₃BO₃ in stoichiometric are directly used as precursors. Some rare earth borates nanosheets are facilely obtained with thickness ca. 50 nm and sizes in region of 1–10 μm. However, pure ErBO₃ and YBO₃ nanomaterials cannot be obtained unless EDTA is added into the reaction system. Ion radius is a critical influencing factor on the growth of the nanocrystals. Meanwhile, it is found the crystal growth can be modified by ions doped process. A possible growth mechanism of the pseudo-vaterite LnBO₃ is discussed.     

Investigation of four digestion procedures for multi-element determination of toxic and nutrient elements in legumes by inductively coupled plasma-optical emission spectrometry

A simple and reliable multi-element procedure for determination of essential (Cr, Cu, Fe, Mg, Mn, Zn) and toxic (Al, Cd, Pb) elements in legumes by inductively coupled plasma-optical emission spectrometry (ICP-OES) was developed. In this contribution, four different digestion procedures were thoroughly investigated and accurately evaluated with respect to their affect on the analysis of legumes. These included wet digestion with HNO₃/H₂SO₄ and HNO₃/H₂SO₄/H₂O₂, and dry ashing with Mg(NO₃)₂ and Mg(NO₃)₂/HNO₃. Two calibrations (aqueous standard and standard addition) procedures were studied, and proved that standard addition was preferable for all analytes. ICP-OES operating parameters, such as radio-frequency (RF) incident power, sample uptake flow rate and nebulizer argon gas flow rate were optimized. The precision as repeatability, expressed as relative standard deviation (R.S.D.) for aqueous standard containing 250 μg l⁻¹ of each analyte was in the range1.5-8.0%. The accuracy, expressed as relative error was generally varied in the range of 0.5-10% for all analytes, while the quantification limits were lower than 2.5 μg g⁻¹. Although, acceptable results were obtained from all developed procedures, wet digestion method with HNO₃/H₂SO₄/H₂O₂ is recommended for better recovery. The good agreement between measured and certified concentrations with respect to IAEA-331 and IAEA-359 (CRM's supplied by IAEA, International Atomic Energy Agency) indicates that the developed analytical method is well suited for determination of toxic and nutrient elements in legumes and possibly similar matrices.     

Some aspects of matrix effects caused by sodiumtetraborate in the analysis of rare earth minerals with the aid of inductively coupled plasma atomic emission spectroscopy

When inductively coupled plasma atomic emission spectroscopy (ICP-AES) is applied to the analysis of rare earth (RE) minerals, it is necessary to use a flux, for instance Na₂B₄O₇, for the decomposition of samples. Some aspects of the matrix effect caused by large amounts of Na₂B₄O₇ in the analyte solutions are studied in this work. First, it is shown that this matrix effect is lowered by a factor of two when selecting the aerosol-carrier gas flow giving maximum net line intensity instead of the one giving a maximum intensity ratio of fine-to-background. It became evident during a second series of experiments that the high concentrations of Na₂B₄O₇ lower the excitation temperature. They also cause quenching of metastable argon which certainly contributes to the observed matrix effect.     

Characterization of a microwave microstrip helium plasma with gas-phase sample introduction for the optical emission spectrometric determination of bromine,chlorine, sulfur and carbon using a miniaturized optical fiber spectrometer

Continuous flow generation of Br₂, Cl₂ and H₂S coupled to a low-power 2.45 GHz microwave microstrip He plasma exiting from a capillary gas channel in a micro-fabricated sapphire wafer with microstrip lines has been used for the optical emission spectrometric determination of Br, Cl and S using a miniaturized optical fiber CCD spectrometer. Under optimized conditions, detection limits (3σ) of 330, 190 and 220 μg l^− 1 for Br, Cl and S, respectively, under the use of the Br II 478.5 nm, Cl I 439.0 nm and S I 469.0 nm lines were obtained and the calibration curves were found to be linear over 2 orders of magnitude. In addition, when introducing CO₂ and using the rotational line of the CN molecular band at 385.7 nm the detection limit for C was 4.6 μg l^− 1. The procedure developed was found to be free from interferences from a number of metal cations and non-metal anions. Only the presence of CO₃²⁻ and CN⁻ was found to cause severe spectral interferences as strong CN and C₂ molecular bands occurred as a result of an introduction of co-generated CO₂ and HCN into the plasma. With the procedure described Br, Cl and S could be determined at a concentration level of 10–30 mg l^− 1 with accuracy and precision better than 2%.     

Vibrational spectroscopy of phthalocyanine and naphthalocyanine in sandwich-type (na)phthalocyaninato and porphyrinato rare earth complexes. Part 15: The IR characteristics of phthalocyanine in homoleptic tetrakis(phthalocyaninato) rare earth(III)-cadmium(II) quadruple-deckers

The infra-red (IR) spectroscopic data for a series of twelve sandwich-type homoleptic tetrakis[2,3,9,10,16,17,23,24-octa(octyloxy)phthalocyaninato] rare earth(III)-cadmium(II) quadruple-decker complexes [Pc(OC₈H₁₇)₈]M[Pc(OC₈H₁₇)₈]Cd[Pc(OC₈H₁₇)₈]M[Pc(OC₈H₁₇)₈] (M = Y, Pr–Yb except Pm) have been collected with resolution of 2 cm⁻¹ and their interpretation in terms tried by analogy with the IR characteristics of bis(phthalocyaninato) cerium double-decker [Pc(OC₈H₁₇)₈]Ce[Pc(OC₈H₁₇)₈] in which the macrocyclic ligands exist as the phthalocyanine dianion. Similar to the bis/tris(phthalocyaninato) rare earth sandwich counterparts, all the absorptions contributed primarily by or at least containing contribution from the vibrations of pyrrole or isoindole stretching, breathing or deformation or aza stretching in the IR spectra of these quadruple-decker compounds show dependent nature on the rare earth ionic size. The shift toward higher energy direction in the frequencies of these vibrations along with the decrease of the rare earth radii reveals the effective and increasing π–π interactions in these quadruple-decker sandwich compounds in the same order. Nevertheless, the decreased sensitivity of the frequencies of the above mentioned vibration modes in particular the weak absorption band due to the isoindole stretching at 1414–1416 cm⁻¹ for the quadruple-decker on rare earth metal size in comparison with corresponding band for bis(phthalocyaninato) rare earth counterparts indicates the relatively weaker π–π interaction in these quadruple-deckers than in the double-deckers.     

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.     

Comparison in the analytical performance between krypton and argon glow discharge plasmas as the excitation source for atomic emission spectrometry

The emission characteristics of ionic lines of nickel, cobalt, and vanadium were investigated when argon or krypton was employed as the plasma gas in glow discharge optical emission spectrometry. A dc Grimm-style lamp was employed as the excitation source. Detection limits of the ionic lines in each iron-matrix alloy sample were compared between the krypton and the argon plasmas. Particular intense ionic lines were observed in the emission spectra as a function of the discharge gas (krypton or argon), such as the Co II 258.033 nm for krypton and the Co II 231.707 nm for argon. The explanation for this is that collisions with the plasma gases dominantly populate particular excited levels of cobalt ion, which can receive the internal energy from each gas ion selectively, for example, the 3d⁷4p ³G₅ (6.0201 eV) for krypton and the 3d⁷4p ³G₄ (8.0779 eV) for argon. In the determination of nickel as well as cobalt in iron-matrix samples, more sensitive ionic lines could be found in the krypton plasma rather than the argon plasma. Detection limits in the krypton plasma were 0.0039 mass% Ni for the Ni II 230.299-nm line and 0.002 mass% Co for the Co II 258.033-nm line. However, in the determination of vanadium, the argon plasma had better analytical performance, giving a detection limit of 0.0023 mass% V for the V II 309.310-nm line.     

Synthesis and magnetic properties of ALnO2 (A=Cu or Ag; Ln=rare earths) with the delafossite structure

Synthesis, structures, and magnetic properties of ternary rare earth oxides ALnO₂ (A=Cu or Ag; Ln=rare earths) have been investigated. CuLnO₂ (Ln=La, Pr, Nd, Sm, Eu) were synthesized by the direct solid state reaction of Cu₂O and Ln₂O₃, and AgLnO₂ (Ln=Tm, Yb, Lu) were obtained by the cation-exchange reaction of NaLnO₂ and AgNO₃ in a KNO₃ flux. These compounds crystallized in the delafossite-type structure with the rhombohedral 3R type (space group: R-3m). Magnetic susceptibility measurements showed that these compounds are paramagnetic down to 1.8 K. Specific heat measurements down to 0.4 K indicated that CuNdO₂ ordered antiferromagnetically at 0.8 K.