A possible steady state kinetic model for the atomization and excitation processes during inductively coupled plasma atomic emission spectrometry: application to interference effects of lithium on calcium

A possible steady state kinetic model is presented for the atomization and excitation processes during inductively coupled plasma atomic emission spectrometry. The model takes into account the relative rates of (a) thermal dissociation of analyte salt, (b) recombination of counter atom and analyte atoms, (c) charge transfer between analyte and interferent species, (d) charge transfer between analyte and argon species, and (e) ion/electron collisional de-ionization. Number density ratio data, n(u)'/n(u), where n(u) denotes the excited state and the prime denotes the presence of an interferent element, are presented showing that the predictions of the model are consistent with the signal enhancement observed at low analyte concentrations when Ca is determined by ICP in the presence of excess Li.     

A possible steady state kinetic model for the atomization process during flame atomic spectrometry: Application to mutual atomization interference effects between group I elements

 A possible steady state kinetic model for the atomization process during flame atomic spectrometry is presented. It takes into account the relative rates of (a) thermal dissociation of analyte and interferant metal salts, (b) recombination of counter atom and analyte and interferant atoms, (c) charge transfer between analyte and interferant species, and (d) ion/electron collisional de-ionization. The model predicts a law of mass action type of the thermal dissociation constant in agreement with the currently accepted p-LTE theory. Expressions are derived for the analyte ground state population in the absence and presence of an interferant metal in terms of the rate constants for thermal dissociation of analyte and interferant salts, recombination of counter atom and analyte and interferant atoms, charge transfer between analyte atoms and interferant metal ions and collisional de-ionization, and α and β, the fractions of analyte ions undergoing charge transfer and collisional de-ionization, respectively. The estimation of α and β, and of the various rate constants is discussed. Data are presented showing that the predictions of the model are consistent with the observed interference effects. Received: 2 October 1995 / Received: 15 March 1996/Accepted: 23 March 1996     

A possible steady state kinetic model for the atomization process during flame atomic spectrometry: Application to atomization interference effects of aluminum on Group II elements

The atomization interference effects of AlCl₃ on MgCl₂ and CaCl₂ during flame atomic absorption spectrometry were studied in terms of a steady state kinetic model which takes into account relative rates of thermal dissociation of analyte and interferant metal salts, recombination of counter atom and analyte and interferant atoms, charge transfer between analyte and interferant species, and ion/electron collisional de-ionization within the plasma. Data are presented showing that the interference of AlCl₃ on the atomization of MgCl₂ and CaCl₂ in an air-acetylene flame is due (a) to interference effects due to AlCl₃ which occur prior to complete atomization of the Group II metal chlorides, and (b) to the recombination of the Group II metal and the chlorine atom which is enhanced by the increased density of the chlorine atom as a result of the dissociation of the AlCl₃ interferant. Received: 23 February 1998 / Revised: 18 December 1998 / Accepted: 25 December 1998     

A possible steady state kinetic model for the atomization process during flame atomic spectrometry: Application to mutual atomization interference effects between group I elements

A possible steady state kinetic model for the atomization process during flame atomic spectrometry is presented. It takes into account the relative rates of (a) thermal dissociation of analyte and interferant metal salts, (b) recombination of counter atom and analyte and interferant atoms, (c) charge transfer between analyte and interferant species, and (d) ion/electron collisional de-ionization. The model predicts a law of mass action type of the thermal dissociation constant in agreement with the currently accepted p-LTE theory. Expressions are derived for the analyte ground state population in the absence and presence of an interferant metal in terms of the rate constants for thermal dissociation of analyte and interferant salts, recombination of counter atom and analyte and interferant atoms, charge transfer between analyte atoms and interferant metal ions and collisional de-ionization, and α and β, the fractions of analyte ions undergoing charge transfer and collisional de-ionization, respectively. The estimation of α and β, and of the various rate constants is discussed. Data are presented showing that the predictions of the model are consistent with the observed interference effects.     

A possible steady state kinetic model for the atomization process during flame atomic spectrometry: Application to atomization interference effects of aluminum on Group II elements

The atomization interference effects of AlCl₃ on MgCl₂ and CaCl₂ during flame atomic absorption spectrometry were studied in terms of a steady state kinetic model which takes into account relative rates of thermal dissociation of analyte and interferant metal salts, recombination of counter atom and analyte and interferant atoms, charge transfer between analyte and interferant species, and ion/electron collisional de-ionization within the plasma. Data are presented showing that the interference of AlCl₃ on the atomization of MgCl₂ and CaCl₂ in an air-acetylene flame is due (a) to interference effects due to AlCl₃ which occur prior to complete atomization of the Group II metal chlorides, and (b) to the recombination of the Group II metal and the chlorine atom which is enhanced by the increased density of the chlorine atom as a result of the dissociation of the AlCl₃ interferant.     

A helium inductively coupled plasma for atomic emission spectrometry

An annular helium inductively coupled plasma (He ICP) was generated at atmospheric pressure. No external cooling was used to stabilize the plasma. Aqueous solution was injected into the plasma without any difficulty. Preliminary results revealed that the annular He ICP was capable of exciting elements such as Cl and Br which possess high excitation energies. Atomic emission detection limits for Cl and Br were improved by factors of 63 and 34, respectively, as compared to the results obtained from the argon inductively coupled plasma. The excitation temperature of the annular He ICP (4180 K) was less than that of an Ar ICP (5570 K).     

Carbon-related matrix effects in inductively coupled plasma atomic emission spectrometry

In Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES), it has been observed that the emission intensity of some atomic lines is enhanced or depressed by the presence of carbon in the matrix. The goal of this work was to investigate the origin and magnitude of the carbon-related matrix effects in ICP-AES. To this end, the influence of the carbon concentration and source (i.e. glycerol, citric acid and potassium hydrogen phthalate), the experimental conditions and sample introduction system on the aerosol characteristics and transport, plasma excitation conditions and the emission intensity of several atomic and ionic lines of a total of 15 elements has been studied. Results indicate that carbon related matrix effects do not depend on the carbon source and they become more severe when the amount of carbon loaded into the plasma increases, i.e., when using: (i) carbon concentrations higher than 5 g L^− 1; (ii) high sample uptake rates; and (iii) efficient sample introduction systems. Thus, when introducing carbon into the plasma, the emission intensity of atomic lines with excitation energies below 6 eV is depressed (up to 15%) whereas the emission intensity of atomic lines of higher excitation energies (i.e. As and Se) are enhanced (up to 30%). The emission intensity of the ionic lines is not affected by the presence of carbon. The origin of the carbon-related interferences on the emission intensity of atomic lines is related to changes in the line excitation mechanism since the carbon containing solutions show the same aerosol characteristics and transport efficiencies as the corresponding aqueous solutions. Based on the previous findings, a calibration approach for the accurate determination of Se in a Se-enriched yeast certified material (SELM-1) has been proposed.     

电感耦合等离子体原子发射光谱法测定工业电解质中钙、镁、锂

工业电解质中微量元素钙、镁、锂对电解槽的正常运行非常重要。本文采用高氯酸加热挥发除氟,以盐酸(1 1)溶解残渣,选用Ca317.9nm、Mg297.5nm、Li670.7nm作为分析谱线,考察了样品处理方法、共存元素干扰对测定结果的影响。建立了电感耦合等离子体原子发射光谱法测定工业电解质中钙、镁、锂的方法。结果表明：不同的电解质因其所含氧化铝的不同会有部分不溶杂质,但对微量元素的测定影响很小,可以忽略不计。共存元素铝和钠不干扰微量元素的测定。按照试验方法对2个电解质标准样品进行了测定,其测定值与标准值吻合。同时对不同电解槽的工业电解质样品进行了分析,其结果的相对标准偏差(RSD,n=11)在0.69%-5.68%之间,满足生产分析的需要。     

Matrix-induced shift effects in axially viewed inductively coupled plasma atomic emission spectrometry

In order to study matrix effects and efficiency of internal standardization with an axially-viewed ICP-AES system, a large number of elements with atomic lines in the 2.9–7.8-eV excitation energy range and ionic lines in the 7.7–16.5-eV energy sum range were selected and matrix effects were evaluated using a multichannel detector having a wavelength coverage in the range 167–785 nm. Na and Ca were selected as interferent elements at a concentration of up to 10 g l⁻¹, along with nitric acid, up to a concentration of 20% (v/v). Several operating conditions were used, ranging from robust conditions (1500 W, 0.65 l min⁻¹ for the carrier gas) to non-robust conditions (800 W, 1.2 l min⁻¹). Under robust conditions, a rather flat, depressive effect was observed for ionic lines and atomic lines. This depressive effect was mainly assigned to the aerosol transport and filtering phenomena and was element or acid concentration-dependent. Within this depressive effect, some small departures from the flat effect were observed. However, these small effects exhibited the same patterns over the interferent element concentration range of 1–10 g l⁻¹, i.e. these effects were shifted as a function of the interferent concentration rather than multiplied. A consequence is that internal standardization to compensate for matrix effects on ionic lines was found to be more efficient when based on additive (i.e. shift) effects rather than on multiplicative (i.e. proportional) effects. Under non-robust conditions, signal compensation was found to be inefficient.     

Modified Babington nebulizer for inductively coupled plasma atomic emission spectrometry.

A PTFE Babingtonnebulizer equipped with a hood was investigated for inductively coupled plasma atomicemission spectrometry in conjunction with a PTFE cyclone chamber, in order to nebulize various sample solutions containing high salts, hydrofluoric acid and/or suspended solid. A hood of 3 mmphi (nozzle side) - 5 mmphi (outlet side) and 6 mm in length gave a comparable or higher sensitivity compared to a system with a commercially available concentric nebulizer and a glass cyclone chamber. Moreover, the present nebulizer was fully interchangeable with a concentric one at normal argon pressure, attaining sufficient stability, a short wash-out time and good nebulizing of high matrices solutions. The present system was successfully applied to the determination of trace impurities in highly pure silica powders.     

Application of wavelet transform to background correction in inductively coupled plasma atomic emission spectrometry

A background correction method based on wavelet transform was devised and applied to inductively coupled plasma atomic emission spectrometry (ICP-AES). The proposed approach separated background from analyte signal according to their different frequencies. Compared with the analyte signal, the background has a low frequency. By removal of the components attributed to the signal, the background over the spectral window of the analyte line can be fitted through wavelet reconstruction. The results showed that the wavelet transform technique could handle all kinds of background and low signal-to-background ratio spectra, and required no prior knowledge about the sample composition, no selection of suitable background correction points, and no mathematical assumption of the background distribution. This technique performed as well as the conventional three-point background correction method for linear backgrounds, and provided better results than the latter for curved backgrounds. The proposed procedure was illustrated, by processing real spectra, to be an effective and practical tool for background correction in ICP-AES.     

Interface for capillary electrophoresis coupled with inductively coupled plasma atomic emission spectrometry.

A modified concentric nebulizer was used as the interface to couple capillary electrophoresis (CE) to inductively coupled plasma atomic emission spectrometry (ICP-AES). The CE capillary replaces the central tube of the concentric nebulizer. The tip of the nebulizer tapers slowly to allow uncertainty in the position of the capillary. A platinum wire was inserted into the CE capillary to provide electrical connection to the CE power supply. pH changes inside the capillary due to electrolysis of the background buffer electrolyte was small and has minimal effects on the CE separation. The peak broadening effects due to the nebulizing gas flow, however, were significant. Resolution decreases quickly when the flow-rate of the carrier gas increases. Sample stacking technique was used to improve the resolution of species of opposite charge, e.g., Cr(VI) vs. Cr(III) ions. Detection limit of Cr based on peak area is approximately 10 ppb for the CE-ICP-AES system.     

Some hydride generation inter-element interference studies utilizing atomic absorption and inductively coupled plasma emission spectrometry

Three commercially available hydride generation devices have been used in conjunction with atomic absorption spectrometry and inductively coupled plasma emission spectrometry to study the possible inter-element interferences from fifty elements. Nineteen of these elements caused signal reductions of at least 10%. These interferences were reduced (drastically in some cases) by an appropriate choice of hydride generation system and by manipulation of the acid strength.     

A systematic approach to optimum working conditions with inductively coupled plasma atomic emission spectrometry

Optimum experimental factors were determined for the analytical determination of Al, Cd, Fe, Pb, and Zn by ICP atomic emission spectrometry. Based on systematically determined factor levels, working conditions were found that gave similar, and sometimes better results compared with the hitherto used levels of factors. All measurements were performed with a sampling time of 150 ms as often used in routine analysis in the laboratory. This optimization resulted in a reduced outer plasma gas flow from 15 L/min argon to 12 L/min without any relevant changes of the achievable detection limits. A serious problem was that only one analytical line of Al could be used. A comparison with the lower limit of application (comparable with the detection limit) from German directive DIN 38406, part 22 ([1]), showed that the detection limits of Al and Fe are superior, whereas for Cd there was only little improvement. The detection limits of Zn and especially Pb are always higher than the lower range of application under these conditions. Therefore, the use of two device-parameter sets for hard and soft lines, respectively, is strongly suggested. Maps with the observed signal-to-noise-ratios were systematically acquired for each element analyzed in connection with different strategies for optimum search. mon compromise condition (combined analysis) and the limits of quantification demanded in the German directive DIN 38406, part 22 [1]. Only four, but the most important, experimental factors were changed, the other experimental factors were always kept constant (Tables 1 and 2).     

A systematic approach to optimum working conditions with inductively coupled plasma atomic emission spectrometry

Optimum experimental factors were determined for the analytical determination of Al, Cd, Fe, Pb, and Zn by ICP atomic emission spectrometry. Based on systematically determined factor levels, working conditions were found that gave similiar, and sometimes better results compared with the hitherto used levels of factors. All measurements were performed with a sampling time of 150 ms as often used in routine analysis in the laboratory. This optimization resulted in a reduced outer plasma gas flow from 15 L/min argon to 12 L/min without any relevant changes of the achievable detection limits. A serious problem was that only one analytical line of Al could be used. A comparison with the lower limit of application (comparable with the detection limit) from German directive DIN 38406, part 22 ([1]), showed that the detection limits of Al and Fe are superior, whereas for Cd there was only little improvement. The detection limits of Zn and especially Pb are always higher than the lower range of application under these conditions. Therefore, the use of two device-parameter sets for hard and soft lines, respectively, is strongly suggested. Maps with the observed signal-to-noise-ratios were systematically acquired for each element analyzed in connection with different strategies for optimum search.     

Particle sample introduction system for inductively coupled plasma–atomic emission spectrometry

Development and characterization of a new, relatively inexpensive, computer-controlled, particle sample introduction (PSI) system for programmable delivery of small amounts of diluted powdered samples into an inductively coupled plasma (ICP) and measurement by atomic emission spectrometry (AES) is described. The PSI was developed for use with non-hygroscopic particles, in particular those with a particle weight in the ng range (i.e., with a diameter in low μm-range) and for solids that can be converted to a powder (i.e., a collection of particles). In this first report on PSI–ICP–AES, linearity of calibration curves and plasma loading concerns were addressed using three modes of operation. In the first mode, the PSI operated similar to a nebulizer and it delivered to the plasma for a period of 5–10 s a relatively constant amount of particles diluted with graphite. In the second mode, the PSI delivered to the plasma a small “puff” of a diluted sample, thus generating a transient, time-domain signal with duration of about a second. In the third mode, an even smaller “puff” was delivered to the plasma and, using high-speed data acquisition (in the kHz range), time-resolved emission signals from individual, μm-diameter and ng-weight particles were observed. Thus, the PSI can also be thought of as a nano-particle (i.e., ng rather than nm) sample introduction system. Similarly, the high-speed, wide-bandwidth single-channel time-resolved data acquisition mode enabled the determination of particle-size distribution. In addition, a dual-channel (or dual-element) mode enabled homogeneity studies on a per-individual-particle basis. In all modes, linear calibration curves were obtained (provided that plasma loading was avoided). Per-cent relative standard deviation ranged between 3.1% and 4.2% for Ni in certified reference materials but was as high as 50% for heterogeneous soil samples. Tungsten emission signals from refractory tungsten carbide powders were enhanced using mixed gases and by modifying the chemical environment of the ICP using SF₆. Furthermore, when coupled with high-speed data acquisition, PSI brought unique capabilities to ICP–AES for homogeneity studies from individual ng-weight particles and for the determination of particle size distributions. Overall, it was concluded that PSI is an attractive alternative to powder sample introduction systems described in the literature.     

Influence of hydrogen gas over the interference of acids in inductively coupled plasma atomic emission spectrometry

The effect of hydrogen gas on the plasma and its influence on acid interferences in plasma atomic emission spectrometry was studied. The study was performed with HCl and HNO₃ in the concentration range of 0–2 mol l⁻¹. Vanadium and magnesium were used as test elements, the study was extended to other several elements. The effects of hydrogen gas on the plasma were studied by measuring excitation temperature, electron number density and the ionic-to-atomic line intensity ratio. The net effect of hydrogen was an increase in electron density and ionic to atomic line intensity ratio. A small increase in the excitation temperature was observed. The signal suppression for ionic lines causes by mineral acid was reduced when small amounts of hydrogen was introduced into the plasma as sheathing gas. This effect was attributed to the increase in plasma electron density.     

Plasma behavior during electrothermal vaporization sample introduction in inductively coupled plasma atomic emission spectrometry

Electrothermal vaporization (ETV) sample introduction in inductively coupled plasma atomic emission spectrometry suffers from severe matrix effects. In the present study, the differences between wet and dry plasma conditions are studied. In addition, the influence of the sample composition was investigated. An inductively coupled plasma optical emission spectrometer, with detection based on charge transfer, allowed the simultaneous measurement of ionic and atomic emission line intensities during the transient signal. Mg and Cr were the test elements. The ion-to-atom line ratio increases at higher power settings, but the changes were larger when a nebulizer was used for sample introduction than with ETV sample introduction. The decrease of ion-to-atom line ratios at increasing observation height was more pronounced when ETV was used, due to the absence of water vapor. The gas flow rate showed a stronger influence for nebulization than for ETV. In the presence of a calcium matrix, lower ion-to-atom line ratios were observed, but the ratio did not change significantly within the transient emission signal. Similar line ratios were observed for different amounts of calcium matrix. The values of ion-to-atom line ratios for Mg and Cr indicate that the plasma ionization and thermal characteristics are not modified due to the presence of the calcium matrix.     

Line selection and interference correction for the analysis of tungsten alloy by inductively coupled plasma atomic emission spectrometry

A method for the analysis of tungsten alloy to determine selected elements using inductively coupled plasma atomic emission spectroscopy is described, with emphasis on line selection and spectral interference. The spectral interference coefficients were calculated for the spectral lines of selected major and trace elements. These values were used to select analytical lines and to calibrate concentrtions of the analytes. The detection limits of the elements for this method were determined and compared with those obtained by flame atomic absorption spectrometry and direct current carbon are emission spectrometry. The results indicated that the detection limits for all of the elements determined by the proposed method are significantly better than those obtained by other techniques. In this study, the analytical reliability of the proposed method was estimated by comparison of the analytical data for the two types of tungsten alloys produced by the Korean Tungsten Company with those obtained by the matrix matching method and the results indicated that the accuracy of multi-element analysis is satisfactory.     

A comparison of inductively coupled argon plasma atomic emission spectrometry and electrothermal atomization atomic absorption spectrometry in the determination of copper and zinc in serum

Summary A comparison of performance characteristics of ICAP-AES and ETA-AAS experienced in analyzing Cu and Zn in blood serum is described. Accuracy and precision were evaluated by a statistical procedure permitting graphical representation of the results. It was concluded that ETA-AAS is very suitable for monitoring and screening purposes in toxicology and clinical chemistry whereas ICAP-AES is to be preferred when more precise determinations are required.

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Vergleich von AES mit induktiv gekuppeltem Argonplasma und AAS mit elektrothermischer Atomisierung für den Fall der Kupfer- und Zinkbestimmung im Serum

Zusammenfassung Die Leistungsfähigkeit der beiden Methoden wurde verglichen, wobei Richtigkeit und Reproduzierbarkeit statistisch mit graphischer Darstellung der Ergebnisse ausgewertet wurden. Als Schlußfolgerung ergab sich, daß sich die ETA-AAS als Überwachungs- und Screeningverfahren in der Toxikologie und klinischen Chemie eignet, während für höhere Präzision die ICAP-AES vorzuziehen ist.