Investigation of plasma-related matrix effects in inductively coupled plasma-atomic emission spectrometry caused by matrices with low second ionization potentials—identification of the secondary factor

Plasma-related matrix effects induced by a comprehensive list of matrix elements (a total of fifty-one matrices) in inductively coupled plasma-atomic emission spectrometry were investigated and used to confirm that matrix effects caused by elements with a low second ionization potential are more severe than those from matrix elements having a low first ionization potential. Although the matrix effect is correlated unambiguously with the second ionization potential of a matrix, the correlation is not monotonic, which suggests that at least one other factor is operative. Through study of a large pool of matrix elements, it becomes possible to identify another critical parameter that defines the magnitude of the matrix effect; namely the presence of low-lying energy levels in the doubly charged matrix ion. Penning ionization by Ar excited states is proposed as the dominant mechanism for both analyte ionization/excitation and matrix effects; matrices with a low second ionization potential can effectively quench the population of Ar excited states through successive Penning ionization followed by ion-electron recombination and lead to more severe matrix effects.     

Relativistic contributions to single and double core electron ionization energies of noble gases

We have performed relativistic calculations of single and double core 1s hole states of the noble gas atoms in order to explore the relativistic corrections and their additivity to the ionization potentials. Our study unravels the interplay of progression of relaxation, dominating in the single and double ionization potentials of the light elements, versus relativistic one-electron effects and quantum electrodynamic effects, which dominate toward the heavy end. The degree of direct relative additivity of the relativistic corrections for the single electron ionization potentials to the double electron ionization potentials is found to gradually improve toward the heavy elements. The Dirac-Coulomb Hamiltonian is found to predict a scaling ratio of ～4 for the relaxation induced relativistic energies between double and single ionization. Z-scaling of the computed quantities were obtained by fitting to power law. The effects of nuclear size and form were also investigated and found to be small. The results indicate that accurate predictions of double core hole ionization potentials can now be made for elements across the full periodic table.     

Investigation of matrix effects in inductively coupled plasma-atomic emission spectroscopy using laser ablation and solution nebulization — effect of second ionization potential

Plasma-related non-spectroscopic matrix effects of 31 elements in inductively coupled plasma (ICP)-atomic emission spectrometry were investigated using both laser ablation and solution nebulization as sample introduction techniques. Matrix effects were studied by monitoring the excitation conditions of the plasma using the ionic to atomic spectral line intensity ratios of zinc and magnesium. A new kind of matrix interference was found in the ICP that appears to be related to matrices with elements of low second ionization potential. The matrix effects do not correlate with the first ionization potential of the element. Only those matrix elements with low second ionization potential showed severe matrix effects. Increasing the forward power of the ICP or replacing the carrier gas with a 50%/50% argon–helium mixture did not significantly reduce this matrix effect. However, using 100% helium as the carrier gas greatly reduced the extent of this matrix effect, suggesting that argon is involved in the interference mechanism. The interference mechanism may involve interactions between doubly-charged matrix ions and argon species.     

Kieselgelstandards für die Bestimmung von Spurenelementen in pulverförmigen Proben mit leichter Matrix durch Röntgenfluorescenzanalyse

The paper deals with homogeneous magnetic fields and added chemical substances both affecting the spectrochemical results obtained in arc excitation studies. The influence of a homogeneous magnetic field on the total intensity of lines of various analysis elements (Hg, Zn, Ga, Tl) in graphite has been examined. Furthermore, the axial and radial distributions of line intensities in arc plasma were determined. Parameters used were the magnetic field strength (0, 0.01, 0.02, 0.04 T) and the physical data of the analysis elements. It was found that the effect of the magnetic field varies with the ionization potential of the elements involved, their atomic mass and the strength of the magnetic field applied. A non-destructive method of measuring was introduced for studying the effects of a homogeneous magnetic field on the rates of evaporation. The results showed increased evaporation rates in presence of magnetic fields as a function of the evaporation heat of the elements involved. Effects of Ga₂O₃ additive on the line intensities of impurity elements are governed by the Ga₂O₃ concentration and the ionization potential of the elements examined.     

Theoretical Calculations of Relative Ion Yields for Glow Discharge Mass Spectrometry

Quantitative determination of the elemental composition of metals and other solids by glow discharge mass spectrometry requires a calibration factor for each element. In past work, these factors, called relative ion yields (RIYs), have been determined experimentally from the mass spectra of standards of certified composition. The RlYs of some elements were found to be over 10 times larger than the RIYs of other elements. In this study a simple calculation of the RIYs of the elements within the same sample is derived from a theoretical framework which takes into account the combined effects of sputtering and ionization. The ionization function involves the electron affinity and the first ionization potential of each element, plus two unknown parameters. By favorable selection of a temperature parameter and a chemical-potential parameter, the RIYs calculated by this method were found to agree satisfactorily with the experimental RlYs of former work. The temperature of 16,000 K (used in this work) corresponds to an average electron energy of ～ 2 eV.     

Experimental studies of charge transfer reactions between argon and the third row metals calcium through copper in the inductively coupled plasma

The effect of charge transfer reactions on analyte excitation and ionization in the inductively coupled plasma was studied by two independent techniques. In one technique, pulsed lasers were used to either deplete the ground state of neutral analyte atoms or enhance the population of selected states of the singly charged ion. In both cases the perturbed species were collision partners with argon in potential charge transfer reactions. The effects of charge transfer collisions could be detected in the form of changes in emission from product species. In the second technique, a simple correlation method was used to detect the link via charge transfer of neutral atom ground states and highly excited ionic levels. In the presence of charge transfer collisions, the populations of such linked levels show strong positive correlations. The two techniques were used to study the effects of charge transfer reactions on the third row elements Ca–Cu. With the exception of Cr and Mn, all of the elements studied showed positive evidence of excitation and ionization by charge transfer collision with argon.     

微量进样/ICP-MS体系中的基体效应研究

考察了自行组装的高效微量进样系统在22μL/min低提升量下电感耦合等离子体质谱的基体效应.质量数和电离电位不同的基体元素质量浓度为2g/L时,低质量数分析元素受到一定的干扰,而对于高质量数分析元素,其信号几乎不受基体元素干扰,归一化信号值接近1.对于体积分数为5%的有机基体样品溶液,此微量高效雾化系统测得的归一化信号值多接近0.5.实际样品中常见的基体元素K,Na,Ca和Mg质量浓度低于500mg/L,以及乙醇和乙酸体积分数小于1%时,微量进样系统均不产生显著干扰.     

流动注射-电感耦合等离子体质谱法的基体效应

研究了流动注射小体积进样,电感耦合等离子体质谱法的在体效应,并与连续进样作了比较,流动注射小体积（１００μＬ）进样时,电离电位较高的Ａｓ和Ａｕ基体对分析元素的信号表现为增强效应,分析元素的质量数越大,所受增强效应越小。了电位较低的Ｃｕ、Ｉｎ、Ｌｉ、Ｎａ和Ｐｂ基体对分析元素的信号则表为抑制效应,基体元素的质量数越大,对分析元素的抑制效应也越大;质量数较大的分析元素,所受的抑制效应较;对质量数相近的分析元素,电离电位较高者受的抑制较大,与连续进样相比,流动注射小体积进样时,基体元素对分析元素的抑制效应较弱,而增强效应较强。     

Vertical ionization potential in hydrogen molecule with many-body Green's function method

The many-body Green's function method is applied to the vertical ionization potential of the hydrogen molecule. The ionization potential is calculated iteratively by expanding the self-energy part up to third order. The effects of higher-order correlation corrections and nondiagonal self-energy elements on the solutions of the Dyson equation are examined with some techniques and approximations, by means of which a Koopmans' defect of 97.7% of the accurate value is obtained.     

Influence of wavelength,irradiance, and the buffer gas pressure on high irradiance laser ablation and ionization source coupled with an orthogonal Time of Flight Mass Spectrometer

Influence of laser wavelength, laser irradiance and the buffer gas pressure were studied in high irradiance laser ablation and ionization source coupled with an orthogonal time-of-flight mass spectrometer. Collisional cooling effects of energetic plasma ions were proved to vary significantly with the elemental mass number. Effective dissociation of interferential polyatomic ions in the ion source, resulting from collision and from high laser irradiance, was verified. Investigation of relative sensitivity coefficients (RSC) of different elements performed on a steel standard GBW01396, which was ablated at 1064 nm, 532 nm, 355 nm, and 266 nm, has demonstrated that the thermal ablation mechanism could play a critical role with the first three wavelengths, while 266 nm induces non-thermal ablation principally. Experimental results also indicated that there is no evident discrepancy for most metal elements on RSCs and LODs among four wavelengths at high irradiance, except that high boiling point elements like Nb, Mo, and W have higher RSCs at higher irradiance regions of 1064 nm, 532 nm, and 355 nm due to thermal ablation. A geological standard and a garnet stone were also used in the experiment subsequently, and their RSCs and LODs for metal elements show nonsignificant dependence on wavelength at designated irradiances. All results reveal that relatively uniform sensitivity can be achieved at any wavelength for metal elements in the solids used in our experiments at an appropriate irradiance for the low pressure high irradiance laser ablation and ionization source.     

Core polarization and relativistic effects competition in the first ionization potentials for some systems in the Cu,Ag, and Au isoelectronic sequences

Single-configuration relativistic Hartree–Fock values of the first ionization potentials for Cu through Kr⁷⁺, Ag through I⁶⁺, and Au through Pb³⁺ are computed in “frozen” and “relaxed core” approximations with and without allowance for core polarization. Effects of polarization of the atomic core by the valence electron are included by introducing a polarization potential in the one-electron Hamiltonian of the valence electron. The core polarization potential depends on two parameters, the static dipole polarizability of the core α and the cut-off radius r₀, which are chosen independently of the ionization potential data. It is demonstrated that by including the core polarization potential with α and r₀ parameters, which are simply chosen instead of being empirically fitted, it is still possible to account, on the average, for at least 70% of the discrepancy between the single-configuration relativistic Hartree–Fock ionization potentials and the experiment, a discrepancy usually ascribed to the contribution of valence-core electron correlations, and to bring the theoretical ionization potentials to an average agreement with experiment of around 1%. It can be concluded from this study that for low and medium Z elements the core polarization dominates for neutral systems or systems in low ionization stages, whereas for highly ionized systems the relativistic effects prevail. For heavy elements, however, the core polarization influence is comparable to the relativistic one only for neutral systems, whereas for ions the relativistic effects are overwhelmingly predominant.     

SCF Dirac-Hartree-Fock calculations in the periodic system

Binding energies calculated by DHF method were compared with modified DFS method calculations and experimental values. First ionization potentials of all elements from Z=1 to Z=120 (excluding the lanthanide and actinide series) were obtained from DHF values. These calculated values were compared with spectroscopically determined first ionization potentials for the region Z=1 to Z=88. The obtained ratios of DHF calculated and experimental values in the Z88 region (correlation ratios) were extrapolated for 104–120 elements and used in correcting calculated DHF eigenvalues to obtain expected values for the first ionization potential in this region.     

Simplex optimization of a nitrogen-cooled argon inductively coupled plasma for multi-element analysis

A medium power (5 kW) nitrogen-cooled argon inductively coupled plasma (ICP) system was used in an investigation of the basic and modified simplex methods of optimization. The optimum operating conditions for the ICP system were established for 23 commonly determined elements covering a wavelength range from 180 to 340 nm and including an approximately equal number of atomic and ionic lines.Initially the optimization was carried out for individual elements on the basis of two responses: net signal-to-background ratio (SBR) and ionization interference (II).The simplex technique indicated a need to improve the nebulization system.In achievement of maximum SBR, interesting correlations were found between the optimum power required, on the one hand, and the difficulty of excitation of the elements and the optimum intermediate-gas flowrate, on the other.Finally a method for optimization of the conditions for the plasma in multi-element analysis, based on the sequential use of maximum SBR and minimum ionization interference (MII) responses, was devised and successfully tested against several routine analytical methods. Application of the conditions established during these optimizations result in an analytically useful plasma giving good detection limits as well as minimum ionization interference effects.     

Principle and analytical applications of resonance lonization mass spectrometry

Resonance ionization mass spectrometry (RIMS) is a very sensitive analytical technique for the detection of trace elements. This method is based on the excitation and ionization of atoms with resonant laser light followed by mass analysis. It allows element and, in some cases, isotope selective ionization and is applicable to most of the elements of the periodic table. A high selectivity can be achieved by applying three step photoionization of the elements under investigation and an additional mass separation for an unambiguous isotope assignment.An effective facility for resonance ionization mass spectrometry consists of three dye lasers which are pumped by two copper vapor lasers and of a linear time-of-flight spectrometer with a resolution better than 2500. Each copper vapor laser has a pulse repetition rate of 6.5 kHz and an average output power of 30 W.With such an apparatus measurements with lanthanide-, actinide-, and technetium-samples have been performed. By saturating the excitation steps and by using autoionizing states for the ionization step a detection efficiency of 4 × 10^–6 and 2.5 × 10^–6 has been reached for plutonium and technetium, respectively, leading to a detection limit of less than 10⁷ atoms in the sample. Measurements of isotope ratios of plutonium samples were in good agreement with mass-spectrometric data. The high elemental selectivity of the resonance ionization spectrometry could be demonstrated.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria     

Relativistic two-component infinite order method for atomic core ionization potentials

In this paper the authors have applied the infinite-order two-component method (IOTC) to compute the valence and inner shell ionization potentials for the Ne, Ar, Kr, and Xe elements. The obtained results show the very good performance of the recently defined relativistic IOTC method. They also confirm the importance of the relativistic effects in the determination of the inner shell ionization potentials.     

Multiple ionization effects on total L-shell X-ray production cross sections by proton impact

The effect of multiple ionization on total L-shell X-ray production cross sections by proton impact, with energies below 1 MeV, on elements with atomic numbers in the range 26–55 was studied. Measurements of those cross sections for several elements were also done to enlarge the experimental database. Several tables for atomic parameters (fluorescence yields and Coster–Kronig transition probabilities) were used. The agreement between theory and experiment was optimized when average fluorescence yields given by Hubbel et al. (J. Phys. Chem. Ref. Data 23(2) (1994) 339) and a multiple ionization model proposed by Lapicki et al. (Phys. Rev. A 34(5) (1986) 5813) were used together. Thus, improvements to theoretical predictions for ionization cross sections should consider first a correct set of atomic parameters.     

The first ionization potential of uranium and thorium measured in a d.c. arc plasma

Tha Saha relationship was used to derive the ionization potentials of uranium and thorium from measurements of temperature or of electron density in a plasma in thermodynamic equilibrium. Introducing into the plasma elements with well defined ionization potentials, such as Ba, Al, V, Cr, Zr, Mo, Cu, Si and some of the rare-earths, as matrices, the temperature and electron density were measured in the central region of the arc plasma. A relation was established between the different ionization potentials and the plasma temperature or the electron density. From this relation the values of 6.3 ± 0.3 and 7.5 ± 0.3 eV were found for the ionization potentials of U and Th respectively.     

Metal dicarbides as intermediate species in thermal ion formation mechanisms

Lanthanide elements (lanthanum to lutetium) and actinide elements (uranium and plutonium) adsorbed onto resin beads and mounted on rhenium filaments were studied as thermal ionization sources. Temperatures at which these ion sources gave maximum intensities were measured for each of these elements. The temperature trends correlate with the dissociation energies of the corresponding metal dicarbide compounds. The metal dicarbide functions as a carrier to take the lanthanide and actinide elements to higher temperatures than would be attainable otherwise. This results in release of the atomic species at a higher temperature where ionization probability is significantly increased.     

Spatially resolved ultra-trace analysis of elements combining resonance ionization with a MALDI-TOF spectrometer

A combined setup for spatially resolved mass analysis of trace amounts of elements and macromolecules is presented. Using a MALDI-TOF mass spectrometer, a laser spectroscopic setup for resonant ionization of neutral atoms has been implemented. This allows for an efficient and selective detection of trace elements by means of resonance ionization mass spectrometry (RIMS). The instrumental scheme is described, and methodological developments are presented. In a first application pure, laser desorption/ionization with TOF-MS was used to measure mass distributions of cosmic nanodiamonds. For further applications regarding the spatially resolved ultra-trace analysis of elements in solid samples, an implanted target was used to characterize both laser desorption/ionization and laser desorption/resonance ionization for the detection of trace elements within. A perspective of the setup is given and future investigations are outlined.