New Approach to the Calculation of Relative Sensitivity Factors in Inductively Coupled Plasma Mass Spectrometry

The relative sensitivity factors (RSFs) of 68 elements in inductively coupled plasma mass spectrometry were determined. The ionization process in an inductively coupled plasma was found to be only approximately described by the Saha–Eggert equation. A relationship between the RSFs and the absolute electronegativities of atoms was found. This factor has the strongest effect on the accuracy of the calculations of RSFs for chemically active elements. The average relative systematic error of the calculations of RSFs taking into account absolute electronegativity was reduced to 0.30.     

原子电负性和极化度对卤代甲烷C 1s电子电离能的影响

以原子的电负性χP和极化度α为基本参数, 估算卤代甲烷CHnY4−n−mZm(Y, Z=F, Cl, Br, I) C 1s电子电离能的电荷效应和松弛效应. 电荷效应由C—H和C—Y(Z)键两端原子的电负性差来度量, 松弛效应由碳原子带的电荷乘上氢和卤素原子极化度来衡量, 进而用电荷效应和松弛效应一起表达卤代甲烷中C 1s电子电离能的静电-松弛屏蔽效应ΔSi. 将ΔSi代入类-Slater模型, 得到卤代甲烷中C 1s电子电离能E1,C的估算方程, 该方程的相关系数r=0.99987, 对27个卤代甲烷的计算值与实验值之间的平均绝对误差仅为0.038 eV, 小于实验误差0.1 eV. 同时, 用留一法(leave-one-out)进行交叉验证(相关系数rcv=0.99977, 预测值与实验值之间的绝对平均误差只有0.049 eV), 结果表明所得方程具有良好的预测能力和稳定性.     

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.     

覆氧或氧离子轰击下固体表面二次正离子发射的研究

通过对离子轰击下固体表面电离过程重新考虑认为，在固体表面覆氧或氧离子轰击下除表面原子的直接电离外，激发态双原子间电子交换和断键亦起重要作用。在此基础上修正了局部热力学平衡模型，得到了一个包含各类离子内配分函数、电离能、金属－氧原子键断键能以及表面金属原子与氧原子结合份数等参数决定的新电离几率分析表达式。应用该分析表达式解释了金属表面覆氧、氧离子轰击金属、化合物半导体表面二次离子发射中氧增强效应、充氧量对二次离子发射的影响及其基体效应等实验现象。并由此得到了元素相对灵敏度因子的分析表达式，对化合物半导体及一些陶瓷材料表面二次离子质谱分析中元素灵敏度因子随元素电离能变化曲线给予了相应的物理解释。     

Compensation of gradient related effects when using capillary liquid chromatography and inductively coupled plasma mass spectrometry for the absolute quantification of phosphorylated peptides

The application of reversed phase liquid chromatography (RP-LC) hyphenated to inductively coupled plasma mass spectrometry (ICP-MS) for the accurate quantification of bio-molecules via covalently bound hetero atoms such as phosphorus is restricted, due to the known effects of increasing amounts of organic solvents on the ionization behavior of certain elements. An approach for the compensation of variations in the elemental response, due to changes in the solvent composition during the RP gradient separation of phosphorylated peptides is described, which includes the application of a second, matched reversed gradient, that is mixed post-column with the RP column outflow before entering the LC–ICP-MS interface. The experimental design allows the application of gradient separations, while the element-specific detection is carried out under isocratic conditions with a constant organic solvent intake into the plasma. A constant elemental response is a general pre-requisite for the application of ICP-MS for the absolute quantification of peptides via their hetero atom content, especially when no corresponding high purity standards are available or natural mono-isotopic hetero element tags are utilized. As complementary technique LC–electrospray ionization linear ion trap mass spectrometry (ESI-QTRAP-MS) has been used for peptide identification and to elucidate their phosphorus stoichiometry. Highly reproducible separations have been obtained with retention time and peak area RSDs of 0.05% and 7.6% (n = 6), respectively. Detection limits for phosphorus of 6 μg L⁻¹ (6 pg absolute), have been realized, which corresponds to approximately 200 fmol of an average molecular weight, singly phosphorylated peptide. In addition an automatic routine for flow injection analysis (FIA) at the end of each chromatographic separation has been developed, to calibrate each chromatographic separation, which allows absolute quantification of the separated species, whenever their tag stoichiometry is known. Phosphorylated peptides as well as tryptic protein digests have been used as model compounds for method development and to demonstrate the applicability of the proposed setup for phosphopeptide quantification on the basis of simple inorganic phosphorus standards.     

Slater-like model for carbon 1s core ionization energies of halomethanes.

Based on the atomic electron affinity EA, the average energy of the valence-shell electrons EI and the polarizability alpha, the charge effect and the relaxation effect were evaluated for the carbon 1s core ionization energies of halomethanes CHnY4-n-mZm (Y, Z=F, Cl, Br, I). The charge effect was scaled by the electronegativity discrepancy (the discrepancy of EA and the discrepancy of EI between the C and H or halogen atom in the C-H or C-halogen chemical bond). The relaxation effect (induced dipole) was scaled by the charge on the carbon atom together with the polarizability of the H and halogen atoms. Further, the electrostatic relaxation shielding DeltaSi of the carbon 1s electron in the halomethane was expressed by the charge effect together with the relaxation effect. By introducing DeltaSi into the Slater model, a Slater-like model was obtained for calculating the carbon 1s core ionization energy E1,C of halomethane, whose correlation coefficient r is 0.99985 and the average absolute error is only 0.041 eV between the calculated and the experimental carbon 1s core ionization energies for 27 halomethanes. Also the cross-correlation was tested by the leave-one-out (LOO) cross-validation method, and the obtained model has good predictive ability and stability (the correlation coefficient rcv is 0.99976, the average absolute error between the predicted and the experimental values is only 0.052 eV). The proposed model perhaps lays a good foundation for computing the core ionization energies of various atoms in more complex molecules.     

Diagnostic and analytical study of post ablation ionization of neutral atoms of major and minor constituents from a low alloy steel

Post ablation ionization (PAI) of neutral atoms from a low alloy steel has been investigated using non-resonant laser ionization in a time-of-flight mass spectrometer. By varying the delay between the ablation and ionization lasers, the velocity distributions of the Ti, V, Cr, Mn and Fe atoms have been determined simultaneously. These distributions have been recorded as a function of ablation laser fluence. The half-range Maxwell-Boltzmann velocity distribution has been used to fit the data and different characteristic temperatures have been determined for the various elements in the sample. The quantitative capability of this method for bulk and surface analysis has been evaluated by calculating the relative sensitivity factors (RSFs) for the various constituent elements. The RSFs for all of the elements are seen to be highly dependent on the delay between the ablating and ionizing lasers. This dependence was reduced by integrating the temporal dependent ion yield, leading to a significant improvement in the calculated RSF values. It was also found that the RSFs were not highly dependent on the power density of the ablation laser beam.     

Implementation of pseudopotential in the G3 theory for molecules containing first-, second-, and non-transition third-row atoms

Compact effective pseudopotential (CEP) is adapted in the G3 theory providing a theoretical alternative referred to as G3CEP for calculations involving the first-, second-, and non-transition third-row elements. These modifications tried to preserve as much as possible the original characteristics of G3. G3CEP was used in the study of 247 enthalpies of formation, 22 atomization energies, 104 ionization potentials, 63 electron affinities, and 10 proton affinities, resulting in the calculation of 446 species for the first-, second-, and third-row atoms. The final average total absolute deviation was of 1.29 kcal mol(-1) against 1.16 kcal mol(-1) from all-electron G3 for the same calculations. The CPU time has been reduced by 7% to 56%, depending on the size of the molecules and the type of atoms considered.     

Role of electronegativity in the qualitative inference of the TOF-SIMS fragment pattern of inorganic compounds

The role of the electronegativity of atoms in inorganic compounds in TOF-SIMS fragmentation is discussed. From a study of approximately 30 inorganic compounds--chlorides, oxides, nitrates, and sulfates--a simple rule has been proposed for the dependence of fragment pattern appearance on the electronegativity (electron affinity), which can be easily obtained from handbooks, and the valence of positive and negative ions in these compounds. TOF-SIMS measurements of metal and alloy surfaces, should be corrected for the ionization potentials and/or electronegativities of atoms present in surface contaminants.     

有机化合物对电感耦合等离子体质谱(ICP-MS)法测定食品中总砷的影响

目的 研究有机化合物对电感耦合等离子体质谱法（ICP-MS）测定食品中总砷的影响,分析总结一般规律,为食品中总砷的准确测定提供理论依据。方法 研究了甲醇和乙醇等14种有机化合物对ICP-MS测定砷的动能歧视模式（KED）信号值和动态反应模式（DRC）信号值的影响,通过分析各有机化合物的电离能、极性和溶解度等性质,推测其在ICP-MS测定体系中对砷响应信号值增敏或者抑制的可能机理。结果 有机化合物对ICP-MS的KED模式测定砷离子As+的信号值有增敏效应,对DRC模式测定氧化砷离子AsO+信号值的影响小于KED模式测定As+的信号值,而且过程也更为复杂。相反,氮氧化物会减弱As+和AsO+的信号值。锗、铟等内标元素原子与砷原子在等离子体中电离行为和灵敏度的差异,使得内标元素校准砷测定信号的漂移受到干扰。结论 推测有机化合物影响ICP-MS测定砷响应信号值的可能机理是：有机化合物和氮氧化物经电离或裂解之后分别生成碳离子或多原子碳离子和氮氧离子或氮氧基团,碳离子或多原子碳离子会与砷原子发生电荷转移反应,增强As+或AsO+的信号值,同时有机化合物也可能会与As+竞争氧气而降低AsO+的信号值,而具有强电负性的氮氧基团可能会与As+和AsO+发生电荷转移反应而减弱其信号值。有机化合物对砷的ICP-MS响应信号值的影响可能是受到有机化合物电离能、溶解度、极性和分子结构等综合因素的结果。     

A small high‐irradiance laser ionization time‐of‐flight mass spectrometer

A small high‐irradiance laser ionization time‐of‐flight mass spectrometer (LI‐TOFMS) with orthogonal sample introduction was described. High irradiance of 6 × 10¹⁰ W/cm² at 532 nm from a Nd : YAG laser was applied in the experiment to get a high ionization degree in plasma and to dissociate the interferential polyatomic ions. Meanwhile, the interferential multiply charged ions resulted by high‐irradiance were nearly eliminated in the spectrum by utilizing helium as the buffer gas in the ion source due to three‐body recombination, which resulted in a relatively clean background. Improved signal stability was obtained by automated step moving of the sample stage in short time intervals. By using two sets of Einzel lens in transport system, nearly uniform relative sensitivity coefficients (RSCs) were achieved for most of metal elements including light ions which were detected in extremely low sensitivity in previous hexapole transportation instrument. The resolving power reaches 2200, and the detection limits (DLs) are 10^?6 g/g for metal elements in the steel standard. Copyright © 2009 John Wiley & Sons, Ltd.     

Survey Analysis by Inductively Coupled Plasma Mass Spectrometry without the Use of Standard Reference Materials

The reference-free analysis of a standard solution containing 21 elements was performed on an inductively coupled plasma mass spectrometer. The relative sensitivity coefficients of the elements were calculated taking into account the absolute electronegativities of atoms in accordance with the new approach that was developed previously for single-element solutions. The accuracy was evaluated. The results obtained using the new approach were compared with the data calculated by the Saha–Eggert equation and a quasi-equilibrium model, which use ionization potentials.     

Consideration on excitation mechanisms in a high-power two-jet plasma

The study of excitation mechanisms in the region before the jet confluence of a high-power two-jet plasma used for analysis of different powders has been undertaken. Distribution of excited levels of Fe atoms and ions according to the Boltzmann population was found. Measuring Fe atomic and ionic excitation temperatures showed their considerable difference (≈ 2000–2500 K). The effect of argon on line intensities of a wide range of elements was investigated by the experiment with argon covering. A negligible effect of argon covering on line intensities of atoms with ionization energy of < 8 eV allows one to assume their predominant excitation by electron impact. The argon participation in excitation of atoms having ionization energy of > 8 eV was revealed. This is likely to be due to Penning ionization by metastable argon followed by ion recombination with an electron and stepwise de-excitations. A more pronounced effect of argon covering was observed for ionic lines of investigated elements with total excitation energy ranging from 11 to 21 eV. Penning ionization followed by electron impact is believed to be a probable mechanism for ion excitation. The contribution of metastable argon to excitation processes results in departure from local thermodynamic equilibrium and different atomic and ionic excitation temperatures.     

Radii of Redox Components from Absolute Redox Potentials Compared with Covalent and Aqueous Ionic Radii

Aqueous standard potentials, referred to that of the SHE as zero, were recently shown to vary linearly with gaseous ionization potentials, with the absolute potential of SHE as the intercept. This enabled arriving at the absolute redox potentials of elements. Here, the distances between the oxidized and reduced forms in aqueous solutions have been evaluated. From the linear dependence of these distances on the covalent radii of atoms, the radii of the redox components have been obtained. The latter also vary linearly with the aqueous ionic radii estimated earlier from ion‐water distances, and indicate the presence of aqueous molecular anions.     

电负性研究Ⅰ.建立元素电负性标度的有效核电荷数方法

通过价层电离能、价键轨道能量用有效核电荷数法建立了周期表中 90种元素的电负性新标度。χ=0 .41 2 3 -EV,该式表明电负性值与价键轨道能量的绝对值的平方根成正比 ,所得数值是一套无量纲的相对参数。元素电负性值随价态的升高与元素非金属性的增强相对应 ,元素电负性的大小不仅与单个成键电子有关 ,而且也与参加价键作用的多个电子甚至整个价层都有紧密的联系。氢的元素电负性值不同于Pauling值、等于 1 .52。用 1 6种氢化物中键的额外离子能Δ′对 (χA-χB) 2 作图 ,两者之间确实具有良好的线性关系。本方法充分体现了目前公认的三大电负性标度的优点 ,该标度同时也是价层电子在价键状态下的一种能量标度 ,是对元素周期律的定量描述和反映。     

An empirical chemical potential of the atomic core for non-transition element

An empirical relation between the energy of an atomic ion and its charge is determined from the experimental ionization potentials for non-transition elements. The definition of chemical potential μ_c and effective charge Z_c of the atomic core is postulated. Both are shown to be closely related to the classical electronegativity.     

Effect of Ar/H2 and Kr/H2 mixtures as discharge gas on the ion intensity in dc glow discharge mass spectrometry

 In dc glow discharge mass spectrometry, the addition of small amounts of H₂ to pure Ar as discharge gas has greatly increased the ion intensities of elements compared with the conventional method using pure Ar. This phenomenon was also observed for the addition of H₂ to pure Kr. The reason for the increase of the ion intensities of elements was studied by using a Kr gas mixture containing 0.2% (v/v) H₂. The ion intensities of the elements P, Se and As (whose first ionization potentials are higher than the energy levels of the excited state of Kr) did not increase even if the Kr/H₂ gas mixture was used. The results show that the addition of H₂ significantly contributed to increasing the number of metastable argon or krypton atoms (Penning ionization). Received: 4 November 1995/Revised: 5 January 1996/Accepted: 10 January 1996     

Effect of Ar/H2 and Kr/H2 mixtures as discharge gas on the ion intensity in dc glow discharge mass spectrometry

 In dc glow discharge mass spectrometry, the addition of small amounts of H₂ to pure Ar as discharge gas has greatly increased the ion intensities of elements compared with the conventional method using pure Ar. This phenomenon was also observed for the addition of H₂ to pure Kr. The reason for the increase of the ion intensities of elements was studied by using a Kr gas mixture containing 0.2% (v/v) H₂. The ion intensities of the elements P, Se and As (whose first ionization potentials are higher than the energy levels of the excited state of Kr) did not increase even if the Kr/H₂ gas mixture was used. The results show that the addition of H₂ significantly contributed to increasing the number of metastable argon or krypton atoms (Penning ionization). Received: 4 November 1995/Revised: 5 January 1996/Accepted: 10 January 1996