Sensitivity calibration for the spark-source mass-spectrometric analysis of aluminium and its alloys

The analysis of aluminium and its alloys has been studied with use of five standards from Johnson Matthey and ten aluminium alloys from Aluminium Pechiney. The relative sensitivity coefficients for Mg, Al, Si, Ti, Cr, Mn, Ni, Cu, Zn, Sn and Pb were determined vs. iron as an internal standard. They were obtained, by using electrical detection, with a mean precision of 10% relative standard deviation. The sensitivity coefficients measured appear to be independent of the elemental concentration, but for some elements, especially the more volatile ones, remarkable changes were noticed when sparking conditions were altered and when the electrode temperature was changed by cooling with liquid nitrogen.     

Laser Ablation Inductively Coupled Plasma Mass Spectrometry for Determination of Trace Elements in Geological Glasses

 Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used as a powerful multielement analytical method for trace analysis of geological glasses which are useful as reference materials for geochemical in-situ microanalytical work. The quantification of the analytical results was carried out using the BCR-2G and NIST 612 glass standard reference material (SRM). The experimentally determined relative sensitivity coefficients (RSC) for both SRMs vary between 0.2 and 3 for most of the elements, with increasing mass an increasing of relative sensitivity coefficients was observed. The relative standard deviation (RSD) for determination of trace element concentration of most elements (N=3) are between 2 and 10%. The determination of trace elements in various geological glasses by LA-ICP-MS yielded a good agreement with the reference values and those results of other trace analytical methods. Received October 15, 1999. Revision April 14, 2000.     

Relative sensitivity coefficients for the analysis of steel by spark-source mass-spectrometry

Quantitative analysis by spark-source mass-spectrometry requires the knowledge of socalled sensitivity coefficients for the elements being determined. Five series of analyses have been carried out on five different steel standard reference materials (NBS-SRM 661-665), using photoplate detection. The relative sensitivity coefficients (S(R)) of Ti, V, Cr, Mn, Co, Ni, Cu, As, Zr, Nb, Mo, Sn, Sb, La, Ta and W were determined vs. iron as an internal standard. The S(R) values were independent of the elemental concentration. A relative standard deviation of about 15% was obtained. The accuracy as confirmed by comparing the results for a pure iron sample with those obtained by neutron-activation analysis was within the same limits.     

Quantitative investigation of Cu-Ni and Ag-Pd alloys with a laser microprobe mass analyzer

Summary Quantitative Investigation of Cu-Ni and Ag-Pd Alloys with a Laser Microprobe Mass Analyzer The analytical capability of the LAMMA-1000 instrument is discussed with respect to the evaporation and ionization probability for known concentrations of binary alloys with gradually changing composition. The relative sensitivity coefficients of Ni to Cu and Pd to Ag were found to be constant at 0.95±0.20 and 0.54±0.09, respectively, for a variety of binary alloy. No correlation with the alloy density was found for a variety of binary alloys. The ionization probability remains constant when the alloy composition changes. It is assumed that the selective evaporation does not occur within and near the laser focus. The phase transition and evaporation kinetics with respect to time and space seem to be a less dominant factor for ion formation in the LAMMA instrument. The absolute quantitative analysis is possible by the use of a calibration curve, if the total ions or the sampling volume can be determined. The use of the relative sensitivity coefficients is an effective method for a quantitative analysis with an error of 10–30%.     

Automatic sensitivity analysis of kinetic mechanisms

An algorithm for the automatic sensitivity analysis of kinetic mechanisms based on the Fourier amplitude sensitivity test (FAST) method of Shuler and co-workers is reported. The algorithm computes a measure of the relative sensitivity of each concentration to each parameter of interest, such as rate constants, Arrhenius parameters, stoichiometric coefficients, and initial concentrations. Arbitrary variations in the magnitude of the parameters are allowable. The algorithm is illustrated for the simple example of computing the sensitivity of the concentration of species A to variation of the two Arrhenius parameters for the hypothetical reaction A + A →.     

Accuracy of analysis of steels by use of a spark-source mass spectrometer with electrical detection

The precision and accuracy of spark-source mass spectrometry with electrical detection has been studied, with five steel standard reference materials (NBS-SRM 661-665). Two different modes of analysis have been evaluated, magnetic scanning with electrical detection of the individual ions in sequence, using the total ion-current as reference, and magnetic switching between masses, with current integration. Measurements of isotope abundances have been used to evaluate the precision. The relative sensitivity coefficients of Ti, V, Cr, Mn, Co, Ni, Cu, As, Zr, Nb, Mo, Sb, La, Ta and W have been determined vs. iron as an internal standard. The accuracy of analyses based on these experimentally measured relative sensitivity coefficients was confirmed by comparing the results for a pure iron sample with those obtained by neutron-activation analysis.     

Characterization of coal fly-ash particles by laser microprobe mass spectrometry

Laser microprobe mass spectrometry (LMMS) was applied to coal fly-ash particles prefractionated to homogeneous composition with respect to particle size and density. For major elements, semiquantitative results (<50% relative standard deviation) were obtained; and the characteristic density dependence found for Si, K, Ca and Fe was in good agreement with that obtained by scanning electron microscopy/energy-dispersive x-ray analysis (EDX). The relative sensitivity coefficients, based on concentrations evaluated from the EDX data, coincided with those obtained for the NBS glass particle standard in previous work.     

Complications in the Use of the Taylor Dispersion Method for Ternary Diffusion Measurements: Methanol + Acetone + Water Mixtures

The Taylor dispersion technique is used to measure the ternary mutual diffusion coefficients of aqueous nonelectrolyte solutions at 25°C. The dispersion of the injected solutes is recorded by a differential refractometer and an ultraviolet-visible detector. The diffusion coefficients are calculated directly by fitting the theoretical dispersion equations to about six experimental curves simultaneously. If the ternary diffusion effects in the measured dispersion profiles are not confused by the inaccuracy of the experimental method or an unfavorable relative detector sensitivity, the diffusion coefficients are precise. For the system methanol + acetone + water, it is shown that the Taylor dispersion method is unsuitable for the determination of all the diffusion coefficients if the methanol mole fraction is less than 0.45 or the acetone mole fraction if more than 0.001.     

Temperature‐dependent feature sensitivity analysis for combustion modeling

Sensitivity analysis is one of the most widely used tools in kinetic modeling. Typically, it is performed by perturbing the A‐factors of the individual reaction rate coefficients and monitoring the effect of these perturbations on the observables of interest. However, the sensitivity coefficients obtained in this manner do not contain direct information on possible temperature‐dependent effects. Yet, in many combustion processes, especially in premixed flames, the system undergoes substantial temperature changes, and the relative importance of individual reaction rates may vary significantly within the flame. An extension of conventional sensitivity analysis developed in the present work provides the means of identifying the temperatures at which individual reaction rate coefficients are most important as a function of input parameters and specific experimental conditions. The obtained information is demonstrated to be of critical relevance in optimizing complex reaction schemes against multiple experimental targets. Applications of the presented approach are not limited to sensitivities with respect to reaction rate coefficients; the method can be used for any temperature‐dependent property of interest (such as binary diffusion coefficients). This application is also demonstrated in this paper. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 282–295, 2005     

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.     

辉光放电质谱法测定稀土矿中的15种稀土元素

利用高纯铜粉与稀土矿石粉末均匀混合压片制样.混合15种高纯稀土氧化物制样建立标准工作曲线,校正15种稀土元素相对灵敏度因子,再进行定量分析.结果 表明,稀土元素工作曲线的线性方程相关系数R2均大于0.996,相对标准偏差(RSD)小于5％,满足定量分析要求.测定结果与电感耦合等离子体质谱法(ICP-MS)和电感耦合等离...     

典型燃料点火延迟时间的一阶和二阶局部和全局敏感度分析

Sensitivity analysis is an important tool in model validation and evaluation that has been employed extensively in the analysis of chemical kinetic models of combustion processes. The input parameters of a chemical kinetic model are always associated with some uncertainties, and the effects of these uncertainties on the predicted combustion properties can be determined through sensitivity analysis. In this work, first- and second-order global and local sensitivity coefficients of ignition delay time with respect to the scaling factor for reaction rate constants in chemical kinetic mechanisms for combustion of H₂, methane, n-butane, and n-heptane are examined. In the sensitivity analysis performed here, the output of the model is taken to be natural logarithm of ignition delay time and the input parameters are the natural logarithms of the factors that scale the reaction rate constants. The output of the model is expressed as a polynomial function of the input parameters, with up to coupling between two input parameters in the present sensitivity analysis. This polynomial function is determined by varying one or two input parameters, and allows the determination of both local and global sensitivity coefficients. The order of the polynomial function in the present work is four, and the factor that scales the reaction rate constant is in the range from 1/e to e, where e is the base of the natural logarithm. A relatively small number of sample runs are required in this approach compared to the global sensitivity analysis based on the highly dimensional model representation method, which utilizes random sampling of input (RS-HDMR). In RS-HDMR, sensitivity coefficients are determined only for the rate constants of a limited number of reactions; the present approach, by contrast, affords sensitivity coefficients for a larger number of reactions. Reactions and reaction pairs with the largest sensitivity coefficients are listed for ignition delay times of four typical fuels. Global sensitivity coefficients are always positive, while local sensitivity coefficients can be either positive or negative. A negative local sensitivity coefficient indicates that the reaction promotes ignition, while a positive local sensitivity coefficient suggests that the reaction actually suppresses ignition. Our results show that important reactions or reaction pairs identified by global sensitivity analysis are usually rather similar to those based on local sensitivity analysis. This finding can probably be attributed to the fact that the values of input parameters are within a rather small range in the sensitivity analysis, and nonlinear effects for such a small range of parameters are negligible. It is possible to determine global sensitivity coefficients by varying the input parameters over a larger range using the present approach. Such analysis shows that correlation effects between an important reaction and a minor reaction can have relatively sizable second-order sensitivity coefficient in some cases. On the other hand, first-order global sensitivity coefficients in the present approach will be affected by coupling between two reactions, and some results of the first-order global sensitivity analysis will be different from those determined by local sensitivity analysis or global sensitivity analysis under conditions where the correlation effects of two reactions are neglected. The present sensitivity analysis approach provides valuable information on important reactions as well as correlated effects of two reactions on the combustion characteristics of a chemical kinetic mechanism. In addition, the analysis can also be employed to aid global sensitivity analysis using RS-HDMR, where global sensitivity coefficients are determined more reliably.     

激光溅射电离飞行时间质谱用于不锈钢无标样半定量元素分析

本文采用两套离子透镜作为离子传输系统, 发展了一种新型的激光溅射飞行时间质谱. 在优化的实验条件下对不锈钢中的各种金属元素(包括27Al, 40Ca等)都具有比较接近的灵敏度, 可用于不锈钢的无标样半定量分析.     

毛细管离子色谱-串联质谱法测定热纤梭杆菌发酵液中的低相对分子质量有机酸

建立了一种测定热纤梭杆菌发酵液中的低相对分子质量有机酸的毛细管离子色谱-串联质谱方法。探索优化了色谱和质谱的检测条件,在最佳分析条件下同时检测8种有机酸。离子色谱以KOH水溶液作为流动相进行梯度洗脱;用IonSwift MAX-100毛细管柱进行分离;在喷雾电压为3.0 kV、喷雾气压强为2 000 kPa、成源温度为275℃的条件下,选择离子监测(SIM)模式下运行质谱。结果表明,柠檬酸和异柠檬酸两种同分异构体能够得到很好的分离,8种有机酸在一定浓度范围内具有良好的线性关系,相对标准偏差为1.45%~5.99%,相关系数为0.9696~0.9986,平均加标回收率为89.0%~110.0%,8种有机酸的检出限为0.01~0.50 mg/L。该方法进样量少,灵敏度高,重现性好,能够满足实际样品的检测要求,可用于嗜热厌氧菌发酵液中低分子量有机酸的测定。     

Mass-spectrometric multielement analysis of copper and copper-base alloys, with electrical detection

Relative sensitivity coefficients have been determined for 21 elements in copper and its alloys, with iron as an internal standard, by spark-source mass-spectrometry with electrical detection and magnetic peak-switching. Twenty calibration standards ranging from pure copper to 60%-copper alloys were used. The sensitivity coefficients measured appear to be independent of the elemental concentration and are obtained with a mean precision of 15%.     

Variational sensitivity analysis of a photochemical smog mechanism

The variational method of sensitivity analysis is applied to a recent chemical kinetic mechanism for photochemical smog. It is demonstrated that the variational method is capable of readily handling a large mechanism. The analysis can be applied to a single chemical species or to an arbitrarily large group of species contained in an objective function. Examples of the use of different objective functions are given. The variational method provides temporally distributed sensitivity coefficients. Therefore, the results are presented as a time-dependent ranking of reactions in orderof decreasing importance with respect to the objective function species. This ranking permits the time-dependent relative influence of each reaction to be readily determined by inspection. Particular attention is paid to reactions governing daytime O₃ formation and nighttime NO₃ and HONO formation.     

Determination of residual solvent in pharmaceutical preparations by static headspace GC

Static headspace GC, a simple, clean technique which is easily automated, appears to be a good approach to the determination of solvent residues in pharmaceutical preparations. The feasibility of this approach has been studied with an automated system. Data is presented for the solvents designated as impurities in pharmaceutical preparations by the United States Pharmacopeia. It was found that the static headspace technique meets the United States Pharmacopeia criteria for sensitivity. The absolute area count precision was <5% relative standard deviation and correlation coefficients to a linear response were >0.999. It was concluded that the technique is viable for this application.     

液相色谱-串联质谱法快速测定饮用水中6种雌激素

建立了液相色谱-质谱法测定饮用水中17-β-雌二醇、17-α-雌二醇、17-α-乙炔雌二醇、己烷雌酚(HEX)、己烯雌酚(DES)和双烯雌酚(DE)6种雌激素的分析方法.样品经乙腈萃取,Oasis HLB柱富集净化后,采用液相色谱-质谱法测定.方法在5～100 μg/L范围内呈良好线性,相关系数为0.994～1.000...     

Determination of trace elements in geological samples by laser ablation inductively coupled plasma mass spectrometry

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was applied for the sensitive multi-element analysis of traces and ultra-traces in geological samples. In order to prepare homogeneous targets the powdered geological samples were melted together with a lithium-borate mixture (90% Li₂B₄O₇, 10% LiBO₂) in a muffle furnace at 1050?°C. The quantification of the analysis results was carried out using the BCR-2G and BM standard reference material (SRM). The experimentally determined relative sensitivity coefficients (RSC) for both SRMs vary between 0.2 and 3 for most of the elements, whereas the relative standard deviation (RSD) of the determination (N = 3) of the concentration was 5–20%. The analysis results of LA-ICP-MS for various geological samples are in agreement with those of other methods.