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.     

Comparison of sensitivity coefficients for spark-source mass spectrometry determined with photographic and electrical detection

Relative sensitivity coefficients have been determined for the spark-source mass-spectrometric analysis of iron and steel samples with photographic and electrical detection. The data differ significantly for elements with mass considerably different from the internal standard, iron, mainly because of the different dependence of the response of the detectors on the ion mass. After correction for this effect and for the smaller influence of ion energy distribution and collector slit setting, fair agreement is obtained between sensitivities in both detection modes.     

Analysis of gallium arsenide by spark-source mass-spectrometry

A method has been developed for analysing gallium arsenide with a resistance of greater than 10(9)Omega by spark-source mass-spectrometry, without the need for pelleting, which introduces a prohibitively high level of contamination and lowers the detection limit for a given exposure. It uses a gold evaporation technique, whereby a thin layer of 99.999% pure gold is deposited on one surface of the GaAs electrodes, in a chamber mounted on the ion-source. No contamination, other than gold, is introduced into the sample at a level of 50 ng/g or greater. It is possible to detect carbon in the sample at the 1-2 mug/g level. The sample preparation time is less than 30 min, and more than one set of samples can be gold-coated at a time.     

Relative sensitivity coefficients for rare earths in spark-source mass spectrometry

Relative sensitivity coefficients have been computed for rare earth elements according to empirical models which have been proposed in the literature. Explanations concerning differences between the computed and observed values are based upon possible instrumental discrimination effects which negate some processes occurring in the ion source. Computations relating elemental physical constants to observed results in a semi-random manner are shown which support this contention.     

A comparison between secondary-ion mass-spectrometry and spark-source mass-spectrometry for the quantitative analysis of steel wire

A comparison has been made between the results of the matrix-ion species ratio (MISR) method for quantification of secondary-ion mass-spectrometry data and spark-source mass-spectrometry analysis using photoplate detection for analysis of the steel basis of AlZn coated wire products. For SIMS quantification a suitable set of sensitivity factors, corrected for the actual surface sampling condition, was used. The results of both methods compare well. The SIMS results were, for most elements, within 25% of the concentration determined by SSMS. This could indicate that reasonably accurate results can be obtained by using the matrix-ion species ratio method for SIMS.     

Improvement of reproducibility of trace analysis by spark-source mass-spectrometry

Summary Mechanisms responsible for poor reproducibility of analysis by spark-source mass-spectroscopy are discussed. A new scheme for the output cascade of a radiofrequency generator has been developed. It allows for stabilizing both the charge and impurity mass-spectrum composition at changing the width of the interelectrode gap over a wide range. The causes of transient irreproducibility in mass-spectrometric analysis have been studied and traced to temporal variation in the discharge-circuit parameters. Methods of eliminating this irreproducibility are proposed.

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Verbesserung der Reproduzierbarkeit der funkenmassenspektrometrischen Spurenanalyse

Zusammenfassung Die Ursachen der schlechten Reproduzierbarkeit der mit Hilfe der Fun-kenmassenspektrometrie durchgeführten Spurenanalyse wurden erörtert. Ein neues Schema der Ausgangsstufe des Hochfrequenzgenerators wurde ausgearbeitet. Dies ermöglicht die Konstanthaltung sowohl der Ladung wie der Zusammensetzung des Massenspektrums auch bei weitgehender Veränderung des Elektroden-Zwischenraumes. Die Ursachen der vorübergehenden Nicht-Reproduzierbarkeit massenspektrometrischer Analysen wurden untersucht. Diese wird von der zeitlichen änderung der Ladungsparameter verursacht. Vorschläge für die Behebung dieser Nicht-Reproduzierbarkeit wurden gemacht.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Effects of several experimental parameters on the relative sensitivity factors in spark-source mass spectrometric analysis of steel

The effects of spark gap, sample electrode size, spark technique, spark position, and energy-pass bandwidth of the ion beam, on the relative sensitivity factors in analysis for trace elements in steel by spark-source mass spectrometry have been investigated by means of electrical-detection, peak-switching techniques. The effects of spark gap and spark position are of the greatest importance. The energy distributions of both matrix and impurity ions were measured. For several elements, changes in spark position produced corresponding changes in the distribution of ion energies. These changes of energy distribution were partly responsible for variations in relative sensitivity factors with changing spark position.     

Influence of matrix on relative sensitivity factors in spark-source mass spectrometric analysis

In spark-source mass spectrometric analysis, relative sensitivity factors are commonly used for sensitivity correction. The influence of matrix elements (aluminum, iron, copper and molybdenum) on such factors was studied under similar experimental conditions. The factor relative to iron, which is contained in the above four metals, varied with the matrix, but an equation based on the independent correlation of matrix and measured element with a physical property of these elements, was satisfactory. Melting point gave a better multiple correlation than boiling point or heat of sublimation. From this equation under given experimental conditions, it should be possible to calculate relative sensitivity factors in the absence of reference materials.     

Perspectives in the development of the theory of spark-source and laser-plasma source mass-spectrometry

The processes of substance evaporation and atom ionization under different conditions of spark discharge or laser radiation are considered. It is shown that the dependence of the relative sensitivity coefficients on the properties of an element can be presented as the product of two exponents with parameters proportional to the atomization energies and first ionization potentials of the element. Differences in matrix composition and conditions influencing a sample in the ion source are considered by means of introducing two fitting parameters-atomization and ionization "temperatures"-into these exponents. Experiments carried out with the help of mass-spectrometers with spark and laser ion sources have corroborated the validity of the suggested quasi-equilibrium model and shown the possibility of its application for the improvement of the accuracy of analysis without use of standards as well as for checking the stability of experimental conditions in the process of analysis with standard samples.     

Validation of the sulphur concentration of selected iron-base NBS standard reference materials by isotope-dilution spark-source mass-spectrometry

An isotope-dilution spark-source mass-spectrometric procedure has been developed for the accurate determination of sulphur in iron-base alloys. Dissolution in a sealed tube is used to prevent volatilization losses and to effect isotope equilibration. Application of this technique to the re-analysis of existing NBS Standard Reference Materials yields results that are generally in good agreement with the certified values.     

Parameters of models and conditional sensitivity coefficients of radial distribution functions for water calculated by molecular dynamics data

The influence of parameters of rigid models of the 12-6-1 type on the properties calculated in computer experiments, viz., radial distribution functions and internal energy, was studied by the method of step-by-step transform of the water models supplemented by calculations of conditional sensitivity coefficients.     

Modification in the surface composition of sparked aluminium electrodes and its relation to relative sensitivity factors in spark-source mass spectrometry

Secondary ion mass spectrometry (SIMS) was used to measure in-depth distributions of a number of minor elements in the surfaces of aluminium electrodes after sparking in a spark source mass spectrometer (SSMS). The surface composition of the sparked electrodes was found to differ from that of the bulk. The secondary ion intensity ratios in the sparked surface and in the bulk, both normalized to the corresponding Fe⁺ signal, agreed remarkably well with relative sensitivity factors (relative to Fe), which were experimentally determined for SSMS using homogeneous A1 standard reference materials.

This suggests that differences in relative sensitivity factors are, at least to some extent, caused by a different behaviour of the corresponding constituents in the electrode surface during sparking.     

Comparison of ab initio calculated and experimental methyl-top moments of inertia

The methyl-top moments of inertia and planar moments of inertia of a large number of compounds have been obtained from rotational spectroscopic data and are compared with the corresponding quantities obtained from ab initio geometries. Ab initio geometry refinements have been performed with the 4-21G basis set using standard gradient techniques. High correlation is found between the spectroscopic and calculated values, indicating the possibility of using experimental methyl-top moments of inertia as a source of structural information on methyl groups.     

Relative sensitivity of rare earth elements in spark-source mass spectrometry

A method for calculating the relative sensitivity factors for the rare earth elements in geological material is outlined. A close correlation is found between the relative sensitivity factors calculated and isotopic mass and the first ionization potential for the elements. The points are grouped in the vicinity of a regression line, which may be used to determine the relative sensitivity factors for all the rare earth elements.     

Comparison of calculated and experimental FTIR spectra of specifically labeled ubiquinones

Density functional theory has been used to calculate harmonic vibrational frequencies and intensities of unlabeled and labeled ubiquinone-1 in both the gas phase and in solution (CCl₄). Calculations were undertaken using the B3LYP functional and the 6-31G+(d) basis set. Calculations using larger basis sets did not significantly alter the calculated spectra. Calculations for ubiquinone-2, -3, -6 or -8 gave similar results.Calculations show that eight ubiquinone-1 conformations, which differ only in the orientation of their methoxy groups, are likely to coexist in solution at room temperature. The calculated infrared spectra for these eight conformations vary considerably. However, by averaging the Boltzmann weighted spectra for the eight conformers, composite spectra are calculated that successfully model both the frequency and intensity information inherent in the experimental FTIR spectra obtained for both unlabeled and labeled ubiquinones in solution.The calculated spectra presented here provide a robust foundation from which to consider and assess future modeling of the vibrational properties of ubiquinones embedded in protein complexes.     

Comparison between experimental and calculated results on the decomposition of chemically activated alcohols

The life times of chemically activated alcohols have been determined using the high-pressure unimolecular rate parameters for thermal decomposition of alcohols from shocktube studies and RRKM calculations. They are compared with literature numbers (from insertion of 0(¹D) into hydrocarbons). It is suggested that in some cases singlet oxygen carries excess energy into the hydrocarbon. The consequences of such an assumption are explored and discrepancies with previously published conclusions discussed.     

Comparison of experimental and calculated peak shapes for three cylindrical geometry FAIMS prototypes of differing electrode diameters

High-field asymmetric waveform ion mobility spectrometry (FAIMS) separates ions at atmospheric pressure and room temperature based on the difference of the mobility of ions in strong electric fields and weak electric fields. This field-dependent mobility of an ion is reflected in the compensation voltage (CV) at which the ion is transmitted through FAIMS, at a given asymmetric waveform dispersion voltage (DV). Experimental CV, relative peak ion intensity, and peak width data were compared for three FAIMS prototypes with concentric cylindrical electrodes having inner/outer electrode radii of: (1) 0.4/0.6 cm, (2) 0.8/1.0 cm, and (3) 1.2/1.4 cm. The annular analyzer space was 0.2 cm wide in each case. A finite-difference numerical computation method is described for evaluation of peak shapes and widths in a CV spectrum collected using cylindrical geometry FAIMS devices. Simulation of the radial distribution of the ion density in the FAIMS analyzer is based upon calculation of diffusion, electric fields, and the electric fields introduced by coulombic ion-ion repulsion. Excellent agreement between experimental and calculated peak shapes were obtained for electrodes of wide diameter and for ions transmitted at low CV.     

General therodynamic identities for sensitivity coefficients

Expressions are obtained for the sensitivity coefficientsn _i /Y of the equilibrium state of a homogeneous multicomponent system in which chemical reactions occur, and in which ideal behavior of the components isnot assumed;n _i is the equilibrium amount of theith chemical species, andY is a parameter influencing the equilibrium. These therodynamic identities represent generalizations of the results of the same kind, recently reported for systems with ideal behavior [I. Gutman, I. Fishtik and I. Nagypál, J. Math. Chem. 16 (1994) 229]. Also in the most general case,n _i /Y is found to be equal to the sum of contributions originating from certain special equilibria, previously named as Hessian response reactions.