Acta Part Research Articles

DensMat: fully time-resolved simulation of two-step pulsed laser excitation of atoms in highly collisional media

A program that simulates and displays the level populations of atomic systems exposed to dual-wavelength (i.e. two-colour) pulsed laser excitation in highly collisional media (such as flames and plasmas) has been developed. The program is based upon a previously published fully time-dependent density-matrix model that describes step-wise excitations of atoms with degenerate states under collision-dominated conditions, and which thus goes beyond the rate-equations formalism. This model can predict such phenomena as Rabi flopping and a.c.-Stark splitting, shifting and broadening. The program can be used as a prediction tool for laser-enhanced ionization, laser-induced fluorescence, fluorescence dip spectroscopy and other two-colour laser-based spectroscopic experiments. The program provides the user with a flexible four-level atomic system, configurable as a one- or two-step excitation ladder, along with an ionization continuum and non-laser-connected level(s) that may act as trap(s) or metastable level(s). Parameters such as level degeneracy, collisional rates and laser pulse widths, shapes, wavelengths, intensities and bandwidths are accessible to the user. The program can display both the time development of the level populations and also level populations versus laser wavelength. This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hardcopy text is accompanied by a disk containing the program DensMat, an associated on-line help file and manual, an installation program, and data files pertaining to the examples illustrated in this article. The program runs under Windows 3.1 on an IBM-compatible computer.

IDAS: a Windows based software package for cluster analysis

This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hardcopy text, comprising the main article and one appendix, is accompanied by two installation diskettes with the software package and data files. The main article discusses the chemometric aspects of the package and explains its purpose. The IDAS software package combines three cluster analysis methods (hierarchical, non-hierarchical and fuzzy) and runs under MS Windows. Modified algorithms for non-hierarchical and fuzzy clusterings are described. The interpretation of the clustering results is facilitated by the extensive use of different types of graph. New approaches to the graphical representation of the results of fuzzy clustering are proposed. Two data sets, the Iris data by Fisher and a data set on the chemical composition of tea, are used to demonstrate the capabilities of the software.

Erratum to “SERS studies of methylviologen on silver sol and the effect of halide ions” [Spectrochimica Acta Part A 51 (1995) 717

Erratum to “SERS studies of methylviologen on silver sol and the effect of halide ions” [Spectrochimica Acta Part A 51 (1995) 717

Capillary Blood Collection by Paper for Lead Analysis by Graphite Furnace Atomic Absorption Spectrometry

A lead testing method is described that utilizes fingerstick capillary blood collected on Schleicher & Schuell 903 paper. The dried blood is eluted by treatment with 5% v/v nitric acid-0.75% v/v Triton X-100 to yield an aqueous solution for analysis, so that neither burning nor acid digestion of the paper is needed. Measurement of the lead in the eluted solution is done by graphite furnace atomic absorption spectrometry (GFAAS). The proposed method is not quantitative and must be used only for screening purposes. An initial comparison was made with venipuncture samples assayed for blood lead by a revised matrix modifier method adapted from Parsons and Slavin ( Spectrochim. Acta Part B, 1993, 48, 925-939). The blood samples were spotted on paper and assayed by the proposed method to give a correlation of r = 0.993 ( n = 39). A parallel study of 100 samples of capillary blood obtained by a fingerstick and corresponding venipuncture samples assayed by a matrix modifier method showed a correlation of r = 0.973 ( n = 100). The ease of transporting samples collected on paper and the relatively more pleasant means of obtaining blood from young children by fingerstick are other advantages. Thus, the proposed method offers another approach to processing blood samples for lead screening by atomic absorption spectrometry.

Mechanism of thermal decomposition of hydrated copper nitrate in vacuo

The general scheme of three-stage thermal decomposition of Cu(NO 3) 2·3H 2O to CuO has been refined based on evolved-gas-analysis data with a quadrupole mass analyzer (Jackson et al., Spectrochim. Acta Part B, 50 (1995) 1423). Quantitative evaluation of the composition of the gaseous products shows that the first stage involves primarily deaquation, and the second stage, primarily denitration of the original hydrated nitrate. The basic nitrate formed in the second stage most probably has the formula Cu(NO 3) 2·3Cu(OH) 2. It has been established that the molecular oxygen observed in the third stage of decomposition is produced by catalytic decomposition of NO 2 on the surface of CuO. The presence of Cu-containing ions in all stages of the process is consistent with the gasification mechanism of thermal decomposition.

Mechanism of thermal decomposition of anhydrous metal nitrates

In the previous paper (Jackson et al., Spectrochim. Acta Part B, 50 (1995) 1423), the gas phase products of the thermal decomposition of anhydrous Ag, Cd and Pb nitrates have been measured by means of quadrupole mass spectrometry. These results are used in this paper to distinguish between two alternative mechanisms for this process, the universally recognized condensation mechanism involving direct production of the solid metal (Ag) or oxide (CdO and PbO) through recrystallization, and the recently proposed gasification mechanism (B.V. L'vov, Mikrochim. Acta II (1991) 299) that includes a primary stage of complete gasification of all decomposition products. Quantitative analysis of the yield of volatile (NO 2 and NO) and non-volatile (M, MO and MNO 3) products into the gas phase has shown the thermal decomposition of all nitrates to proceed in a congruent way. The kinetic parameters of the process, namely, the appearance temperature and the activation energy are in good agreement with the values of these parameters calculated for the gasification mechanism. Based on these findings, and also on a qualitative analysis of some other results, the conclusion is drawn that the thermal decomposition is governed by the gasification mechanism.

Signal processing of transient atomic absorption signals

This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hard copy text is accompanied by a disk with a demonstration version of the simulation program, libraries of electronic and optical component blocks, simulation models, manual, and other files. Absorbance signals for electrothermal atomization atomic absorption spectroscopy (ETA-AAS) were generated digitally and the effect of various types and sources of noise upon the precision of the absorbance measurement was evaluated by numerical calculation. Peak area measurement, peak height measurement, and matched filtering were used for processing these signals. The performance of these three techniques in the presence of various types of noises and the sensitivity of each to small variation in the atomization conditions was calculated. It is demonstrated that significant improvement in signal-to-noise ratios can be realized by application of appropriate signal processing methods. The results also indicate that one of the principal causes for loss of precision could be the variation in the heating characteristics of the furnace.

A LabVIEW ® program for determining electron number density from Stark broadening measurements of the hydrogen-beta line

A useful plasma diagnostic is the measurement of electron number density. One way to accomplish such measurements is to determine the contribution to the broadening of a spectral line due to the Stark effect. To simplify and extend such electron density measurements across computer platforms, a program that calculates electron number density from the Stark-broadened hydrogen-beta line has been written for the LabVIEW ® environment. This program calculates electron number densities from the field strength that would be exerted on a hydrogen atom immersed in a plasma. Using the new program, the electron number density in a glow discharge is calculated for two different operating conditions. Not surprisingly, the results indicate that to increase the current density in the discharge, the source electrodes must be reduced in surface area. This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hardcopy text is accompanied by one disk with an executable program (written for Apple Macintosh), data and text files including a manual.

Comment on “The roles of carbon dioxide and water vapour in warming and cooling the Earth's troposphere” J. Barrett, Spectrochim. Acta part A, 51 (3) (1995) 415

Comment on “The roles of carbon dioxide and water vapour in warming and cooling the Earth's troposphere” J. Barrett, Spectrochim. Acta part A, 51 (3) (1995) 415

Comment on “The roles of carbon dioxide and water vapour in warming and cooling the Earth's troposphere” J. Barrett, Spectrochim. Acta Part A, 51 (3) (1995) 415

Comment on “The roles of carbon dioxide and water vapour in warming and cooling the Earth's troposphere” J. Barrett, Spectrochim. Acta Part A, 51 (3) (1995) 415

Automated simplex optimization for monochromatic imaging inductively coupled plasma atomic emission spectroscopy

This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hardcopy text is accompanied by a diskette with data files and text files with the hardcopy paper in Word for Windows 2.0 and ASCII format, and a disclaimer. The text details the purpose of the work, and the appendix provides essential information for accessing the diskette and using programs and data. An automated simplex optimization program was written in an attempt to relieve the monotonous human effort required to optimize an inductively coupled plasma atomic emission spectroscopic (ICP-AES) instrument. The program controls the operating conditions of a solid-state ICP while a monochromatic imaging spectrometer collects two-dimensional response images. In the work described in this article, four of the most important ICP operating parameters are optimized automatically: radio frequency (rf) power, intermediate Ar flow rate, nebulizer flow rate and sample uptake rate. Optimization of these parameters is based first on the response of the Ca II net signal and, independently, on the response of the Ca II net signal-to-background noise ratio ( S N B ). Since the best height and off-axis positions of the designated response are known from the optimal two-dimensional response image, two spatial parameters are indirectly optimized through use of a CCD camera. Optimal operating conditions are reported for the CA II net signal and Ca II S N B as well as the Mg II Mg I ratio.

Nonlinearity properties of certain rare-earths mixed laser dyes from their refractive indices measurements

This note reports the non-linearity characteristic parameters of certain laser dyes such as rhodamine-B, rhodamine-6G and pyronine-G(y) dissolved in both methyl and ethyl alcohols mixed with some rare-earths. The parameters are taken from the measurement of refractive indices at three different wavelengths ( F = 486.1 nm, d = 589.3 nm and C = 656.3 nm) and used to identify which dye laser liquid has the lowest optical dispersive power among the three investigated. The British Library Document Supply Centre Supplementary Publication No. SUP 13083 contains 7 pages of manuscript. Retrieval information is given on the penultimate page of Spectrochimica Acta Part A.

My memory of spectroscopy in the U.S.A.: an exciting era of atomic emission, atomic absorption and atomic fluorescence

In order to pay tribute in the special issue of Spectrochimica Acta Part B for Professor J.D. winefordner, this author looked back at the most exciting era of spectrochemical analysis, which started in 1955, during which atomic absorption, atomic emission as well as atomic fluorescence made remarkable development. Coincidentally this author made a stay in the U.S.A. as a Fulbright Exchange Scholar from Japan. My recollections start from the cathode layer excitation of Dr L.W. strock, Zn enzymes of Dr B. L. vallee, and continue to the so-called “single atom” detection by atomic fluorescence of Prof. winefordner.

Contributions to computer-aided interpretation of ion sputtering depth profiling

To evade some of the problems that restrict the quantification of sputtering depth profiling, i.e. the conversion of measured signal intensity vs sputtering time profiles into the concentration vs depth scale in the case of changing sputtering rate with depth, algorithms and computer programs are presented for modelling the intensity vs time profile by computer simulation of the measuring process. Required are only rough a priori information on the sample type under investigation, e.g. implanted material or layer systems, some knowledge of the actual sputtering conditions and basic assumptions on origin, transmission and registration of the analytical signals. The modelled profile may be adapted to the measured one by interactive, stepwise variation of parameters assumed to be important. For scanned ion beams, procedures for efficient estimation of the actual ion current density and of the changing sputtering rate with depth are given too. All calculations can be performed at a desk using any IBM compatible personal computer. Owing to its modular structure, the program may be easily extended and completed according to model refinements by users. Agreement between computed and measured profiles indicates that the a priori assumptions on the true depth profile were correct in all probability. Otherwise, in most cases, further experiments have to be performed in order to decide between experimental artefacts and material-inherent deviations considering also atomic mixing, radiation enhanced diffusion, preferential sputtering and similar effects. Moreover, the quantitative relations between sputtering conditions and crater shape obtainable by the model can support optimization of the measuring conditions particularly with respect to depth resolution. At last, the procedures and algorithms given here are a contribution to the final aim of direct quantification of the results of sputtering depth profiling. This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hard copy text is accompanied by three disks with executable programs, source code files, data files and text files. The manual and tutorial text files include material that is useful for learning the effective handling of the program and for program extension by user-written program parts.

Revised, fast, flexible algorithms for determination of electron number densities in plasma discharges

This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hard copy text is accompanied by a disk with two electron number density ( n e) calculation programs written in Turbo Basic (NNE.EXE) and C language (NE.EXE), data mes ( ∗.DAT), a text file (NE.WP) with the hard copy paper in WordPerfect 5.1 and a text file (README) for the introduction of the data files and programs. The theoretical aspects and applications of NNE.EXE and NE.EXE are described in the main article for three plasmas having a wide range of electron number density (4 × 10 13 to 1 × 10 17 cm −3). The descriptions of the procedure, data format, and hardware requirements can be found in the Appendix and the README file. The determination of n e. is accomplished by least-squares fitting of the entire emission profile or the wing portions of the emission profile of the H β line (486.13 nm) to the theoretical Stark broadened profiles, compiled at electron temperature 2500, 5000, 10000 and 20000 K. This approach can reduce errors in the determination of n e owing to the structural dip in the center of the Stark profiles depending on n e value. The curve-fitting routine employs an interval-halving algorithm to produce new interpolated Stark profiles, reduces number of iterations and time required for calculation, and allows the calculation of n e to the limits set by instrument spectral resolution and the availability of theoretical spectral data. Additionally, each program provides graphic displays allowing the reader to observe the interpolated Stark profiles, the fitting process, and magnitude of residuals during the course of calculation, and the effects of plasma temperatures and spectral resolution on the estimation of n e. In addition to H β, theoretical profiles also are included for H α and H γ to illustrate the suitability and drawbacks of these lines for n e estimation. These programs are extended versions of a program reported earlier in Spectrochimica Acta 44B, 175 (1989).

The Kalman filter approach to inductively coupled plasma atomic emission spectrometry

This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hardcopy text, comprising the main article and two appendices, is accompanied by a disk containing the compiled program, a reference manual and data files. The work deals with data handling in inductively coupled plasma atomic emission spectrometry (ICP-AES). With this technique, the analyte signal is superimposed on a background signal. When separating the signals by manual or automated three-point background correction, there are many instances in which the data reduction fails. Based on scans recorded in a fast-scanning mode and on a library of pure-component scans, the Kaiman filter approach models the emission in the spectral window (about 100 pm) of the analyte and mathematically solves the problem of background correction. By using a criterion-based algorithm to correct for optical instability, the uncertainty in the determination of the interferent line signal is eliminated. Therefore, the present filter implementation yields more accurate and precise results, especially in the case of line overlap. The Kalman filter Approach to Atomic Spectrometry (KAAS) software automatically processes Perkin-Elmer Plasma 1000 2000 text files, but can also handle ASCII data files. Practical and comprehensive examples are given to evoke the “Kalman filter feeling” in the crucial step of creating the emission model.

Uranium spectra in the ICP

Uranium spectra have been studied by inductively coupled plasma atomic emission spectroscopy (ICP-AES). In total, 8361 uranium lines were observed in the wavelength range of 235–500 nm. This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hard copy text is accompanied by a disk with data files and text files for an IBM-compatible computer. The main article discusses the scientific aspects of the subject and explains the purpose of the data files.

The effect of sample matrix on electron density, electron temperature and gas temperature in the argon inductively coupled plasma examined by Thomson and Rayleigh scattering

Spatially-resolved electron temperature ( T e), electron number density ( n e) and gas-kinetic temperature ( T g) maps of the inductively coupled plasma (ICP) have been obtained for two central-gas flow rates, four heights above the load coil (ALC) and in the presence and absence of interferants with a wide range of first ionization potentials. The radial profiles demonstrate how the directly measured fundamental parameters n e T e and T g can be significantly enhanced and/or depressed with added interferent, depending upon plasma operating conditions and observation region. In general, the magnitude of n e, and T e change is found to be an inverse function of interferent ionization potential; furthermore, n e enhancements in the central channel might be the result of electron redistribution from high to low electron density regions rather than from ionization of the matrix. The large measured increases in n e cannot be attributed solely to matrix ionization, especially when measurement uncertainties and the probable over-estimation in calculated n e, enhancements are taken into account. Changes in n e and T e have been correlated with axial Ca atom and ion emission profiles. A brief review of the mechanisms most likely involved in interelement matrix interferences is given within the context of the present study. This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hardcopy text is accompanied by a disk for the Macintosh computer with data files stored in ASCII format. The main article discusses the scientific aspects of the subject and gives an interpretation of the results contained in the data files.

Tomographically resolved ionization temperatures and electron densities in the inductively coupled plasma determined by the line-to-continuum method

This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hardcopy text is accompanied by three disks with data files with the hardcopy paper in Word 5.0 and ASCII format, and a disclaimer. The text details the purpose of the work and the structure of the three-dimensional Ar ionization temperature and electron number density data files. The line-to-continuum method was used to evaluate the spatial distribution of Ar ionization temperatures, T ion, and electron number densities, n e, within a dry Ar inductively coupled plasma (ICP). The emission measurements were spatially resolved in three dimensions by reconstruction algorithms for computed tomography. The 40.68 MHz Ar ICP was operated at applied r.f. power levels of 0.75 and 1.0 kW. The reconstructed distributions of Ar I line emission (430.0 nm) and continuum emission (428.6 nm) show good reproducibility over a series of five replicate runs. Argon ionization temperatures remain within a 6500–8500 K range throughout the continuum-emission cone of the plasma. Deviations from this temperature range occur in the central channel and around the outer edge of the plasma. Low in the plasma, the central-channel T ion is cooler than 6000 K. Along the outer edge of the plasma, the line-to-continuum ratio becomes small; this low ratio results in erroneously high temperatures (> 12000 K). The errors in T ion appear to be due to reproducible artifacts in the reconstruction process that lead to low Ar I line-emission readings along the outer edge of the plasma. Electron densities show a maximum of 8.5 × 10 14 cm −3 and 1.2 × 10 15 cm −3 at 0.75 and 1.0 kW, respectively. Electron number densities were much better behaved than T ion due to their dependence on the square-root of continuum measurements and only the fourth-root of T ion.

Spectral interferences in the determination of traces of scandium, yttrium and rare earth elements in “pure” rare earth matrices by inductively coupled plasma atomic emission spectrometry—II: Praseodymium and samarium

This paper is the second part of a series of papers dealing with mutual spectral interferences of rare earth elements (REEs) in inductively coupled plasma atomic emission spectrometry (ICP-AES). The present article covers: (a) the spectral data of praseodymium and samarium interferents for 200 pm wide windows centred (± 100 pm) about prominent lines of scandium, yttrium and REEs; (b) the data base of Q values for line interference ( Q 1) and Q values for (wing) background interference ( Q w); and (c) the detection limits measured by using the “true detection limit” criterion as proposed by Boumans and vrakking [ Spectrochim. Acta 42B, 819 (1987); 43B, 69 (1988)]. The lines with the lowest values of true detection limits for praseodymium and samarium matrices were chosen for analysis. This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hardcopy text is accompanied by a disk with data and text files. The data files comprise in particular the tabular material of this article in electronic form.