Isotope ratio determination of uranium by optical emission spectroscopy on a laser-produced plasma - basic investigations and analytical results

We report in this paper, the first determination of the isotope ratio (238/235) in an uranium sample by optical emission spectroscopy on a laser-produced plasma at reduced pressure (2.67 Pa). Investigations aimed at developing a new application of laser ablation for analytical isotope control of uranium are presented. Optimized experimental conditions allow one to obtain atomic emission spectra characterized by the narrowest possible line widths of the order of 0.01 nm for the investigated transition UII 424.437 nm. We show the possibility to achieve a relative precision in the range of 5% for an enrichment of 3.5% ²³⁵U. The influence of different relevant plasma parameters on the measured line width is discussed.     

微量元素铬的分析方法研究进展

就国内外近年来对食品，药物，环境等样品中铬元素的分析方法研究进展进行了综述。主要有分光光度法，原子吸收分光光度法，荧光分析法，化学发光法，电化学分析法，电感耦合等离子体发射光谱法，色谱法，质子诱发X－射线分析法和共振瑞利散射法。     

Optimization of instrumental variables in flame atomic absorption spectrometry

The optimization of flame atomic absorption instrumental variables such as hollow-cathode lamp current, slit width, slit height, flame type and stoichiometry, burner position, resonance line, and integration time for best precision or signal-to-noise ratio is discussed. Because different types of noise are limiting in different absorbance regions, optimum values of instrumental variables can vary with the absorbance measured.     

Some causes of bending of analytical curves in atomic emission flame spectrometry

Factors affecting the shape of analytical curves in atomic emission flame spectrometry are discussed. Equations are presented by which the effect on the analytical curve of self-absorption, ionization, compound formation, variation in solution flow rate and atomization efficiency, entrance optics, and multiple spectral lines can be considered quantitatively. Theoretical and experimental curves are compared for Na introduced as aqueous NaCI solution into H₂/air, H₂/O₂, and C₂H₂/O₂ flames. The portion dealing with the effect of ionization, compound formation, and variation in solution flow rate and atomization efficiency on the atomic concentration in the flame applies as well to atomic absorption and atomic fluorescence flame spectrometry.     

Atomic absorption with ultracold atoms

Recent advances in laser-atom cooling techniques and diode-laser technology now allow one to conduct an idealised atomic absorption experiment comprising a sample of ultracold, quasi-stationary absorbing atoms and a source of near-monochromatic resonant light. Under such conditions, the atomic absorption coefficient at line centre is independent of the oscillator strength of the atomic resonance line. This offers the prospect of ‘oscillator-strength-free’ atomic absorption spectroscopy in which the absorption signal is equally large for both strong and weak (closed) transitions of the same wavelength and in which absolute atomic absorption could be performed without knowledge of the oscillator strength. Moreover, the resolution and sensitivity for a given atom density are greatly enhanced, typically by approximately three orders of magnitude (and even more for weak transitions), compared with conventional flame or graphite-furnace atomic absorption. We describe an atomic absorption experiment based on samples of ultracold, laser-cooled caesium atoms and a narrow-bandwidth diode laser source that approximates the idealised conditions for oscillator-strength-free atomic absorption. The absorption measurements are used to determine the number density and temperature (approx. 6 μK) of the sample of ultracold atoms. Some of the technical obstacles that would have to be overcome before samples of ultracold atoms and diode laser sources could be used in analytical atomic absorption spectroscopy are discussed.     

Einflu\ der spektralen Bandbreite des Monochromators auf die Empfindlichkeit von atomabsorptiometrischen Bestimmungen

Zusammenfassung Bei der atomabsorptiometrischen Bestimmung vieler Elemente, wie z.B. Ni, Fe und Pd, werden die anfÄngliche Neigung und die Krümmung der Eichkurven durch die spektrale Bandbreite des Monochromators stark beeinflu\t, wenn dieser nicht oder schwach absorbierte Linien von der Resonanzlinie nicht zu trennen vermag. Die AbhÄngigkeit der optischen Dichte von der Konzentration und der spektralen Bandbreite wird mit Hilfe einer Funktion beschrieben, welche die Konzentration, die spektrale Bandbreite, die relative IntensitÄt der von der spektralen Strahlungsquelle emittierten Linien, die Absorptionskoeffizienten, sowie die AbstÄnde der Störlinien von der Resonanzlinie als Variablen enthÄlt. Ein Verfahren wird diskutiert, welches auf der Registrierung von Emissionsspektren in engen Bereichen an beiden Seiten der betreffenden Resonanzlinie beruht und alle Daten für die letztgenannten drei Grö\en liefert. Das Verfahren gibt zudem nützliche Informationen über den Zustand der Energiequelle.

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Influence of the spectral band width of the monochromator upon the sensitivity of determinations by atomic absorption spectrometry

Summary In determinations of many elements, like Ni, Fe and Pd, by AAS the initial slope and the bending of the calibration curves are strongly affected by the spectral band width of the monochromator, if that cannot separate the resonance line from other not or weakly absorbed lines. The dependence of the optical density on the concentration and spectral band width is described by a function with the variables: concentration, spectral band width, relative intensities of lines emitted by the spectral source, absorption coefficients and the distances of disturbing lines from the resonance line. A procedure is discussed, which is based on the registration of emission spectra in a small spectral range on both sides of the resonance line in question and provides the data for the three quantities mentioned last. The procedure provides also useful information about the condition of the spectral source.

Der Eidg. Stiftung zur Förderung Schweizerischer Volkswirtschaft durch wissenschaftliche Forschung danken wir für die finanzielle Unterstützung.     

Calculation of non-linearities of the calibration curves in atomic absorption flame spectroscopy

The deviations from the linear relationship between absorbance and concentration in atomic absorption measurements are calculated. Besides the chemical reactions there are four groups of interferences: (a) profiles of emission- and absorption lines (b) hyperfine structure (c) optics around the flame (d) non resonant light detected by the amplifier due to the optical arrangement and/or resolution of the monochromator.

The calculations show that curvature of experimental curves as obtained by apparatus for atomic absorption spectroscopy is caused partly by optical compromises and partly by the emission profile of the source. With a narrow simple emission line profile of the source and a precision monochromator a linear relationship within a few percent is possible up to 95 per cent absorption in a flame at atmospheric pressure.     

Atomic physics and atomic spectroscopy: mother and daughter?

In Part 1 the roots of analytical atomic emission (AES), absorption (AAS), fluorescence (AFS), optogalvanic (OG) and forward-scattering (FS) spectroscopy in atomic physics are exposed. The essential differences between FS and AAS or AFS are stressed. The links of plasma-source mass-spectrometry with atomic spectroscopy and with flame ionization research are also indicated. Part 2 deals with various aspects of the continual interrelation between atomic physics and atomic spectroscopy. The usage of AAS in atomic physics is exemplified by shock-tube experiments on the oxidation of Cr atoms and the curve-of-growth of the Cr resonance lines in argon. Examples of the usage of AFS in physical experiments are given that relate to the collisional mixing of Zeeman substates and the far-wing profiles of the collisionally broadened Na-D lines. Other aspects of this interrelation are discussed that relate to the sources of atomization and excitation, to the detection or measuring techniques, and to the research or development of analytical methods and sources. In Part 3 the revival of AES and the prospects of some laser-based atomic spectroscopies are summarized, whereas a further exploitation of anomalous dispersion in analytical atomic spectroscopy is suggested. General conclusions and exhortations are collated in Part 4.     

Unusual calibration curves observed for iron using high-resolution continuum source graphite furnace atomic absorption spectrometry

The simultaneous determination of cadmium and iron in plant and soil samples has been investigated using high-resolution continuum source graphite furnace atomic absorption spectrometry. The primary cadmium resonance line at 228.802 nm and an adjacent secondary iron line at 228.726 nm, which is within the spectral interval covered by the charge-coupled device (CCD) array detector, have been used for the investigations. Due to the very high iron content in most of the soil samples the possibility has been investigated to reduce the sensitivity and extend the working range by using side pixels for measurement at the line wings instead of the line core. It has been found that the calibration curves measured at all the analytically useful pixels of this line consisted of two linear parts with distinctly different slopes. This effect has been independent of the positioning of the wavelength, i.e., if the Cd line or the Fe line was in the center of the CCD array. The most likely explanation for this unusual behavior is a significant difference between the instrument width Δλ_Instr and the absorption line width Δλ_Abs, which is quite pronounced in the case of Fe. Using both parts of the calibration curves and simultaneous measurement at the line center and at the wings made it possible to extend the working range for the iron determination to more than three orders of magnitude.     

Influence of pressure on the determination of palladium by graphite furnace atomic absorption spectrometry using resonance and non-resonance lines

Atomization under pressure considerably influences the absolute and relative sensitivities of resonance and non-resonace lines. Whereas for resonance lines the peak height and area senstitivities decrease with increasing pressure, for non-resonance lines the sensitivity initially increases probably because the increase of the temperature of the atomic vapor compensates for the Lorentz broadening and the red shift. At higher pressures probably absorption line broadening and red shift effect become predominant so that the sensitivity of the non-resonance lines becomes poorer. In spite of this the relative sensitivity of the non-resonance lines as compared to the resonance lines under the same conditions. improves steadily with increasing pressure. It is possible that the absorption profiles of the resonance and the non-resonance lines are affected differently by pressure. The peak characterization times differ considerably for the resonance and non-resonance lines. Calibration curves become more linear with increasing pressure. The improvement is more pronounced for the resonance line.     

Tungsten devices in analytical atomic spectrometry

Tungsten devices have been employed in analytical atomic spectrometry for approximately 30 years. Most of these atomizers can be electrically heated up to 3000 °C at very high heating rates, with a simple power supply. Usually, a tungsten device is employed in one of two modes: as an electrothermal atomizer with which the sample vapor is probed directly, or as an electrothermal vaporizer, which produces a sample aerosol that is then carried to a separate atomizer for analysis. Tungsten devices may take various physical shapes: tubes, cups, boats, ribbons, wires, filaments, coils and loops. Most of these orientations have been applied to many analytical techniques, such as atomic absorption spectrometry, atomic emission spectrometry, atomic fluorescence spectrometry, laser excited atomic fluorescence spectrometry, metastable transfer emission spectroscopy, inductively coupled plasma optical emission spectrometry, inductively coupled plasma mass spectrometry and microwave plasma atomic spectrometry. The analytical figures of merit and the practical applications reported for these techniques are reviewed. Atomization mechanisms reported for tungsten atomizers are also briefly summarized. In addition, less common applications of tungsten devices are discussed, including analyte preconcentration by adsorption or electrodeposition and electrothermal separation of analytes prior to analysis. Tungsten atomization devices continue to provide simple, versatile alternatives for analytical atomic spectrometry.     

Gas-Phase Sample Introduction Techniques in Plasma Atomic Emission Spectrometry

Clearly, the introduction of sample materials in the gas phase is an ideal technique for analytical atomic spectroscopy, i.e., atomic absorption, atomic emission and atomic fluorescence spectrometry.     

Analytical performance of high-voltage neon plasma in glow discharge optical emission spectrometry

In a high-voltage Ne glow discharge plasma (Ne-GDP), calibration factors as well as the limit of determination were compared between atomic resonance lines and singly-ionized lines of copper and aluminium in optical emission spectrometry. These elements have intense ionic lines which are excited by resonance charge-transfer collisions of Ne ions. The ionic lines gave better detection sensitivity in the Ne-GDP, whereas the atomic resonance lines were commonly employed as analytical lines in the other plasma sources such as Ar-GDP and ICP. The limit of determination was 1.3 × 10^–3 mass % for the Cu II 248.58 nm line and 1.0 × 10^–3 mass % Al for the Al II 358.66 nm line at a discharge parameter of 1.60 kV/36 mA.     

Einsatz von rechenanlagen in der emissionsspektrochemie für aufstellung,bewertung und linearisierung der analytischen eichgeradenThe use of computers in emission spectrometry for the establishment,evaluation and linearization of analytical calibration curves

(The use of computers in emission spectrometry for the establishment, evaluation and linearization of analytical calibration curves)The problems of establishing optimum linear calibration lines for atomic emission spectrometry are discussed, with emphasis on use of photographic recording techniques. The calculation procedure, which is based on the least-squares method, generates additional statistical values which permit the linearity to be checked. As the desired linearity is not always achieved at the first attempt, the process is repeated after unreliable input data have been removed.     

LPDA技术在石墨炉原子吸收光谱分析中的应用研究——Ⅱ、一种新的背景校正方法

本文报道的背景校正方法,利用了测量锐线光源辐射谱线轮廓上不同波长位置相应的吸收系数进行背景校正,是作者在利用LPDA作为光电检测系统进行AA研究工作中提出来的。文章论述了方法的基本原理和作者所做的实验研究,7个元素的实验数据证明了方法的正确性。利用这种方法还可以观察原子吸收线与原子发射线之间中心波长的位移现象。     

Line selection and interference correction for the analysis of tungsten alloy by inductively coupled plasma atomic emission spectrometry

A method for the analysis of tungsten alloy to determine selected elements using inductively coupled plasma atomic emission spectroscopy is described, with emphasis on line selection and spectral interference. The spectral interference coefficients were calculated for the spectral lines of selected major and trace elements. These values were used to select analytical lines and to calibrate concentrtions of the analytes. The detection limits of the elements for this method were determined and compared with those obtained by flame atomic absorption spectrometry and direct current carbon are emission spectrometry. The results indicated that the detection limits for all of the elements determined by the proposed method are significantly better than those obtained by other techniques. In this study, the analytical reliability of the proposed method was estimated by comparison of the analytical data for the two types of tungsten alloys produced by the Korean Tungsten Company with those obtained by the matrix matching method and the results indicated that the accuracy of multi-element analysis is satisfactory.     

Furnace atomization plasma emission spectrometry with He/Ar mixed gas plasmas

The influence of plasma gas composition on the operating and analytical characteristics of a furnace atomization plasma emission source (FAPES) is presented. He I and Ar I excitation temperatures increase 30% in the mixed gas plasmas whereas argon ion excitation temperatures decrease from 33 000 K to 26 000 K in the presence of He. Collisional exchange of internal energy between excited states of Ar and He accounts for these changes. Average analyte ionization temperatures (for Cr, Mn, Mg, Co, Fe, Cd and Zn), derived from the relative emission intensities of their ionic and atomic lines in a 40-MHz 50-W plasma, increase from 5270 K to 6740 K with the addition of Ar to He. Ionic line intensities increase from 10-fold (Mn) to 40-fold (Cd, Zn) with addition of Ar to the plasma while atomic line intensities increase only twofold. Limits of detection remain substantially unaltered for atomic transitions due to increased noise but are improved twofold (Cd) to 24-fold (Mn) for ionic transitions. The analytical advantages and disadvantages of mixed gas plasmas are discussed. The Ne I excitation temperature at 40 MHz and 50 W was determined to be 4330±80 K.     

Investigation of chemical modifiers for phosphorus in a graphite furnace using high-resolution continuum source atomic absorption spectrometry

Phosphorus is not one of the elements that are typically determined by atomic absorption spectrometry, but this technique nevertheless offers several advantages that make it attractive, such as the relatively great freedom from interferences. As the main resonance lines for phosphorus are in the vacuum–ultraviolet, inaccessible by conventional atomic absorption spectrometry equipment, L´vov and Khartsyzov proposed to use the non-resonance doublet at 213.5 / 213.6 nm. Later it turned out that with conventional equipment it is necessary to use a chemical modifier in order to get reasonable sensitivity, and lanthanum was the first one suggested for that purpose. In the following years more than 30 modifiers have been proposed for the determination of this element, and there is no consensus about the best one. In this work high-resolution continuum source atomic absorption spectrometry has been used to investigate the determination of phosphorus without a modifier and with the addition of selected modifiers of very different nature, including the originally recommended lanthanum modifier, several palladium-based modifiers and sodium fluoride. As high-resolution continuum source atomic absorption spectrometry is revealing the spectral environment of the analytical line at high resolution, it became obvious that without the addition of a modifier essentially no atomic phosphorus is formed, even at 2700 °C. The absorption measured with line source atomic absorption spectrometry in this case is due to the PO molecule, the spectrum of which is overlapping with the atomic line. Palladium, with or without the addition of calcium or ascorbic acid, was found to be the only modifier to produce almost exclusively atomic phosphorus. Lanthanum and particularly sodium fluoride produced a mixture of P and PO, depending on the atomization temperature. This fact can explain at least some of the discrepancies found in the literature and some of the phenomena observed in the determination of phosphorus using line source atomic absorption spectrometry.     

Multielement atomic absorption analysis using Hadamard transform spectroscopy with a new computation and superposition procedure

The application of Hadamard transform spectroscopy (HTS) to analytical atomic spectroscopy has been investigated. A theoretical examination of the signal to noise ratio indicates that HTS offers a slight multiplex advantage over single slit scanning of the spectrum for the measurement of intense lines, as in atomic absorption, but is disadvantageous for measuring small signals in atomic emission and fluorescence. Using a simple HT spectrometer Mg and Pb were determined simultaneously by flame atomic absorption spectrometry. Sensitivities similar to those of conventional systems were obtained but, owing to instrumental imperfections and a short data collection time, detection limits were worse. Optimum system performance was obtained when the mask interval width was equal to the width of the image of the spectrometer entrance slit. Greater spectral detail was revealed by superposition of a set of computed spectra in which the starting point of each spectrum was displaced from the others by a distance less than the interval width of the Hadamard mask. This approach gave improved spectra without increased instrumental complexity.     

Investigation of artifacts caused by deuterium background correction in the determination of phosphorus by electrothermal atomization using high-resolution continuum source atomic absorption spectrometry

The artifacts created in the measurement of phosphorus at the 213.6-nm non-resonance line by electrothermal atomic absorption spectrometry using line source atomic absorption spectrometry (LS AAS) and deuterium lamp background correction (D₂ BC) have been investigated using high-resolution continuum source atomic absorption spectrometry (HR-CS AAS). The absorbance signals and the analytical curves obtained by LS AAS without and with D₂ BC, and with HR-CS AAS without and with automatic correction for continuous background absorption, and also with least-squares background correction for molecular absorption with rotational fine structure were compared. The molecular absorption due to the suboxide PO that exhibits pronounced fine structure could not be corrected by the D₂ BC system, causing significant overcorrection. Among the investigated chemical modifiers, NaF, La, Pd and Pd + Ca, the Pd modifier resulted in the best agreement of the results obtained with LS AAS and HR-CS AAS. However, a 15% to 100% higher sensitivity, expressed as slope of the analytical curve, was obtained for LS AAS compared to HR-CS AAS, depending on the modifier. Although no final proof could be found, the most likely explanation is that this artifact is caused by a yet unidentified phosphorus species that causes a spectrally continuous absorption, which is corrected without problems by HR-CS AAS, but which is not recognized and corrected by the D₂ BC system of LS AAS.