Spectroscopic study of atomization processes and inter-element effects on the flame emission of chromium and iron in an air—acetylene flame

Emission spectroscopy is applied for characterization of reactions occurring in air—acetylene flames normally used for atomic absorption spectrometry. Inter-element effects on the emissions of chromium and iron are discussed. Two atomic emission lines with different upper energies and a molecular emission line of the diatomic oxide MO are compared for determination of the excitation temperature and the degree of atomization in fuel-rich and lean flames. The reductive power of the fuel-rich flame is essential for atomization of chromium salts. Inter-element effects by iron can be attributed to the formation of refractory oxides, and to mutual catalytic oxidation.     

Comparison of atomic fluorescence power efficiencies for the helium-oxygen-acetylene and air-acetylene flames

Power efficiencies for five elements have been measured for the helium-oxygen-acetylene and air-acetylene flames. The increased power efficiencies found in this study for the helium-diluted flame, coupled with its enhanced atom-formation capabilities, suggest that lower atomic fluorescence detection limits should exist. However, in a comparison study with an air-acetylene flame using identical experimental conditions, a decreased atomic fluorescence signal-to-noise ratio was found for most elements in the helium-diluted flame. This decrease is ascribed to greater background emission noise in the hotter helium-diluted flame and decreased nebulization efficiency caused by the low density of the helium-containing nebulizer gas. A comparison of flame emission detection limits for the two flames confirms the increased sensitivity of the hotter helium-oxygen-acetylene flame, despite its lower nebulization efficiency.     

Comparison of the helium/oxygen/acetylene and air/acetylene flames as atom sources for continuum-source atomic fluorescence spectrometry

The helium/oxygen/acetylene flame is compared to the more widely used air/acetylene flame for its utility as an atom cell for atomic fluorescence spectrometry. Nearly identical experimental arrangements were used for both flames in order to make the comparison valid. With a continuum source used for excitation, fluorescence detection limits in the helium/oxygen/acetylene flame were between 13 and 60 times better (lower) than those determined for the same eight elements in the air/acetylene flame. The improved detection limits are attributable mainly to the higher temperature, increased thermal conductivity and lower quenching in the helium flame. Fluorescence background spectra were obtained for both flames over the wavelength range 185–650 nm, and showed the helium flame to have slightly smaller background fluctuations, but a much larger background because of the more favorable fluorescence conditions in the flame.     

Atomic fluorescence and atomic emission measurements with an image dissector echelle spectrometer

This paper deals with the investigation of an image dissector echelle spectrometer as an analytical instrument for flame atomic fluorescence spectrometry and for flame atomic emission spectroscopy. The fluorescence was induced by high-pressure xenon arc lamps, which emitted continuum spectra and had higher power ratings, i.e. 1.6 and 2.5 kW, than those normally used for the same purpose. The experimental set-up included two different types of premix burners and one type of total consumption burner. A spherical reflector was applied to improve the utilization of the fluorescence radiation. Two different coatings were tested. None gave the expected enhancement.Detection limits and growth curves were measured for 8 different elements (Ca, Co, Cu, Fe, K, Mg, Na and Ni) in a non-separated air/acetylene flame. The attained detection limits were found to be equally good or somewhat better in flame atomic fluorescence excited with continuum sources than previously reported in the literature, i.e. using similar flames. In flame atomic emission spectroscopy better detection limits have been reported before.     

Atomic fluorescence spectroscopy of beryllium

The atomic fluorescence of beryllium has been observed. A high-intensity beryllium hollow-cathode lamp was used as the source. Oxy-acetylene and nitrous oxide-acetylene flames were studied. A newly designed burner assembly for nitrous oxide-acetylene flames used for atomic fluorescence studies is described. The sensitivity for beryllium at 2349 Å was 10 p.p.m. in the oxy-acetylene flame and 0.5 p.p.m. in the nitrous oxide-acetylene flame. The analytical calibration curves for both flames are presented. No significant interference was found from the cations studied. Some anionic interferences were removed by EDTA. The effects of some organic solvents were investigated.     

开缝石英管原子化技术的改进

近年来,为提高火焰原子吸收光谱法的灵敏度,先后研究过水冷石英管和开缝石英管(简称缝管)原子化技术.前者使灵敏度提高1～2个数量级^[1～3],后者只提高几倍^[4～6].缝管技术比水冷石英管技术的装置简单,操作方便快速,但因其灵敏度不高,应用受到限制.本文以镉为例,探讨了提高缝管技术灵敏度的途径.     

The determination of lead by atomic fluorescence spectroscopy

The atomic fluorescence characteristics of lead are described in air-acetylene, nitrous oxide-hydrogen, and argon-oxygen-hydrogen flames. An electrodeless discharge tube is used as the source of excitation. A detection limit of 0.01 μg/ml of lead in aqueous solution is obtained by measurement of the direct-line fluorescence at 405.8 nm in the argon-oxygen-hydrogen flame. The effect of 100-fold excesses of 30 cations and anions is examined: only aluminium interfered significantly. Effects of multipass optics and signal collection mirrors are examined and their effect on signalnoise ratios is discussed.     

Microdetermination of molybdenum in organometallic compounds by molecular emission and atomic absorption spectrometry

A direct method is described for the determination of molybdenum in mg amounts of organomolybdenum compounds by flame emission or atomic absorption spectrometry. Air/acetylene, air/hydrogen and dinitrogen oxide/acetylene flames were used. The emission of molybdenum oxide is found to be analytically useful in the hydrogen-based flames while the acetylene-based flames are better for atomic absorption. Various organomolybdenum compounds were analysed by both methods as well as by an alternative spectrophotometric method, with satisfactory agreement. The procedure involves simply dissolving the sample in a mixed solvent and aspirating the solution into the flame.     

Evolved-gas zeeman flame atomic absorption spectrometry for the determination of arsenic compounds

An evolved-gas separation/flame Zeeman atomic absorption spectrometric approach is demonstrated for the speciation and determination of arsenic in oyster tissue. No digestion is needed and separation of inorganic arsenic compounds having similar boiling points is achieved. A stoichiometric or air-rich acetylene/air flame for atomic absorption spectrometry is not generally suitable for arsenic determination because of severe ultraviolet absorption interference at 193.7 nm and low sensitivity; polarized flame Zeeman atomic absorption spectrophotometry with a fuel-rich flame is suitable for the detection of traces of arsenic. The evolved-gas separation/Zeeman atomic absorption approach is simple, based on commercially available instrumentation, and useful for the selective determination of major arsenic compounds. Data are given to demonstrate optimal conditions and to show application to oyster tissue.     

Need for fundamental data in atomic fluorescence spectrometry

This paper discusses the needs for fundamental data in atomic fluorescence spectrometry and addresses the diagnostic and theoretical aspects, on the one hand, and the analytical aspects, on the other. Transition probabilities, collision cross sections for excitation and deexcitation, lifetimes, quantum efficiencies, and ionization and recombination cross sections are shown to be the essential fundamental data needed for diagnostic and theoretical studies. It is argued that, analytically, detailed knowledge is indispensable about the excitation and emission spectra as observed with a tunable dye laser as excitation source and a versatile atomizer, such as an ICP, as fluorescence cell.     

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.     

Studies in atomic fluorescence spectrometry: Part II. Interference effects in the determination of tin with various premixed flames

The interference effects are reported for 27 elements, 6 acids and 4 organic liquids on the atomic fluorescence determination of tin with argon-hydrogen, argon-oxygen-hydrogen and argon-separated air-acetylene flames. The addition of1000 p.p.m. iron (III) eliminates most interferences from the elements but not from the acids. The basic trends in the interference effects in the argon-hydrogen flame for the atomic absorption and atomic fluorescence determinations of tin are similar. The detection limit, for an 18.2-s time constant, in the argon-oxygen-hydrogen and argon-hydrogen flames is 0.006 p.p.m. and in the air-acetylene flame it is 0.05 p.p.m. These detection limits are significantly better than previously reported limits. Analytical curves in all three flames studied are linear between the detection limits and 250 p.p.m.     

Emission spectra of nitrous oxide supported acetylene flames at atmospheric pressure

The emission spectra of a premixed flame of acetylene supported by nitrous oxide have been recorded under different fuel-gas mixture conditions. The emission spectra in these flames of a series of metals, for which it is difficult to obtain a significant population of ground state atoms for atomic absorption spectroscopy in more conventional flames, have also been studied. The red secondary zone which is present in the fuel-rich flames shows emission attributable to long-lived CN and NH species which form a strongly reducing atmosphere to inhibit refractory oxide formation from elements such as molybdenum, titanium and aluminium introduced into the flame. An attempt has also been made to explain some of the reactions which may occur between the flame species above the primary reaction zone.     

原子荧光光谱技术在我国发展及标准化应用现状

简单介绍了原子荧光光谱技术的建立及其在国内的发展历程,重点介绍了蒸气发生-原子荧光光谱(VG-AFS)仪在我国的技术研究、仪器研制及应用;详细总结了蒸气发生-原子荧光光谱(VG-AFS)法在我国标准化方面的研究.我国在多通道原子荧光光谱仪、原子荧光形态分析仪等关键技术及其应用等方面取得了开创性的研究成果,并形成了一系列...     

Evaluation of the analytical capabilities of frequency modulated sources in multielement non-dispersive flame atomic fluorescence spectrometry

Frequency modulated sources of Cd and Zn are used to produce modulated atomic fluorescence signals (at two different frequencies) in a non-dispersive flame atomic fluorescence spectrometer. To reduce the flame background level, a chlorine filter, a separated air—acetylene flame, and a solar blind photomultiplier are used. Even so, there is shown experimentally and theoretically to be a multiplex disadvantage, as compared to the conventional single slit scanning dispersive spectrometer, as a result of the flame background photon noise and an additional multiplex disadvantage at high concentrations of an interference, e.g. in the measurement of Zn (213.9 nm), Cd (228.8nm) results in a reduced S/N for Zn when the Cd signal level becomes comparable with the flame background signal level. Little future for multiplexed techniques in atomic flame spectrometry in the u.v.- Visible is predicted.     

Non-linear optical behavior in atomic fluorescence flame spectrometry

The non-linear dependence of the atomic fluorescence radiance upon the irradiance of the excitation source is discussed. Theoretical equations based on the assumption of steady state conditions are derived for a two-level atomic system and for a continuum source of excitation both on a relative as well as on an absolute basis. The theoretical results show that the approach of saturation sets a limit to the fluorescence radiance. The experimental results obtained with the use of a pulsed, tunable dye laser by nebulizing different elements in analytical flames are shown to be in satisfactory agreement with these theoretical results. The theory also predicts that, for a two-level system, the proportional dependence of the fluorescence signal upon the quantum efficiency observed at low irradiances is removed under saturation conditions.     

Sensitive determination of gaseous mercury in air by cold vapour atomic fluorescence spectrometry after amalgamation

A method was developed for the determination of mercury in air, using preconcentration by amalgamation on gold absorbers followed by measurement by atomic fluorescence spectrometry (AFS). The system has a detection limit of ca. 2.0 pg and the precision is in the range 5–10% (relative standard deviation). The accuracy was confirmed by comparison with cold vapour atomic absorption spectrometry. The method was applied to the determination of gaseous mercury in both indoor and outdoor air. As a result of the sensitivity small sample volumes can be analysed and only short sampling times are required. The method is thus suitable for continuous monitoring of mercury and for the fast and reliable determination of gaseous mercury in the atmosphere, even at background levels.     

原子荧光法检验环境空气中汞的含量

目的采用原子荧光法检验环境空气中汞的含量。方法建立微波消解-原子荧光法,研究微波消解前处理效果,并进行精密度、准确度以及样品实验。结果样品空气中汞的含量为1.44、1.09、1.82 ng/m~3。结论原子荧光法检验环境空气中汞的含量前处理简单,样品消解完全,回收率高。     

An investigation of some experimental parameters in atomic fluorescence spectrophotometry

Atomic fluorescence in flames is measured by an adaptation of a commercially available flame spectrophotometer. A study is reported of the effect of background radiation and source scattering on 3 flames, air-propane, air-hydrogen and air-acetylene, and of the effects of variation of fuel gas pressure, zone of measurement in the flame, analysing monochromator slit-width and wavelength of measurement. The air-propane flame appears to offer several advantages. The atomic fluorescence of 10 metals is described; those of Co, Fe and Mn have not been previously reported. Excitation of spectra is achieved by means of an a.c. xenon arc lamp or individual discharge lamps.     

Studies in atomic-fluorescence spectroscopy-VI The fluorescence characteristics and analytical determination of bismuth with an iodine electrodeless discharge tube as source

The atomic-fluorescence characteristics of bismuth atoms in cool nitrogen-hydrogen and argon-hydrogen diffusion flames burning in air are described. Excitation is obtained from the non-resonance iodine line at 2061.63 Å emitted by a microwave-excited electrodeless discharge tube operating at 2450 Mc/s. Fluorescence of the bismuth resonance line at 2061.70 Å is observed and also direct-line fluorescence at 2697 and 3025 A. In addition thirteen other much weaker lines were observed and two unidentified lines at 2880 and 2680 Å. The emissions at 2628 and 2938 Å appear to arise from “thermally assisted direct line fluorescence”. The most intense line at 3025 Å permits linear-dependence analytical atomic-fluorescence measurements to be made in the range 0.1–200 ppm with a detection limit of 0.05 ppm and with no problems of source scatter. No interference was observed from hundred-fold concentrations of fourteen ions. Matrix effects from aluminium and magnesium were overcome by raising the temperature of the cool diffusion flames. A bismuth microwave-excited electrodeless discharge tube was used as a source for atomic-absorption measurement in air-hydrogen and air-propane flames at 2231Å with a detection limit of 1 ppm and a linear-dependence analytical range of 10–100 ppm. With the iodine microwave-excited electrodeless discharge tube the detection limit for atomic absorption was 10 ppm at 2062 Å.