Atomic-fluorescence spectroscopy of magnesium with a high-intensity hollow-cathode lamp as line source

Atomic fluorescence of magnesium is possible in air-propane or air-acetylene flames at 285.21 nm, using a high-intensity hollow-cathode magnesium lamp for excitation. The technique permits determinations of magnesium in the range 0.01–5 p.p.m., i.e. with more than 10 times the sensitivity of the atomic absorption method even for this most sensitive element. The detection limit in either flame is 1 ng/ml (signal: noise ratio 1 : 0.75). In a nitrous oxide-acetylene flame, atomic fluorescence may be carried out with linear signal/concentration dependence up to 100 p.p.m. without interference even from metals such as aluminium, titanium, etc. at a 1000-fold excess ratio to magnesium. A brief comparison is made with atomic absorption using the same source and equipment.     

OH在火焰中浓度分布图像及与温度关系的PLIF和CARS研究

用平面激光诱光（ＰＬＩＦ）技术了平面火焰炉、狭缝缝火焰的单脉冲激光诱导ＯＨ荧炙。由平面荧光图可得到氢氧基相对浓度分布和它的宽度。对扩散火焰,高温区在ＯＨ带内侧;ＯＨ带的外侧则是火焰的边界,相干反斯托克斯拉斯拉曼光谱（ＣＡＲＳ）的测量结果对比提出了有力的佐证。湍流火焰的ＰＬＩＦ图则清晰地显示出火焰面的不规则性,氢氧基的ＰＬＩＦ图像是研究火焰结构和流场的有力工具。     

Experimental estimation of fluorescence power efficiencies of several atoms in three turbulent flames used in atomic fluorescence flame spectrometry

An experimental system for the measurement of approximate atomic fluorescence power efficiencies of atoms in turbulent flames used in atomic fluorescence flame spectrometry is described. An expression is derived for the power efficiency as a function of instrumental parameters. Experimentally measured power efficiencies for eleven elements in fuel-rich oxyhydrogen, fuel-rich oxyacetylene, and fuel-rich hydrogen/argon/entrained air flames are given. The power efficiencies vary considerably from one spectral line to another, but as a result of the entrainment of ambient air into the turbulent flames, the values obtained in different flames are approximately equal. It is also shown that fluorescence radiation should rarely produce a significant error in atomic absorption spectrometry.     

Studies in atomic-fluorescence spectroscopy-V The fluorescence characteristics and determination of antimony

Atomic-fluorescence of antimony may be generated in an air-propane flame by nebulizing aqueous solutions of antimony salts whilst irradiating the flame by means of a microwave-excited electrode-less discharge tube operating at 30 W. The strongest fluorescence is exhibited by the (4)S(11 2 ) --> (4)P(1 3 ) 2311 A resonance line and weaker signals are observed at the 2068 and 2176 A resonance lines and at four intercombination lines, at 2598, 2671, 2770 and 2878 A. A process of thermally assisted direct-line fluorescence is postulated to account for the otherwise inexplicable intensity of the 2598 A line emission. Atomic-fluorescence spectroscopy at 2176 A permits the determination of antimony in the range 0.1-120 ppm with a detection limit of 0.05 ppm. With the same equipment and source, the range of measurement for atomic-absorption was 6-120 ppm and the detection limit was 1 ppm. No interferences were observed from 100-fold molar amounts of Cd, Co, Cu, Fe, Hg, K, Mg, Mn, Mo, Na, NH(4), Pb and Zn or from arsenate, chloride, nitrate, phosphate and sulphate.     

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.     

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.     

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.     

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.     

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.     

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.     

Pyrene measurements in sooting low pressure methane flames by jet-cooled laser-induced fluorescence

This paper presents in detail the study we carried out concerning the pyrene measurement by jet-cooled laser-induced fluorescence (JCLIF) in different sooting low pressure methane flames. The aim of this paper is both to demonstrate the potentialities of this technique for the measurement of such moderately sized polycyclic aromatic hydrocarbons under sooting flame conditions and to provide new experimental data for the understanding and the development of chemical models of the soot formation processes. Several concentration profiles of pyrene measured in different sooting flame (various pressure and equivalence ratio) are presented. The validation of the JCLIF method for pyrene measurements is explained in detail as well as the calibration procedure, based on the standard addition method, which has been implemented for the quantification of the concentration profiles. Sensitivity lower than 1 ppb was obtained for the measurement of this species under sooting flame conditions.     

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.     

A study of some interferences in the atomic absorption spectrophotometry of magnesium

The effects of some cations, anions and complexing agents on the absorbance of magnesium in the air-propane flame are investigated in detail. The results have enabled the mechanisms of magnesium atom production in this flame to be deduced, and have clarified the nature of the interferences.     

Spectroscopy in separated flames--VII: Determination of bismuth by atomic-fluorescence spectroscopy in a separated air-acetylene flame with electronically modulated electrodeless discharge tube sources

The application of electronically modulated and unmodulated bismuth and iodine electrodeless discharge lamps as sources for the excitation of bismuth atomic fluorescence in conventional and nitrogen-separated air-acetylene flames has been investigated. Separation of the flame results in improved detection limits for bismuth even when a modulated source is employed. The effect of 500-fold weight excesses of foreign ions on the determination of bismuth at 302.46 nm with a modulated iodine source and separated flame has been studied; only calcium and zirconium are found to cause significant interference. The determination of bismuth in aluminium alloy samples is reported.     

H and O atom detection for combustion applications: study of quenching and laser photolysis effects

A method is in development which should allow the determination of absolute number densities of H and O atoms in flames from two-photon laser-excited fluorescence measurements. The calibration will be based on reference experiments in a discharge-flow reactor. In this study, the influence of fluorescence quenching and the generation of additional H and O atoms by laser photolysis of the flame gases is investigated. Consequences for typical hydrogen-oxygen flame conditions are discussed.     

An evaluation of the spectral noise distribution in analytical flames

The spectral distribution of noises (total, shot and flicker) in a variety of flames has been measured using a computer-controlled spectrometer system. Emission spectra and fluorescence spectra (excited by an Eimac xenon arc lamp) are presented for air/acetylene, nitrous oxide/acetylene, nitrous oxide/propane, air/hydrogen, and an iso-octane liquid fuel flame. Conclusions concerning the predominant type of noise and its cause in each flame are discussed as well as the implications for the analytical flame spectroscopist.     

Electrochemical diffusion potential in the gas phase

Potentiometric based electrochemical measurement of diffusion potential at a junction between two flowing flame plasma gases is described. A flame electrochemical cell was constructed using a specially designed burner, which supports two individual flames, each fed by separate premixed methane/oxygen/nitrogen streams. The two flames were in intimate contact, creating a flowing fluid gaseous junction. By aspirating metal salt solutions into these premixed feed gases, the concentration gradient at the interface between the two flames may be controlled. A measurable electrochemical diffusion potential was formed at this junction, the magnitude of which was dependent on the concentration ratio of charged species with different mobilities. In our flame electrolyte, the dominant charged species were atomic or molecular cations and electrons, which have a difference in mobilities of approximately three orders of magnitude. A two-electrode system, in conjunction with a high impedance electrometer was used to measure the potential difference across the flame electrochemical cell. The measured potential difference was analysed using theory developed for the liquid junction potentials by the Henderson equation.     

Some interferences in the atomic absorption spectrophotometry of calcium

The effects of anions, cations and complexing agents on the absorbance of calcium in the air-propane flame are investigated. Mechanisms for the various enhancing and depressive effects are suggested.     

基于激光诱导荧光法的同轴射流火焰中羟基自由基、甲醛、发热率与一氧化氮的二维可视化测量

对现有单一组分羟基自由基(OH)平面激光诱导荧光系统(PLIF)装置进行功能扩展研发,在不增加激光器和探测器的情况下,拓展了甲醛(CH2 O)、发热率(heat release rate,HRR)和一氧化氮(NO)三个参量的PLIF成像测试模块.同时,利用所研制的同轴射流火焰装置开展了所建立的多参量PLIF测量技术的实...     

An experimental and theoretical evaluation of the nitrous oxide-acetylene flame as an atomization cell for flame spectroscopy

The formation of free atoms from aerosols of metal-containing solutions introduced into nitrous oxide-acetylene flames is examined by: (a) inference from well identified reactions and equilibria prevailing in cooler flames; (b) calculations employing a thermodynamic flame model; and (c) experimental observation of relative free-atom number densities in the flames as a function of stoichiometry. The calculated partial pressures of the major natural flame species and some of the spectroscopically observed minor species are presented as a function of the flow ratio of nitrous oxide to acetylene (p). Predicted relative number densities of Na, Mg, Cu, Fe, Li, Be, Al, W, Ti and Si as a function of p are compared with measured free-atom absorbances in an argon-shielded flame. These comparisons were completed for various heights above the burner tip. The data reported show that: (a) the degree of metal atomization in the nitrous oxide-acetylene flame can be adequately described by the equilibrium state; (b) in general, when solute vaporization is complete, there exists a value of ρ at which atomization is complete for metals that form monoxides with dissociation energies less than ~ 6.5 eV; and (c) certain metals may form carbon-containing compounds in the interconal zone.