Determination of chlorinated hydrocarbons introduced into air/acetylene flames by Fourier transform infrared emission spectroscopy

A Fourier transform spectrometer is used to record the infrared emission from chlorinated hydrocarbons combusted in an air/acetylene flame. In this manner, the chlorinated hydrocarbons are determined by monitoring the infrared emission of hydrogen chloride at 2653 cm(-1). Discussion is presented of the air/acetylene flame background, and the potential spectral interference from the emission of deuterated species. Practical detection limits for chloroform, carbon tetrachloride and methylene chloride in acetone, methanol, and ethanol are solvent independent and are found to be 1.1, 0.80, and 1.0%, respectively. Calibration curves for these three analytes are linear from their detection limits to approximately 55% (v/v). In addition, evidence is presented that flame flicker-noise does not lead to a multiplex disadvantage when the Fourier transform instrument is used for data acquisition.     

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.     

Detection of Polyatomic Species in Non-Premixed Flames Using Tunable Diode Laser Absorption Spectroscopy

Quantitative determinations of polyatomic species in laboratory-scale hydrocarbon diffusion flames using tunable diode laser absorption spectroscopy is discussed. The diode laser used in these studies pumped the ν₄ fundamental of methane and the ν₄ + ν₅ combination band of acetylene in the 1260-1290 cm⁻¹ range in two different burner systems which supported both methane/air and ethylene/air non-premixed flames. For both molecules, the sensitivity of the measurement was a strong function of the local flame temperature, falling off rapidly as temperatures approached 2000 K. The detection limits for acetylene were lower than those for methane because of lower spectral line density in the former experiments.     

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.     

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.     

The role of various flame constituents in the production of atoms in the air—acetylene flame

Atom-formation processes in the premixed air—acetylene flame used in atomic absorption spectrometry are examined. Flame profiles of copper, indium and calcium atoms for five flames of differing acetylene: air ratios are compared with the flame profiles of temperature and the natural flame species C₂, CH and H. The flame profiles of the metals bear little resemblance to the temperature profile. C₂ and CH radicals are shown to be confined to the lower region of the flame (approximately to the region of the reaction zone), whereas H radicals persist far beyond the reaction zone. The strong resemblance of the profile of indium atoms to that of H radicals suggests the participation of H radicals in indium atom formation. Experiments on the action of the flame on solid calcium oxide similarly suggest the involvement of H radicals in the reduction of calcium oxide.     

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.     

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.     

Flame Photometric Determination of Submicrogram Quantities of Boron

A procedure for the determination of submicrogram amounts of boron in aqueous solutions is described. The method is based on measuring the chemiluminescence of the molecular species BO_x in either an air/hydrogen or air/acetylene flame. Detection limits obtained with these flames were 0.004 and 0.06 ppm, respectively. Potential interferences may be removed by ion-exchange chromatography. The procedure is applicable to the determination of boron in potable waters.     

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.     

Construction and performance of a time-multiplex multiple-slit flame atomic fluorescence spectrometer for multi-element analysis

The design and performance characteristics of a new multi-element flame atomic fluorescence spectrometer are presented. Radiation from four hollow-cathode tubes is directed onto an unsheathed air—hydrogen flame. The resulting atomic fluorescence is viewed by a special monochromator with a separate exit slit for each element. The light exiting from all slits is directed to a single photomultiplier tube. The fluorescence signals from different elements are distinguished by a time multiplex approach. Single-element detection limits for ten elements and multi-element detection limits for four elements are presented. The degradation of detection limits by flame background emission noise and effect of flame composition on performance are discussed. Better than 1% precision is obtained for moderate analyte concentrations.     

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.     

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.     

The reaction of n- and i-C4H5 radicals with acetylene

In this article, we discuss the reactions of i-C4H5 and n-C4H5 with acetylene. Both have been proposed as possible cyclization steps, forming benzene or fulvene, in rich flames burning aliphatic fuels. The relevant parts of the potential energy surface were determined from rQCISD(T) calculations extrapolated to the infinite-basis-set limit. Using this information in a Rice-Ramsperger-Kassel-Marcus-based master equation, we have calculated thermal rate coefficients and product distributions for both reactions as a function of temperature and pressure. The results are cast in forms that can be used in modeling, and the implications of the results for flame chemistry are discussed.     

Wavelength-modulated,continuum-source excited atomic fluorescence spectrometric system for wear metals in jet engine lubricating oils using electrothermal atomization

A system for measuring atomic fluorescence of atoms produced via an electrically-heated graphite filament in a flame (acetylene/air or acetylene/nitrous oxide) and excited with a 300-W Eimac xenon are lamp is described. The experimental system also included wavelength modulation for background emission/fluorescence/scatter correction and an optically-triggered electronic integrator for efficient monitoring of the analyte fluorescence signal. Copper, aluminum and molybdenum were determined in jet engine lubricating oil samples (1 μl) with no pretreatment. The determinations are evaluated with respect to the accuracy and repeatability criteria of the U.S. Joint Oil Analysis Program.     

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.     

添加氢气对LPG/空气预混火焰结构的影响

针对氢气添加的LPG(液化石油气)+空气预混火焰结构进行了数值研究, 详细计算了在含氢比a为0%到45%、稀释引子D为21%到16%条件下的自由蔓延火焰, 得到了不同燃烧条件(φ=0.7-1.4)下的绝热燃烧速率变化规律. 由于LPG中的主要成分为丙烷和丁烷, 作者针对C3和C4物质提出了详细化学反应动力学系统, 并针对氢气添加的丁烷燃烧过程进行了数值计算, 得到了与实验相一致的结果, 验证了改进的详细化学机理的有效性. 此外, 进一步计算了对撞双火焰的加氢LPG火焰, 更加深入地探讨了火焰拉伸对燃烧稳定性和温度的影响, 重点研究了φ在0.5到0.7的稀薄燃烧, 验证了氢气添加可以有效提高稀薄燃烧条件下熄火拉伸率, 扩大稀薄燃烧的极限, 增加火焰的稳定性.     

The determination of metals in petroleum samples by atomic absorption spectrometry : Part II. Determination of nickel

Some atomic absorption characteristics of xylene solutions of eight organometallic compounds of nickel in air—acetylene and nitrous oxide—acetylene flames are described. Different absorbances from various nickel organometallic compounds were observed; these differences were not eliminated by using the nitrous oxide—acetylene flame. Serious errors may arise when different organometallic compounds are used for calibration in the determination of nickel in xylene solutions of various petroleum samples. These errors are much less pronounced when nickel is determined by a standard addition technique. The effects of different sample matrices are discussed.     

Effects of Hydrogen Enhancement in LPG/Air Premixed Flame

A numerical study of hydrogen-enhanced liquefied petroleum gas (LPG) + air flames was presented. The variations of the adiabatic burning velocity in different conditions of combustion (?=0.7-1.4) were studied extensively. The hydrogen content in the fuel was varied from 0% to 45% and the dilution factor was from 21% to 16%. Since the major components of LPG are butane and propane, an appropriate chemical kinetic model must be chosen to solve the chemical reaction of C3 and C4 species. Validation of the chemical kinetic model against the fundamental combustion data was performed to insure accuracy. In addition, independent simulations were conducted in the opposed-jet, symmetric, twin-flame configuration. The effects of fluid mechanics, as manifested by the induced strain rate, were also considered. The effects of extinction strain rate on flame temperature and the flammability limits were calculated and the results showed that hydrogen-enhanced LPG/air premixed flames were more stable at high flame strain. The lean flammability limits were extended by the H₂ addition.     

Measuring acetylene concentrations using a frequency chirped continuous wave diode laser operating in the near infrared

Two frequency chirped continuous wave diode lasers operating in the near infrared (IR) at wavelengths of lambda approximately 1.535 microm and lambda approximately 1.520 microm have been used to measure acetylene concentrations using the P(17) and R(9) rotational lines of the (nu1 + nu3) vibrational combination band. The diode lasers were frequency chirped by applying an electrical current pulse to the laser driver at a repetition rate of greater than 1 kHz. As the laser is operated at high repetition rates, more than 1000 spectra per second can, in principle, be acquired and summed, allowing fast accumulation of data, rapid averaging and consequent improvement of the signal to noise ratio and detection limit. Experiments were performed using a single-pass cell with a path length of 16.4 cm, and also an astigmatic multi-pass absorption cell aligned to give a path length of 56 m. Detection limits corresponding to minimum detectable absorption coefficients, alpha(min), of 5.6 x 10(-5) and 7.8 x 10(-8) cm(-1), respectively, were obtained over a 4 s detection bandwidth. These detection limits would correspond to mixing ratios of 21 parts per million by volume (ppmv) and 59 parts per billion by volume (ppbv) of acetylene at 1 atm in air, with the deleterious effects of pressure broadening accounted for. The single-pass cell was used to perform breakthrough volume (BTV) experiments for the low volume adsorbent traps used to pre-concentrate organic compounds in air, taking advantage of the capability of the system to measure concentrations in real time.