J.D. Bradshaw

Five laser-excited fluorescence methods for measuring spatial flame temperatures. 1: Theoretical basis.

Five methods for measurement of flame temperatures based upon laser-excited fluorescence are discussed with respect to the derived expressions, the assumptions necessary, the advantages, and the disadvantages. The use of each of the five methods for measuring spatial flame volumes (~<1 mm(3)) and temporal flame temperatures (corresponding to ~<1-microsec time period) is given. The five methods consist of one based upon linearity between the fluorescence signal and the laser spectral irradiance, three based upon saturation, and a fifth, which is not critically dependent upon the laser spectral irradiance.

Atomic and ionic fluorescence spectrometry with pulsed dye laser excitation in the inductively-coupled plasma

Abstract The atomic and ionic fluorescences of iron, tin, barium and indium excited by flash-lamp-and nitrogen laser-pumped pulsed dye lasers in the inductively-coupled plasma (ICP) are studied. Noise sources are investigated and detection limits are compared to the techniques of ICP-emission and laser-excited atomic fluorescence spectrometry.

Application of laser-excited atomic fluorescence spectrometry to the determination of iron

Abstract A frequency-doubled, flashlamp-pumped tunable dye laser is used to excite the Stokes direct-line atomic fluorescence transition of iron (296.7 nm/373.5 nm). Limits of detection are determined with single (0.6 ng/ml) and multipass (0.2 ng/ml) and with a l s time constant (a 0.06 ng/ml limit detection is obtained with an 8 s time constant). Noise sources limiting precision at both low (background flame emission shot and flicker noise) and high concentrations (laser pulse to pulse variability) concentrations are investigated and the technique is used for the determination of iron in simulated fresh water NBS SRM-1643), unalloyed copper (NBS SRM-394) and fly ash (NBS SRM-1633).

Thermally Assisted Fluorescence: A New Technique for Local Flame Temperature Measurement

The theoretical basis of a new technique called thermally assisted atomic fluorescence for measurement of local spatial-temporal flame temperatures is given. In this method, the ratio of fluorescence signals from a radiatively excited level and a higher collisionally excited level or from two higher collisionally excited levels of an inorganic probe, such as In or TI, is related to the flame temperature. The conditions necessary for the measured flame temperature to be identical to the translational (Boltzmann) flame temperature are given. The experimental system and conditions for making flame temperature measurements, which consists basically of a single pulsed dye laser and a gated detector, are described. The assumption of steady-state conditions is discussed as well as several anomalies in terms of fluorescence from certain energy levels of Tl. The accuracy and precision of the measured flame temperatures for several methane-air flames are discussed.

Rate equation solution for the temporal behavior of a three-level system

The time behavior of a three-level system has been solved with general assumptions using the rate equation approach and under a pulsed spectral irradiance with rectangular shape. Three different specific cases, corresponding to possible conditions for inorganic atom seeds in atmospheric flame, have been investigated making use of literature values for the collisional and radiative rate constants. Results of these calculations are presented for Tl and Ga atoms when excited via the transitions 1 ? 3, 2 ? 3, and 1 ? 2 under different source spectral irradiances, flame conditions, and the most significant collisional coupling constants between the various levels.

Analytical and spectral features of gas-phase chemiluminescence spectrometry of arsenic and antimony

Abstract Intense emissions are produced in the u.v. and visible regions when arsine and stibine are introduced into a flow-type furnace—hydrogen diffusion flame system, when the flame is surrounded by oxygen. The emissions in the range 240–300 nm are attributed to AsO and SbO. The emission characteristics seem to be due to chemiluminescence based on the reaction between atomic analyte and oxygen. The detection limits are 0.05 μAs (10 ppb) at 429 nm and 0.1 μ Sb (20 ppb) at 369 nm.

Atomic absorption inhibition release titration as a method of studying releasing and inhibiting effects: Studies of the mechanism of formation of calcium phosphate compounds

Abstract The results of releasing and inhibiting studies by means of a new, semi-automatic technique termed atomic absorption inhibiting release titration (a.a.i.r.t.) are reported. This method is based on the releasing or inhibition effect (enhancement or depression, respectively) of an atomic absorption signal by a given chemical component; namely, the releasing element is titrated by a solution of magnesium chloride and phosphoric acid while the magnesium signal is monitored by atomic absorption flame spectrometry. This method was employed for the continuous observation and explanation of processes occurring during evaporation/vaporization. On the basis of the mole ratios obtained at characteristic points on the titration curves, a possible mechanism of tricalcium phosphate formation is presented. It was established that this compound was formed through a chain of intermediate compounds of the x CaO· y P 2 O 5 type.

An evaluation of the spectral noise distribution in analytical flames

Abstract 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.

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

Abstract 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.

A continuum-source single-detector resonance-monochromator for atomic-absorption spectrometry

The detector, for atomic-absorption spectrometry, consists of a furnace into which a constant concentration of the element to be analysed is atomized. Resonance radiation is excited by the light from a xenon-arc lamp which traverses the burner flame. The resonance radiation passes through a tunable grating filter and is measured with a photomultiplier.