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.     

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.     

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.     

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.     

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.     

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.     

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.     

Studies in atomic-fluorescence spectroscopy-VII Fluorescence and analytical characteristics of arsenic, with a microwave excited electrodeless discharge tube as source

The construction of an electrodeless arsenic discharge tube and its use for atomic-fluorescence studies is described. Cool nitrogen-hydrogen and argon-hydrogen diffusion flames as well as normal premixed flames are considered as atom reservoirs and the atomic-fluorescence emission at 15 different wavelengths is evaluated. The diffusion flames give the largest emission signals at arsenic concentrations below 200 ppm, but show a premature curvature at higher concentrations because of the presence of an abnormally high density of arsenic atoms. Above 200 ppm of arsenic, the premixed air-acetylene flame is superior. The limit of detection at 1890 A is 0.2 ppm of arsenic in the nitrogen-hydrogen diffusion flame and 1.0 ppm in the airacetylene flame. A long path-length diffusion flame is also particularly useful in atomic-absorption measurements because it absorbs very little radiation in the far ultraviolet region and gives an abundance of arsenic atoms.     

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.     

Effect of some organic solvents and acids on the laser-induced atomic fluorescence of tin in air-hydrogen flames

The effects of some organic solvents and acids on the atomic fluorescence of tin in air-hydrogen flames have been examined. Ketones and alcohols greatly reduced the florescence sensitivity in fuel rich air-hydrogen flame whereas organic acids generally enhanced the fluorescence signal. The depressive effect of organic solvents was found to be highly dependent on the fuel to oxidant ratio in the flame. An attempt has been made to explain these effects, on the basis of possible reactions occurring in the flame.On leave from Institute of Chemistry, University of the Punjab, Lahore 54590, PakistanOn leave from Department of Analytical Chemistry, University of Zaragoza, Zaragoza, Spain     

Determination of volatile hydride-forming metals in steel by atomic absorption spectrometry

A scheme of analysis is presented for the determination of arsenic, antimony, bismuth, lead, selenium, tellurium and tin in steel by evolution of their volatile hydrides and subsequent atomic absorption spectrometry in an argon—hydrogen-entrained air flame. The method is rapid and applicable to a wide range of steels. Detection limits in steel of 1 p.p.m. for arsenic, antimony, bismuth, selenium and tellurium, 2 p.p.m. for tin and 7 p.p.m. for lead are reported. There is some interference in the determination of lead from copper and nickel, but the method could become a viable alternative to existing procedures in the determination of lead in steels of low alloy content, and in irons. Accuracy and precision data are presented.     

The determination of gallium by atomic absorption spectrometry

The use of a nitrous oxide-acetylene flame for the determination of gallium by atomic absorption spectrometry was compared with the use of air-acetylene flames. The nitrous oxide method provided higher sensitivity and was much less sensitive to acid and base composition and to diverse added salts. Significant matrix and background effects, which occurred when gallium was determined in ore solutions with the air-acetylene flame, were eliminated with the nitrous oxideacetylene flame.     

Study on the elimination of interferences in the determination of strontium by atomic absorption spectrophotometry

Summary Recommended operating conditions for the determination of strontium by atomic absorption spectrophotometry are given for both the air-acetylene and nitrous oxide-acetylene flames. Details are given of interference effects which can occur in the air-acetylene flame and also of a method to eliminate these effects using lanthanum as a releasing agent. In the nitrous oxide-acetylene flame no interference effects occurred if all solutions measured contained an ionisation buffer.

---

Untersuchung zur Ausschaltung von Störungen bei der Bestimmung von Strontium durch Atomabsorptionsspektralphotometrie

Zusammenfassung Arbeitsbedingungen werden für die Luft-Acetylen- und die N₂O-Acetylen-Flamme gegeben. Die Störungen, die in der Luft-Acetylen-Flamme auftreten, werden im einzelnen besprochen und ihre Ausschaltung durch Lanthanzusatz beschrieben. In der N₂O-Acetylen-Flamme treten keine Störungen auf, wenn die Lösungen einen Ionisierungspuffer enthalten.

     

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.     

The atomic absorption spectroscopy of selenium

Selenium can be determined in aqueous solution by atomic absorption spectroscopy at 1960, 2040,2063 or 2075 Å; the sensitivities for these lines with a Techtron 10-cm air-acetylene burner are in the ratio of 1:9:60:93. When a Beckman tripleburner (air-hydrogen) and a triple-pass optical system are used, the most sensitive1960 Å line provides a sensitivity of 0.5 p.p.m. and a detection limit of 1.0 p.p.m. The performence in air-hydrogen and air-acetylene flames is described,and optimum experimental conditions determined.With the Se 1960 Å line and a Techtron 10-cm air-acetylene burner, selenium extracted into methyl isobutyl ketone as its diethyldithiocarbamate complex gives a sensitivity of 0.30 p.p.m.,which is a 2.4-fold increase over that found in aqueous solution.     

Polarization rejection of scattered incident laser light in resonance fluorescence flame atomic detection

In the detection of trace atomic species by resonance fluorescence, scattering of the incident light may cause a significant interference. Fluorescence detection of flame atomized sodium in the presence of intense scattering resulting from the combustion of aluminium in an air-acetylene flame was investigated. A linearly polarized cw dye laser was used as the excitation source. Due to the high polarization of the scattered light, insertion of a polarizer in the detection optics allowed effective rejection of this interference. Improvements in the signal-to-noise and background ratios of 460 and 200, respectively were observed upon introduction of the polarizer. Further improvement was observed employing harmonic saturated spectroscopy.     

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.     

Atomic-fluorescence characteristics and analytical determination of manganese in an air-acetylene flame

The atomic-fluorescence characteristics of manganese atoms in a premixed nitrogen-shielded air-acetylene flame are described. Excitation is obtained at 280 nm from a microwave-excited electrodeless discharge tube. A detection limit of 0-001 ppm for the determination of manganese by atomic-fluorescence spectroscopy is obtained by measurement of the resonance fluorescence observed at this wavelength. In addition to several other weaker atomic-fluorescence signals observed from manganese atoms in the flame, weak resonance fluorescence at 258 and 260 nm from manganese ions stimulated by ion line-emission from the source has been recorded. Linear calibration graphs for atomic-fluorescence measurement at 280 nm are obtained over the range 0.0025-10 ppm of manganese in aqueous solution. Of 26 foreign anions and cations examined for interference at the 1000-fold weight excess level only four produced interference. Large amounts of Si, Th and V interfere by scattering of the incident radiation, while Mg causes depression of the atomic fluorescence by a chemical effect.     

The determination of tellurium by nondispersive atomic fluorescence spectrometry using the hydride generation technique

Atomic fluorescence spectrometry with a nondispersive measuring system is combined with a hydride generation technique for the determination of tellurium. Atomic fluorescence measurement is based on the reduction of tellurium by either metallic zinc or sodium borohydride, introduction of the generated tellurium hydride into a premixed argon (entrained air)-hydrogen flame, and excitation with a tellurium electrodeless discharge lamp. The comparison of the zinc and the sodium borohydride reduction methods is discussed in terms of detection limit, precision and interference. The best attainable detection limits for tellurium are 2ng (0.1 $\text{ng}\text{ml}$) and 30 ng (1.5 $\text{ng}\text{ml}$) with the zinc and the sodium borohydride methods respectively. Analytical working curves obtained from peak-height and peak-area measurements are linear over a range of approximately 4 orders of magnitude. Of the mineral acids examined in the range up to 2.0 m. nitric acid gives a depressing interference in the range greater than 0.5 m in the zinc method, whereas all of the acids greater than 1.0 m give a slight enhancement of the signal in the sodium borohydride method. The presence of several elements including other hydride-forming elements in 1000-fold ratio to tellurium causes a depressing interference, while enhancing interferences from tungsten and vanadium are observed in the zinc and the sodium borohydride methods, respectively. The present system coupled with the zinc method has been applied to the determination of tellurium in several samples of high-purity copper metal after separation of the analyte from copper by passing an ammoniacal solution of the sample through Chelex-100 resin. The results are in good agreement with those obtained by graphite furnace atomic absorption spectrometry.     

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.