Spectroscopy in separated flames-II The use of the separated air-acetylene flame in long path atomic absorption spectroscopy

The application of a separated air-acetylene flame to the determination of several elements by long-path atomic-absorption spectroscopy is described. The factors which govern the stability and reproducibility of the separated flame have been investigated. High sensitivity and stability and low background absorption are obtained in the the determination of zinc, iron, copper, mercury, magnesium and silver by the method described.     

Spectroscopy in separated flames-IV: application of the nitrogen-separated air-acetylene flame in flame-emission and atomic-fluorescence spectroscopy

The primary and secondary combination zones of an air-acetylene flame have been separated by a stream of nitrogen flowing parallel to the flame to prevent access of atmospheric oxygen to its base. The flame is very stable over a wide range of fuel-air mixture strengths, and organic solvents may be aspirated without difficulty. The low flame background enables thermal-emission and atomic-fluorescence measurements to be made with high sensitivity. Bismuth, for example, has been determined in the range 5-200 ppm by its thermal emission at 306.8 nm, with a detection limit of 2 ppm in aqueous solution, and in the range 1-10 ppm with a detection limit of 0.3 ppm in 50% ethanolic solution. Zinc and cadmium have been determined at 213.9 nm and 228.8 nm by atomic-fluorescence spectroscopy in this flame with detection limits of 2 x 10(-4) ppm and 5 x 10(-4) ppm respectively, vapour-discharge lamps being used as sources of excitation. The results obtained represent a considerable improvement over those available by the same methods in a conventional air-acetylene flame.     

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.     

Systematic investigation of aluminium interferences with the alkaline earths in flame atomic absorption spectrometry

Summary Aluminium interferes with the absorption of Mg and Ca in the air-acetylene flame to such an extent that the corresponding absorbances may fall even to zero. This well-known chemical interference can be overcome with the nitrous oxide-acetylene flame, completely in the case of Mg, however only to a restricted extent in the case of Ca. Mg and Ca with concentrations of the AAS-working range in aqueous solutions and Cl^– or NO ₃ ^– as anions (in an aqueous HCl or HNO₃ matrix, respectively), were determined in the air-acetylene flame with continuously rising Al portions and with (or without) 0.25% Cs as radiation buffer, in order to quantify the degree of these interferences. The same was done to evaluate the extent of the suppression of those interference when using a releaser or protector reagent in both the air-acetylene and the nitrous oxide-acetylene flame. After the decrease of absorption in the air-acetylene flame by forming thermally stable Mg or Ca aluminates, a rapid increase (positive interference) occurs unexpectedly in the presence of Cl^–±Cs and with further rising Al contents. This effect still appears for Ca also in the hotter nitrous oxideacetylene flame, however, only in a restricted extent. In the air-acetylene flame the undisturbed absorptions for Mg and Ca (i.e. the starting data without Al) are nearly reached again within the range of the positive interference. This supports the assumption that in consequence of a continuous equilibrium change in the flame because of the rising Al content and in the presence of Cl^– and ±Cs the formation of only pure Al oxides now generates the release of Mg and Ca (instead of the thermally stable aluminates in the beginning). In the air-acetylene flame interferences of 1000 mg/l Al are completely removed by an addition of 1% releaser-La, when measuring up to 0.2 mg/l Mg and up to 4 mg/l Ca. The extent of releasing Mg and Ca is effective only up to that Al concentration range which leads to the absorption maximum of Mg and Ca. In the nitrous oxideacetylene flame 5000 mg/l Al are compensated when determining up to 1 mg/l Mg. In the case of Ca, which is detected up to 4 mg/l, interferences of 1000 mg/l Al are only avoided by using the nitrous oxide acetylene flame together with 1% releaser-La. The excellent sensitivity of Ca in this flame (in contrast to the air-acetylene flame) permits a strong dilution, lowering thereby the interfering Al concentration, too. For Mg the same option is valid because of its high sensitivity in the air-acetylene flame.     

Characterization and elimination of the interfering effects of foreign species in the atomic-absorption determination of iron

The inhibition-release titration method has been used to study interference effects in flame atomic-absorption determination of iron. Interferences from anions, cations and complexing agents with the atomic-absorption of iron when a stoichiometric air-acetylene flame is used, can be obviated by a preliminary treatment of the sample solution with sulphosalicylic acid to convert the iron into the same complex before aspiration, thus giving a constant environment for the iron in the flame processes.     

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 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.     

Atomic-fluorescence spectroscopy of lead

The fluorescence spectrum of lead excited with a high-intensity hollow-cathode lamp has been investigated and the probable mechanism of fluorescence transitions is suggested. It is confirmed experimentally that the most intense fluorescence line at 405.78 nm is mostly due to direct-line fluorescence. The premixed air-hydrogen flame, the separated air-acetylene flame, and the oxy-hydrogen flame diluted with argon have been used, the last mentioned giving a detection limit of 0.02 ppm with the line at 405.78 nm.     

相对峰吸收法测定几种元素在乙炔-空气火焰中的原子化度

本文提出以相对峰吸收法测定元素在乙炔-空气火焰中的原子化度,并讨论了方法的理论基础。采用Cu作参考元素,测定了Na、Mg、Cr和Mo等元素在乙炔-空气火焰中的原子化度。另外,还研究了火焰组成和测量高度对四种元素的吸光度的影响,以及对Na和Mg的原子化度的影响。实验表明,这两个因素对原子化度都有影响,而火焰组成的影响较大。所以,原子化度是一个相对的数值,它与测量条件有密切关系。     

Determination of calcium by atomic-absorption spectrometry in samples dissolved by acid mixtures

Summary The effect of lanthanum addition to the fluoboric-boric acid matrix for the determination of calcium by atomic absorption spectrometry has been studied. The samples were decomposed in a pressure vessel. The addition of hydrochloric acid before lanthanum addition in the dissolved samples allowed the use of the air-acetylene flame, which gives more accurate data than the acetylene-nitrous flame and is easier to handle.     

Application of an oxygen-shielded air-acetylene flame to atomic spectroscopy

A burner has been designed which provides an oxygen-shielded air-acetylene flame for atomic-absorption work. The chemical reducing properties of the oxygen-shielded flame operated under fuel-rich conditions are enhanced by the higher C: O ratio obtainable in the flame and by the higher flame temperature just above the reaction zone. The flame is inherently essentially free from the risk of flashback, and is offered as an alternative to the nitrous oxide-acetylene flame for use with certain types of equipment and for particular applications.     

The oxygen-shielded air-acetylene flame in emission analysis

Flame-emission studies have been made on 18 elements in the inner zone of an oxygen-shielded air-acetylene flame. The shielded flame gave higher emission sensitivity that that of the C(2)H(2)N(2)O flame for Cu and Tl, and comparable sensitivity for a number of other elements, but poorer sensitivity for elements forming stable refractory oxides in flames. The inner zone of the shielded flame has low emission-background and high flame-temperature, permitting good analytical sensitivity to be obtained with relatively low-resolution optical equipment.     

Spectroscopy in separated flames-III Use of the separated nitrous oxide-acetylene flame in thermal emission spectroscopy

The separation of a premixed nitrous oxide-acetylene flame at a modified commercial burner is described. The reducing interconal zone of the fuel-rich separated flame exhibits low radiative background. The reducing atmosphere and high temperature of this flame result in an effective medium for the excitation of the atomic line spectra of the refractory elements. The use of the fuel-rich flame in the flame photometry of these elements has been investigated.     

The determination of magnesium in silicates by atomic absorption spectroscopy

The determination of magnesium in silicates by atomic absorption spectroscopy using a hot flame is discussed. Interference by aluminium observed, in the air-acetylene flame is overcome by using the hotter nitrous oxide-acetylene flame. There is some evidence to suggest that the alkali metals interfere in this determination but this is not confirmed in the results obtained on standard rock samples. Values for magnesium are given for some new rock standards recently distributed by the U.S. Geological Survey.     

Determination of total chromium in sediments by FAAS

The determination of chromium by flame atomic absorption spectroscopy (FAAS), e.g. as performed for environmental matrices, is still a controversial matter as can be concluded from a literature review. Most controversy is due to the measurement conditions or the effect of the interferences; other conditions such as digestion seem to be less critical. Consequently, this paper reports a systematic study of the instrumental settings for the two flame modes that are most widely used: air-acetylene and nitrous oxide-acetylene. In connection with the study of experimental conditions, possible interferences are investigated involving nineteen cations and some anions in different ratios Cr:interferent. Different releasers to overcome interferences are considered. The results are critically compared with current literature. For the operational conditions the quality parameters such as the linear range, detection limits, precision and accuracy are established. Although the nitrous oxide-acetylene flame is mostly recommended, this study reveals that a better choice can be the use of a fuel-rich air-acetylene flame with the addition of 1% 8-hydroxyquinoline (oxine) as protective agent. The method is applied to and validated by four sediment certified reference materials.     

The application of a piezoelectric scanning Fabry-Perot Interferometer to the study of atomic line sources—III: Use of the channeled spectra produced with a continuum source for studies of the absorption line-width for calcium atoms in flames

An instrumental arrangement has been developed for the interferometric study of the half-width of atomic lines in absorption using a spectral continuum source. The variation of observed half-width of the calcium absorption line at 422·67 nm with calcium concentration has been examined in air-acetylene and nitrous oxide-acetylene flames supported as cylindrical flames with and without flame shielding and at long path burners. Extrapolation of the curves obtained to zero added calcium concentration in the flame may allow for correction for self-absorption and flame characteristics and calculation of collisional broadening half-widths and damping constants (a-parameters).     

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.     

Determination of chromium in low-alloy steels by atomic-absorption spectrophotometry

Iron causes severe depression of the signal in determination of chromium by atomic-absorption spectrophotometry in an air-acetylene flame. This effect can be eliminated by addition of hydroxylamine hydrochloride and use of a fuel-rich flame. Addition of iron to the standard solutions is not necessary for up to 300 ppm of iron in the test solution.     

Determination of calcium in cement by flame-emission spectrometry with strontium as internal standard

A combination of strontium as internal standard and lanthanum as releasing agent is recommended for direct flame-emission spectroscopic determination of calcium in cement, an air-acetylene flame being used.     

Interference by acids in the determination of molybdenum by atomic absorption spectrometry

The nature of the acid environment in the determination of molybdenum by atomic absorption spectrometry is shown to be of considerable importance. The most favourable conditions are provided by dilute hydrochloric acid and especially nitric acid. Sulphuric and phosphoric acids are not recommended because of their marked but opposite effects. The air-acetylene flame gives more reproducible results than the nitrous oxide-acetylene flame.