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.     

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.     

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.     

Determination of calcium, magnesium and strontium in soils by flow injection flame atomic absorption spectrometry

Several procedures for the determination of Ca, Mg and Sr in soils have been compared on the basis of the accuracy of analysis of two NIST reference materials (Montana Soils SRM 2710 and SRM 2711). Samples were dissolved in a mixture of hydrofluoric and nitric acids in sealed vessels in a microwave oven and in teflon beakers on a hot plate. The digests obtained from both dissolution methods were evaporated to dryness in an attempt to remove silicon. Boric acid was added to prevent the precipitation of the lanthanum releasing agent (as lanthanum fluoride) and potassium was added as an ionization buffer. Determinations were made by flame atomic absorption spectrometry with both the nitrous oxide-acetylene flame and the air-acetylene flame, with calibration either by standard additions or against external standards matrix matched with respect to nitric acid, boric acid, lanthanum and potassium. The silicon remaining in the solution was also determined by external calibration. A single-line flow injection manifold was used to overcome any problems due to the presence of high dissolved solids. A volume of 300 mul was injected into a water carrier stream flowing at 8 ml min(-1). To determine Ca in the air-acetylene flame, it was necessary to remove silicon. Magnesium was determined in either flame without complete removal of the silicon, however, for the determination of Sr, it was necessary to remove the silicon and use the nitrous oxide-acetylene flame. The indicative value for Sr in SRM 2710 was too low: the value determined was 360+/-30 mug g(-1).     

Spectrophotometric determination of the pH scale in ethane-1,2-diol

A highly selective method is described for the determination of gallium at the ppm-level in manganese nodules and geological reference samples. After dissolution of the sample, gallium is adsorbed on Dowex 1 (chloride form) from hydrochloric acid solution containing titanium trichloride, which reduces iron(III) so that it is not adsorbed. After elution with dilute nitric acid and evaporation, gallium is determined by atomic-absorption spectrometry with an air-acetylene flame.     

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.     

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.     

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).     

Spectroscopy in separated flames-I. The use of the separated air-acetylene flame in thermal emission spectroscopy

The separation of a premixed air-acetylene flame is described. The interconal zone of this flame exhibits very low radiative background, and is only slightly cooler than that of a normal air-acetylene flame. The use of the separated flame in flame photometry, for which it has several pronounced advantages, has been investigated.     

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.

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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.

     

The application of a piezoelectric scanning Fabry-Perot interferometer to the study of atomic line sources—II: Line-widths for calcium in air-acetylene and nitrous oxide-acetylene flames

The variation in observed half-width of the calcium 422.7 nm line with calcium concentration has been studied interferometrically in air-acetylene and nitrous oxide-acetylene flames supported as cylindrical flames, with and without flame shielding and inert gas separation, and at a long path burner. Extrapolation of the curves obtained to zero added calcium concentration is shown to permit correction for self-absorption and calculation of interaction broadening half-width and damping constants (a-parameters).     

The significance of the CrO(4)2- chemical equilibrium HCr(4)- equilibrium in the determination of chromium(VI) by flame spectrometry

Chromium atomic absorption for Cr(VI) solutions in the air-acetylene and air-hydrogen flames is pH-dependent, but not in the nitrous oxide-acetylene flame. The effect is shown to occur as a result of the HCrO(-)(4) chemical equilibrium CrO(2-)(4) equilibrium, and may cause significant errors in the determination of chromium by atomic-absorption Spectrometry unless the pH of sample and standard solutions is controlled.     

Matrix effects on the determination of manganese in geological materials by atomic-absorption spectrophotometry under different flame conditions

Suppression caused by five of the seven matrix elements studied (Si, Al, Fe, Ca and Mg) was observed in the atomic-absorption determination of manganese in geological materials, when synthetic solutions and the recommended oxidizing air-acetylene flame were used. The magnitude of the suppression effects depends on (1) the kind and concentration of the interfering elements, (2) the type of acid medium, and (3) the concentration of manganese to be determined. All interferences noted are removed or alleviated by using a reducing nitrous oxide-acetylene flame. The atomic-absorption method using this flame can be applied to the determination of total and extractable manganese in a wide range of geological materials without interferences. Analyses of six U.S. Geological Survey rock standards for manganese gave results in agreement with the reported values.     

Interferences and their elimination in the determination of the noble metals by atomic-absorption spectrophotometry

A number of serious interferences in the determination of the noble metals by atomic-absorption spectrophotometry have been investigated, and ways of eliminating them considered. The use of the nitrous oxide and acetylene flame reduced many of the interferences but also reduced the sensitivity. Additions of lanthanum, copper sulphate, copper + cadmium sulphate, uranium, and vanadium as releasing agents were effective in the removal of interferences for one or more of the noble metals in the air-acetylene flame. Uranium additions were found to be effective in removing mutual interferences associated with the noble metals (osmium and indium were not tested) whereas vanadium removed mutual and base-metal interferences. The precision and accuracy of methods of analysis based on the use of uranium and vanadium were acceptable, and the application of these methods to the analysis of noble metals collected by various procedures is briefly discussed.     

Determination of gallium by extraction and atomic absorption measurement

Summary Gallium can satisfactorily be determined by atomic absorption in organic solvents using air-acetylene or nitrous oxide-acetylene flame. It is recommandable to extract it as chloride complex. By employing MIBK and nitrous oxide-acetylene flame a considerable increase of absorption signal and sensitivity and elimination of the interference effect of a large number of metal ions was achieved.

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Bestimmung von Gallium durch Extraktion und Atomabsorptionsmessung

Zusammenfassung Mit Hilfe der Luft/Acetylen- oder N₂O/Acetylen-Flamme kann Ga aus organischen Lösungsmitteln mit guten Ergebnissen bestimmt werden. Zu bevorzugen ist die Extraktion als Chloridkomplex, Extraktion mit MIBK und Verwendung der N₂O-Acetylen-Flamme. So kann eine wesentliche Zunahme des Absorptionssignals, eine Verbesserung der Empfindlichkeit und Ausschaltung des störenden Einflusses zahlreicher Fremdionen bewirkt werden.

     

Atomabsorptionsspektrometrische Bestimmung von Iridium mit Hilfe einer Lachgas-Acetylenflamme

Zusammenfassung Die Lachgas-Acetylenflamme (max. Temperatur 2955° C) wird erfolgreich zur Gehaltsbestimmung von komplex gebundenem Iridium verwendet, da die Absorptionen analytisch günstige Werte ergeben. Zur hinreichenden Anpassung von Eich- und Probenmaterial werden die Proben nach einem beschriebenen Verfahren chloriert und dann gemessen, ohne daß chemische Interferenzen bei der Absorption zu beobachten sind.

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Determination of iridium by atomic-absorption spectrometry using a nitrous oxide-acetylene flame

The nitrous oxide-acetylene flame (max. temp. 2955° C) is used successfully for the determination of iridium in a complex of not yet completely known stoechiometric composition. The absorption reaches values comparable to those produced by the colder (max. temp. 2300° C) air-acetylene flame. To adjust the samples to the Irstandard [IrCl₆]^2– a chlorination of the material is performed before measuring. No chemical interference can be observed after this treatment. The nitrous oxide-acetylene flame eliminates at last the trouble caused by incomplete chlorination of the samples with respect to the standard.

     

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.     

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.     

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。