Spectroscopy in separated flames-V The argon- or nitrogen-sheathed nitrous oxide-acetylene flame in flame emission spectroscopy

The separation of the premixed nitrous oxide-acetylene flame by sheathing with argon or nitrogen is described. The interconal zone of the hot, slightly fuel-rich flame exhibits low background and noise levels and an extended reducing atmosphere, providing better conditions for the excitation of atoms of elements which form refractory oxides. The limits of detection found for nine such elements are greatly superior to those obtainable in the conventional unsheathed flame under similar conditions.     

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.     

Fate of vanadium determined by nitrous oxide-acetylene flame atomic absorption spectrometry in unburned and burned Venezuelan crude oil

The use of nitrous oxide-acetylene flame atomic absorption spectrometry for the determination of vanadium in burned and unburned Venezuelan crude oil was demonstrated. Results from laboratory controlled experiments suggest that if the temperature typically obtained in the burning of oil as a form of re-mediation (∼1000 °C), then vanadium will not be removed from burning crude oil. This was found to be the case in an open container, on the surface of water, and on the surface of a fixed size sandy soil.     

The determination of rubidium and caesium in geological materials by atomic emission spectrophotometry with a nitrous oxide-acetylene flame

An atomic emission spectrophotometric procedure is presented for the determination of rubidium and caesium at the per cent and p.p.m. levels. A nitrous oxide-acetylene flame and a potassium ionization buffer are used. There is no need for prior separation, pre-concentration or general matrix matching of standards.     

spectroscopy in separated flames-VI The argon or nitrogen-sheathed nitrous oxide-acetylene flame in atomic-absorption spectroscopy

The separation of the premixed nitrous oxide-acetylene flame at a 50-mm slot burner by sheathing with argon or nitrogen is described. In comparison with the conventional flame, the interconal zone of the hot, slightly fuel-rich separated flames provides better conditions for the maintenance of free atoms of elements which form refractory oxides. Optimum conditions for the determination by atomic-absorption spectroscopy of the elements Al, Be, Ge, Mo, Si, Ti, V and Zr in both separated and conventional flames at the same burner have been established. Significant improvement in detection limits and sensitivities is obtained in the separated flames.     

Improvements in repetitive scanning techniques for reducing spectral interferences in flame emission spectrometry

This paper describes several improvements in the use of the repetitive optical scanning (wavelength modulation) technique applied to the correction for spectral interferences due to line, band, and continuum radiation in flame emission spectrometry (FES). A simple and easily constructed mechanical device for performing the repetitive scan is described, and the procedures for optimizing experimental conditions are discussed. A new technique for the correction for spectral line interferences is introduced. Repetitive scanning FES is used for the analysis of several trace elements in NBS SRM-1633 (fly ash), and the precision and accuracy of results are compared to analysis by normal flame emission techniques.     

Atomic-emission spectrometry with an induction-coupled high-frequency plasma source Comparison with the inert-gas shielded premixed nitrous oxide-acetylene flame for multi-element analysis

The performance for trace analysis in solution by atomic-emission spectrometry from a 36-MHz induction-coupled radiofrequency plasma atom-cell is predicted from a simple model and compared with the corresponding characteristics of an inert-gas shielded nitrous oxide-acetylene flame. A longer linear calibration range is predicted for the plasma source owing to the greater freedom from self-absorption under optimum operating conditions, and the long residence time of analyte species confers freedom from solute vaporization interferences. The predictions are verified experimentally and the advantages of the use of the plasma source are demonstrated in the analysis of aluminium alloys for copper, iron, magnesium, manganese, titanium and zinc.     

An experimental and theoretical evaluation of the nitrous oxide-acetylene flame as an atomization cell for flame spectroscopy

The formation of free atoms from aerosols of metal-containing solutions introduced into nitrous oxide-acetylene flames is examined by: (a) inference from well identified reactions and equilibria prevailing in cooler flames; (b) calculations employing a thermodynamic flame model; and (c) experimental observation of relative free-atom number densities in the flames as a function of stoichiometry. The calculated partial pressures of the major natural flame species and some of the spectroscopically observed minor species are presented as a function of the flow ratio of nitrous oxide to acetylene (p). Predicted relative number densities of Na, Mg, Cu, Fe, Li, Be, Al, W, Ti and Si as a function of p are compared with measured free-atom absorbances in an argon-shielded flame. These comparisons were completed for various heights above the burner tip. The data reported show that: (a) the degree of metal atomization in the nitrous oxide-acetylene flame can be adequately described by the equilibrium state; (b) in general, when solute vaporization is complete, there exists a value of ρ at which atomization is complete for metals that form monoxides with dissociation energies less than ~ 6.5 eV; and (c) certain metals may form carbon-containing compounds in the interconal zone.     

Some observations on the interdependence of cyanide concentration and atomization efficiency in the nitrous oxide-acetylene flame

A relationship is derived between CN concentration and atomization efficiency in the C₂H₂-N₂O flame. The relationship is examined under various experimental conditions and β values are estimated for a number of elements. The possibility of complex vapour phase oxide formation by U is considered.     

Improvements in thermospray flame furnace atomic absorption spectrometry

In thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) a nickel atomization tube is placed in the acetylene/air flame on a holder built onto a standard AAS burner head. The liquid to be analyzed is transported by a low or high-pressure pump through a very hot, simple, inexpensive ceramic capillary tip acting as a flame-heated thermospray into the flame furnace. This results in complete sample introduction and increases the residence time of the sample in the absorption volume. This leads for 17 elements to a 3-110-fold improvement in the power of detection compared to conventional flame AAS. The absolute detection limits (3s values, N=25) lie between 0.2 μg l⁻¹ (Zn) and 310 μg l⁻¹ (Se) according to the element. The R.S.D. (N=15) is 1.4-5.5% according to the element and applied concentration. TS-FF-AAS can easily be incorporated on any standard flame AAS instrument and can be automated with a standard autosampler.     

Digital image-based flame emission spectrometry

A digital image-based flame emission spectrometric (DIB-FES) method for the quantitative chemical analysis is proposed here for the first time. The DIB-FES method employs a webcam to capture the digital images which are associated to a radiation emitted by the analyte into an air-butane flame. Since the detection by webcam is based on the RGB (red-green-blue) colour system, a novel mathematical model was developed in order to build DIB-FES analytical curves and estimate figures of merit for the proposed method. In this approach, each image is retrieved in the three R, G and B individual components and their values were used to define a position vector in RGB three-dimensional space. The norm of this vector is then adopted as the RGB-based value (analytical response) and it has revealed to be linearly related to the analyte concentration. The feasibility of the DIB-FES method is illustrated in three applications involving the determination of lithium, sodium and calcium in anti-depressive drug, physiological serum and water, respectively. In comparison with the traditional flame emission spectrometry (trad-FES), no statistic difference has been observed between the results by applying the paired t-test at the 95% confidence level. However, the DIB-FES method has offered the largest sensitivities and precision, as well as the smallest limits of detection and quantification for the three analytes. These advantageous characteristics are attributed to the trivariate nature of the detection by webcam.     

The determination of tin in tin ores and concentrates by atomic absorption spectrophotometry in the nitrous oxide-acetylene flame

Tin in tin ores and concentrates can be determined by atomic absorption measurement in the nitrous oxide-acetylene flame. Solutions are prepared by heating the samples with ammonium iodide and dissolving the resulting tin iodide in dilute hydrochloric acid. Calibrating solutions contain ammonium iodide and hydrochloric acid at approximately the concentrations present in the sample solutions. The method has a limit of detection of 0.02% tin in the sample and is suitable for application to geochemical prospecting samples. The results are similar to those obtained by standard chemical methods.     

A study of some matrix effects in the determination of beryllium by atomic-absorption spectroscopy in the nitrous oxide-acetylene flame

A study has been made of a number of interferences observed in the trace determination of beryllium by atomic-absorption in the nitrous oxide-acetylene flame. The major negative interference caused by the presence of excess of aluminium salts may be overcome by the use of 8-hydroxyquinoline. Magnesium and silicon also depress the Be signal, but most other metals cause enhancement. In most instances the enhancements may be made uniform by the addition of potassium ions to the sample solution.     

Detection of sulphate by flame emission spectrometry

A reasonably simple method for the determination of sulphate is presented. The method is based on disulphur molecular emission, produced in a hydrogen-nitrogen diffusion flame, utilizing a conventional atomic absorption spectrometer, with simple accessories to handle in-line ion-exchange pretreatment. A simplex program was written and used to obtain optimum experimental conditions. Disulphur emission was found to occur at temperatures from below 150°C; the optimum temperature is ca. 200°C. The method can be used for the determination of sulphate down to ca. 10 mg S l^?1.     

Determination of rubidium in blood by flame emission spectrometry

Rubidium in plasma and whole blood was determined by flame atomic emission spectrometry after dilution 10× and 100× respectively with a 2.5 g Cs l^?1 solution used as an ionization suppressor. The method is more sensitive than inductively coupled plasma, and much simpler than, e.g., neutron activation analysis.     

The use of multicomponent analysis in flame emission spectrometry

Summary Two-component analysis has been proposed for the determination of Na and K in HCl by flame emission spectrometry. The method is based on empirical mathematical models approximating the relationship between emission intensity and concentrations of sample components. The results obtained in the analysis of tens of samples of known composition show that the proposed method of determination is more reliable than others usually used.

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Anwendung der Multikomponenten-Analyse in der Flammenemissions-SpektrometrieBestimmung von Na und K in Salzsäure

Zusammenfassung Zur Bestimmung von Na und K in Salzsäure durch Flammenphotometrie wird eine Methode der Zweikomponentenanalyse vorgeschlagen, die auf empirischen mathematischen Modellen beruht, die der Beziehung zwischen Emissionsintensität und Elementkozentration angenähert sind. Ergebnisse von zahlreichen Analysen bekannter Proben beweisen, daß die beschriebene Methode zuverlässiger ist als bisher benutzte andere Verfahren.

     

The use of sample additives in flame emission spectrometry

New kinds of sample additives were investigated to increase the efficiencies of desolvation and atomization in flame spectrometry. Hydrazine and nigrosin were chosen as chemical and dye additives, respectively; an enhancement in the flame-emission signal was obtained in both cases. With nigrosin, it was possible to eliminate completely the interference of phosphate on a calcium emission signal. The increase in the signal for both additives was believed initially to be due to the more rapid evaporation of droplets in the sample aerosol. Further evidence, however, suggested that enhanced vaporization is responsible for the observed signal increase. It is suggested that similar sample additives might be useful also in inductively-coupled plasma emission spectrometry.