Nitrous Oxide Acetylene Research Articles

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.

Eine methode zur bestimmung von fluorkonzentrationen mit hilfe der atomaren absorption

An analytical method for the specific determination of fluorine by atomic absorption spectrometry (AAS) has been developed. The sample is mixed with excess SiO 2 and H 2SO 4 and heated to promote the formation of SiF 4. The gas is fed to an atomization cell, where the atomic concentration of Si is measured by AAS using the resonance line at 251,6 nm, the Si concentration being a measure for the fluorine concentration in the original sample. The authors inuestigated both an acetylene-nitrous oxide flame and a graphite furnace as atomization cells. Relative standard deviations of 6–7% (furnace) and 8.8% (flame) and detection limits of 0.17 μg F (furnace) and 30 μg F (flame) were found. Recoveries in known samples were established to be between 89 and 94 %.

The influence of hollow-cathode lamp line profiles upon analytical curves in atomic absorption spectroscopy

Analytical curves of Ca, Al, Mn, Ga and In in the acetylene-nitrous oxide flame are calculated using line profiles measured with a pressure-scanned interferometer. The effects of hyperflne structure, flame Une shift and finite hollow-cathode lamp line width are determined and found to decrease sensitivity by 10 to 20% and to bend the curves towards the concentration axis according to a quadratic function that causes deviations from a straight line between 2 and 7% at absorbance one. An increase of the lamp current from 5 to 25 mA d.c. enhances the effects mentioned above. It is shown that cooling the hollow cathode raises the sensitivity by only a few per cent and in some cases even reduces sensitivity. The use of a tunable laser as a primary source can improve sensitivity, especially when the atomic line profile consists of several widely spaced hyperfine components.

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.

Interferometric measurements of atomic line profiles emitted by hollow-cathode lamps and by an acetylene-nitrous oxide flame

Source line profiles for eighteen atomic transitions of nine elements emitted by low-current hollow-cathode lamps and by an acetylene-nitrous oxide flame have been measured with a Fabry-Perot interferometer. Distortions caused by instrument broadening are shown to be negligible. Contribution of self-absorption to the profile widths is estimated. In nearly all cases hyperfine structure has a decisive influence upon the observed profile. For thirteen transitions of known hyperfine structure the experimental curves are compared with computer simulated spectra using Gaussian functions to derive the Doppler temperature of hollowcathode lines and Voigt functions to calculate the collision broadening of flame lines. The results show that the Doppler temperatures of hollow-cathode lines range from 400 to 700°K, that flame lines are significantly shifted to the red and that collision broadening in the flame is fully comparable to Doppler broadening, i.e. the a-parameter varies between 0.5 and 1.5.

Ionization interference in the acetylene-nitrous oxide flame

The influence of excess cesium upon the atomic line intensities or absorbances in the acetylene-nitrous oxide flame has been investigated for twenty elements with ionization energies up to 8 eV. Volatilization interference has been corrected for. It is shown that true degrees of ionization can be derived from the intensity increase observed upon cesium addition if corrections for incomplete atomization are made and no molecular ions are formed.

Theoretical calculations of equilibrium concentrations for species generated in analytically important flames

The compositions of several flames at various temperatures and differing oxidant/fuel ratios have been determined theoretically by use of an iterative computer technique based on a thermodynamic model. Systems chosen were: acetylene-nitrous oxide, acetylene-oxygen, acetylene-air, hydrogen-nitrous oxide, hydrogen-oxygen, and hydrogen-air. In view of the importance that acetylene-nitrous oxide flames have in contemporary analytical techniques, this particular system has been examined further when containing a metallic vapor. The calculations indicate that the free-atom fractions for aluminum, molybdenum, silicon, titanium, and tungsten vary with the fuel/oxidant ratio, but that copper and ironfree atom fractions remain relatively invariant with changes in flame stoichiometry.

Some analytical properties of low pressure flames

An investigation has been made into the analytical behaviour of low pressure nitrous oxide-acetylene and oxy-acetylene names, between pressures of ca. 15–300 and 10–100 torr, respectively, for the purposes of atomic emission spectroscopy. Samples were introduced into the flame on a loop of tungsten wire, and the resulting emission pulses measured in the space immediately beyond the edge of the primary reaction zone. Attention was largely concentrated on metals which are difficult to determine in conventional atmospheric flames. Absolute detection limits for Sr, Al, Cr, Cu, Ti and V lie in the range 10 −9–10 −10 g. The relative atomisation efficiences of the flames used were also measured, and were found to increase with decreasing pressure; an effect attributed to the highly reducing properties of a low pressure flame, and one which was felt to account for the high analytical sensitivity obtained in these studies.

Comparison of Theoretical and Experimental Limits of Detection in Atomic Absorption Spectrometry Using Air-Acetylene and Nitrous Oxide-Acetylene Flames

Limits of detection have been calculated for the air-acetylene and nitrous oxide-acetylene flames used in atomic absorption spectrometry using the theoretical treatment developed by Winefordner. Values for the parameters were chosen for these calculations to give the lowest possible limits of detection. These calculated values have been compared with experimentally determined limits of detection. Values of the atom fraction, β, are also estimated by means of this comparison. The values for the air-acetylene flame are in fair agreement; however, the comparison of the nitrous oxide flame showed anomalous behavior. An attempt to explain this is made, as well as a general discussion of the results.

Chemical and spectral interferences in the determination of cobalt in iron and steel by atomic absorption spectroscopy

In the determination of cobalt in iron and steel in air-acetylene flames at least two types of interference may occur In reducing flames the free atom population of cobalt is affected by the presence of alloying elements which behave differently in different acid media. In oxidising flames the formation of a molecular compound of iron, probably FeO, in the flame gives rise to a substantial background absorption. These interferences may be overcome by substituting a nitrous oxide acetylene flame.

The Use of a Triple Pass Optical Arrangement for the Determination of Arsenic and Selenium by Atomic Absorption Spectroscopy in an Inert Gas Shielded Nitrous Oxide-Acetylene Flame

Abstract The utility of the inert gas shielded nitrous oxide-acetylene flame for the determination of arsenic and selenium by atomic absorption spectrometry has been demonstrated elsewhere1. The low background absorbance of the fuel-rich, 50 mm path-length flame (ca 4 and 5% at the As 193.7 and Se 196.0 nm lines respectively) permits the attainment of detection limits which are equal to, or somewhat superior to, those obtainable with the air-acetylene flame. The AAS sensitivity (that concentration producing 1% absorption), however, is decreased; this is the result of the shorter path length of this flame compared to that employed for air-acetylene (100 mm) and the lower concentration of analyte produced in the larger volume of gas used to support the flame.

Burner Design Criteria and Variables Affecting Flashback of Acetylene Flames

A study is presented on the operating characteristics of burners employing premixed, laminar flow air–acetylene and nitrous oxide–acetylene flames. The variables affecting flashback of these flames have been investigated and found to be critically dependent on such factors as burner port diameter, gas flow, fuel–oxidant ratio, and burner construction. Because the theory previously developed for stable flame formation on isothermal burners is not directly applicable to most burners used in flame spectrometry, an operational theory of flashback is developed. In accordance with this working model, safe limits of operation for conventional burners are examined and presented and important burner design criteria are established, including experimental quenching diameters for both circular port and slot-type burners.

A Comparison Study of Detection Limits Using Flame-Emission Spectroscopy with the Nitrous Oxide—Acetylene Flame and Atomic-Absorption Spectroscopy

The minimum detection limits using flame-emission spectroscopy with the nitrous oxide–acetylene flame and using atomic-absorption spectroscopy were determined under optimum instrumental and flame-operating conditions for 68 elements, using the same nebulizer system, the same instrument, and signal integration techniques. Based on these studies, 27 elements show equal detectability by the two methods, 15 are more sensitive by flame emission, and 26 are more sensitive by atomic absorption. Results are compared and discussed with respect to theoretical prediction.

Direct Nebulization of Metal Samples for Flame Atomic-Emission and Absorption Spectroscopy

A device for transforming solid-metal samples into an aerosol of fine metal particles has been combined with a flame spectroscopic method for the determination of trace impurities and alloying elements in steels. The aerosol generator is a simple apparatus in which the sample serves as the cathode of a low-current dc-arc discharge. Constant movement of the cathode spot results in uniform sampling of a relatively large area. A flowing gas stream transports the aerosol particles from the arc discharge to the nitrous oxide–acetylene flame. Analytical curves for the determination of chromium, manganese, and nickel in steel are shown. The method provides a very rapid means of determining trace elements and alloy constituents in metals without the complications attendant to dissolution procedures.

The Determination of Iron in Used Lubricating Oil

Iron analyses performed on used gas turbine lubricating oil samples by several variations of rotating disk–spark emission spectrography, atomic absorptiometry, and x-ray fluorescence spectrometry are compared with a quantitative wet chemical technique. The results indicate that emission spectrography with a cobalt internal standard, atomic absorptiometry with a nitrous oxide–acetylene flame, and x-ray fluorescence, both dispersive and nondispersive, are the most reliable instrumental methods. The iron contained in the samples exists primarily as particulates 1 µ or less in diameter.

The Characterization of Rhenium by Atomic-Absorption Spectroscopy in Nitrous Oxide-Acetylene Flames: The Analysis of Organorhenium Compounds

This investigation of the atomic-absorption characteristics of rhenium included studies of optimum operating conditions, detection limits, interferences from various inorganic acids, and the effect of organic-solvent ratios on absorption. Atomic-absorption analysis of some organorhenium complexes are also described.

Non-dispersive systems in atomic fluorescence spectroscopy—II: Comparison of nitrous oxide-supported and air-supported flames

A nitrogen-sheathed, water-cooled burner for use with nitrous oxide-acetylene and nitrous oxide-hydrogen flames is described, and results of atomic fluorescence measurements in four different flames are given for beryllium, magnesium, aluminium, germanium, titanium, palladium and platinum. The nitrogen-sheathed nitrous oxide-acetylene flame, in conjunction with a high-intensity hollow-cathode lamp and a non-dispersive system, should be useful for the determination of metals forming refractory oxides and having their resonance lines below 300 nm. The nitrous oxide-hydrogen flame is found to be of no more value than it has proved to be in flame emission or atomic absorption work. The use of filters in conjunction with an RCA 931A photomultiplier is also described.

Calculation of the Effect of Silicon on the Atomisation of Lithium and Magnesium in Air- and Nitrous Oxide-Acetylene Flames

Abstract The calculations performed in this study were similar to those discussed previously1 utilising a computer technique based upon the minimisation of free energy. The programme is capable of handling forty species at each of ten temperatures and a variety of flame stoichiometries can be studied in one operation. In general the concentrations are calculated in moles per mole of feed and those of gaseous species in volume per cent. The effects of nebulising water have been fully investigated on the nitrous oxide- and air-acetylene flames and are hence neglected in this study.

A Flame Emission Interference in the Atomic Absorption Determination of Calcium

Calcium is reported to be the element most frequently determined by atomic absorption, and the nitrous oxide–acetylene flame is recommended for this determination. We wish to point out a condition in which the strong calcium atomic emission from this high temperature flame markedly reduces the sensitivity of the atomic absorption determination and causes bending of the absorption analytical curve.

Radiolysis of acetylene-nitrous oxide mixtures and the effect of carbon dioxide

Acetylene-nitrous oxide mixtures were irradiated to low dose levels (≈4·1 × 10 19 eV g −1) with 60Co γ-radiation. Nitrogen was formed, increasing with nitrous oxide concentration to a limiting value G(N 2) ∞ = 18·2 ± 1·7 [equivalent to 4·7 × G(electron)], for mixtures containing around 20% N 2O. There was a small yield of carbon monoxide [ G(CO) = 0·32 ± 0·08], and the polyacetylene was oxygenated. Addition of sulphur hexafluoride prevented formation of nitrogen and when carbon dioxide was added to the acetylene-nitrous oxide system, nitrogen yields were reduced, tending to a lower limit around G(electron). The results can be explained on the basis of electron capture by nitrous oxide, followed by a short-chain process initiated by reaction of O − ion with acetylene. Estimated relative rate constants for the proposed mechanism are given. Benzene was also formed, and the initial yield [ G(C 6H 6) = 11·1 ± 1·2] was not affected by electron scavenging, indicating that ion-neutralization reactions are not involved in the cyclization process.