Atomic flames

It has already been shown that different problems can arise at 1 atm. and at low pressures. One of the more interesting observations is that at 1-2 torr in C2H2/02 and C2H4/02 flames large concentrations of C2-are present, and no C2H- is observed (9) yet if the pressure is increased to 10 torr, only C2H - is observed (compare Figures 3 and 4). In addition, in 1-atm. flames (20) and in atomic flames at 1-10 torr and at low temperatures C2H- predominates (29). C2- decays more rapidly than does... 

Flame Inductively coupled plasma Flame Electrothermal atomizer Flame... 

From the above definition it is quite evident that the sensitivity takes no cognizance of the noise-level of the base-line, therefore, it is more or less of no use as a definite guide to the least quantity of an element which may be estimated. However, the sensitivity of a 1% absorption-is a pure theoretical number only that would undergo a change solely depending on the efficiency of the lamp (hollow-cathode-lamp), atomizer, flame-system employed, monochromator (prism, grating used), and finally the photomultiplier used. 

One often unsuspected source of error can arise from interference by the substances originating in the sample which are present in addition to the analyte, and which are collectively termed the matrix. The matrix components could enhance, diminish or have no effect on the measured reading, when present within the normal range of concentrations. Atomic absorption spectrophotometry is particularly susceptible to this type of interference, especially with electrothermal atomization. Flame AAS may also be affected by the flame emission or absorption spectrum, even using ac modulated hollow cathode lamp emission and detection (Faithfull, 1971b, 1975). 

In atomic flames, where one might expect direct excitation of a metal atom as third body, an intermediate is often involved instead. For example, in studies of excitation of iron by nitrogen atoms in CO it has been postulated that Fe is excited by collision with excited N2 or CO produced as third bodies in the atom recombination process178. Brennen and Kistiakowsky55 studied the excitation of nickel, iron and other metals in active nitrogen and concluded that the metal atom is not excited as third body in the recombination process, but by interaction with the metastable N2 (A3XI ). 

This radiative recombination is observed in flames181,213, electric arcs214, shock tubes194,215,216, and atomic flames192,217-219. In flames and arcs, the emission consists of diffuse bands on a continuum, whereas in atomic flames (the reaction of O with CO at low pressures and room temperature) there is no continuum and clear vibrational structure extends from below 3000 A out to at least 6000 A. The process has not been studied as thoroughly as O+NO, but enjoys the same complexities and uncertainties. 

Pressure jet atomizer flames. In this flame, the momentum of the spray is small compared with the momentum of ihe air flow. 

Moore et studied the reactions of O atoms with NH3 and N2H4 in atomic flames. The emission observed from the NH3 + O flame was very weak compared... 

The principal methods recommended for measuring non specific absorption or background in atomic flame absorption spectrometry are as follows ... 

Chemical Reactions. Products from gas-phase chemical reactions can also be trapped in rare gas matrices, and those products which absorb light can be studied by optical spectroscopic techniques. For example (31), the products from a low pressure 1 mm. of Hg) atomic flame of oxygen atoms plus acetylene were allowed to leak through a small oriflce in a borosilicate glass reaction chamber, where they were mixed with an excess of gaseous krypton at 1(H mm. of Hg pressure. The mixture was condensed on a quartz window cooled to liquid helium temperature. The only detectable small free radical found was HCO, but it was present in considerable quantities. Similar experiments by Harvey and Brown (23) showed that HNO could be easily produced and trapped from the gas-phase reaction of hydrogen atoms plus nitric oxide. 

No discussion of emission spectroscopy would be complete without mention of the atomic flame studies of Michael Polanyi. In these now-classical investigations, Polanyi and his co-workers (ref. 39 and the references cited therein) ob-... 

AAS Atomic Absorption Spectroscopy Atomize (flame, electro, thermal, etc.) Light e.g., glow discharge Absorption spectrum - - Concentralion ol atomic species (quantitative, using standards) 1,2... 

The flame is responsible for production of free atoms. Flame temperature and the fuel/oxidant ratio are very important in the production of free atoms from compounds. Many flame fuels and oxidants have been studied over the years, and temperature ranges for some flames are presented in Table 6.1. In modem commercial instmments, only air-acetylene and nitrous oxide-acetylene flames are used. 

Back extraction is desirable when the organic solvent used cannot be introduced directly into the atomizer (flame, graphite furnace, or plasma). In electrothermal atomization, organic solvents are spread within the graphite tube and because of this the sensitivity is often better for aqueous solutions. The reproducibility of the determination is usually worse in organic solvents than in aqueous solutions. 

Keywords Additive Atomizer Flame Nanoparticles Pyrolysis... 

Most instruments constructed for atomic flame emission and atomic absorption spectroscopy have dispersions in the range of 15-35 A/mm. For example, the Perkin-Elmer 290B uses a grating with a dispersion of 16 A/mm, the Jarrell-Ash Dial-atom uses a grating with a dispersion of 33 A/mm, the Hilger-Watts Atomspek uses a prism with a dispersion of 17 A/mm at 2000 A, and Aztec Instruments model AAA-3 uses a grating with a reciprocal linear dispersion of 16 A/mm. 

The sensitivity of the AAS determination is defined by the slope of the calibration curve in its initial straight part. A convenient characteristic of the sensitivity is the characteristic concentration - the analyte concentration that produces 1% absorption (or 0.0044 absorbance) signal. The characteristic concentrations of the elements for flame atomizers are between 0.01 and 10mgl , for electrothermal atomizers - 2-3 orders of magnitude lower. Factors affecting the sensitivity are the oscillator strength (the probability) of the corresponding electron transition, the type of the atomizer - flame or electrothermal - and the efficiency of atomization. 

Furthermore, in atomic flame systems, where [CHO ] > > [H30 ], it is also found that [CH30 ] > > [CH50 ]. 

In atomic fluorescence spectrometry (AFS), the analyte is introduced into an atomizer (flame, plasma, glow discharge, furnace) and excited by monochromatic radiation emitted by a primary source. The latter can be a continuous source (xenon lamp) or a line source (hollow cathode lamp, electrodeless discharge lamp, or tuned laser). Subsequently, the fluorescence radiation, which may be of the same wavelength (resonance fluorescence) or of longer wavelength (nonresonance fluorescence), is measured. 

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