Flame emission total consumption

Flame Sources Atomization and excitation in flame atomic emission is accomplished using the same nebulization and spray chamber assembly used in atomic absorption (see Figure 10.38). The burner head consists of single or multiple slots or a Meker-style burner. Older atomic emission instruments often used a total consumption burner in which the sample is drawn through a capillary tube and injected directly into the flame. 

The total consumption type of burner consists of three concentric tubes as shown in Fig. 21.5. The sample solution is carried by a fine capillary tube A directly into the flame. The fuel gas and the oxidant gas are carried along separate tubes so that they only mix at the tip of the burner. Since all the liquid sample which is aspirated by the capillary tube reaches the flame, it would appear that this type of burner should be more efficient that the pre-mix type of burner. However, the total consumption burner gives a flame of relatively short path length, and hence such burners are predominantly used for flame emission studies. This type of burner has the advantages that (1) it is simple to manufacture, (2) it allows a totally representative sample to reach the flame, and (3) it is free from explosion hazards arising from unbumt gas mixtures. Its disadvantages are that (1) the aspiration rate varies with different solvents, and (2) there is a tendency for incrustations to form at the tip of the burner which can lead to variations in the signal recorded. 

Two basic types of burners have been used for atomic absorption. The one is the total consumption or diflFusion burner, of the type long used by Beckman and others for flame emission work. The other is the premix type, in a variety of designs, in which sample, fuel, and oxidant are mixed in a chamber before entering the flame. 

For atomic absorption, many workers recognized the deficiencies of the total consumption burner from the beginning. The Australians almost immediately went over to a premix burner. At the present time, only a rapidly diminishing number of workers are continuing to use the total consumption burner for atomic absorption. (Recently, persuasive evidence has come to light indicating that the premix burner is also superior for flame emission.)... 

Flame emission has traditionally been performed with total consumption burners. However, it has recently been shown that the premix burner, with a nitrous oxide head, is an excellent source for flame emission measurements, and is in many cases superior. In Figure 26, a flame emission scan is shown for aluminum in ethanol, with a premix nitrous oxide burner as a source. 

Several elements (Zn, Pb, Cuy Ni, Ca, Mg, Fe, and Mn) are determined routinely in water samples using atomic absorption spectroscopy. Sodium and potassium are determined by flame emission. The preparation of the samples the analytical methody the detection limits and the analytical precisions are presented. The analytical precision is calculated on the basis of a sizable amount of statistical data and exemplifies the effect on the analytical determination of such factors as the hollow cathode sourcey the ffamey and the detection system. The changes in precision and limit of detection with recent developments in sources and burners are discussed. A precision of 3 to 5% standard deviation is attainable with the Hetco total consumption and the Perkin-Elmer laminar flow burners. 

Turbulent-flow total-consumption burners were the standard for flame emission spectroscopy for a number of years. In spite of certain deficiencies, they also can serve as sample cells for atomic fluorescence. The most common types of total-consumption burners include a built-in sample aspirator system. Figures 9-4 and 9-5 show their general constructional features. Winefordner and Staab (see footnote 2) used this type of burner for their early studies on analytical atomic fluorescence. 

Samples generally are introduced into flames in the form of solutions, by spraying or nebulizing either directly into the flame along with the fuel or indirectly into a chamber to allow coarser droplets to settle out, with the finer aerosol and fuel passing on to the burner. The direct total consumption approach was widely used in emission until the advent of atomic absorption, for which it was less suitable. It was turbulent, audibly noisy, and gave less complete vaporization of solutes. This type of sample introduction is still used in some clinical flame photometers. 

A few of these instruments were imported and used in the USA. But flame photometry was uncommon there until the introduction of the Beckman total-consumption nebuHzer-burner, producing a turbulent oxyacetylene flame. It was used with a high-quality silica prism spectrometer, a photomultiplier detector, and very simple electronic nullbalancing circuitry. Flame emission analysis for many elements was thus widely practised until atomic absorption equipment became available. 

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