Atomic spectroscopy burner

Burners Sources of heat for laboratory operations or for flame atomic spectroscopy. 

What is the difference between the shape of the burner supporting a flame in atomic emission, atomic absorption, and atomic fluorescence spectroscopy What is the theoretical basis for these differences ... 

Emission spectroscopy utilizes the characteristic line emission from atoms as their electrons drop from the excited to the ground state. The earliest version of emission spectroscopy as applied to chemistry was the flame test, where samples of elements placed in a Bunsen burner will change the flame to different colors (sodium turns the flame yellow calcium turns it red, copper turns it green). The modem version of emission spectroscopy for the chemistry laboratory is ICP-AES. In this technique rocks are dissolved in acid or vaporized with a laser, and the sample liquid or gas is mixed with argon gas and turned into a plasma (ionized gas) by a radio frequency generator. The excited atoms in the plasma emit characteristic energies that are measured either sequentially with a monochromator and photomultiplier tube, or simultaneously with a polychrometer. The technique can analyze 60 elements in minutes. 

Zinc in atomic absorption spectroscopy is remarkably free from interferences as contrasted to the difiiculties encountered in polarography or with colorimetric methods (M4). Gidley and Jones (G4, G5) studied the influence of 27 elements and the only effect seen was a depression with silicon. The absorption enhancement encountered by these authors with haloid acids could be traced back to the attack of the brass burner by the samples and to the use of a brass hollow cathode tube as zinc line source. Methods for the determination of zinc in various metals and alloys are described by these authors. 

R7. Robinson, J. W., and Harris, R. J., Mechanical feed burner with total consumption for flame photometry and atomic absorption spectroscopy. Anal. Chim. Arto 26, 439-445 (1962). 

The burners used in flame spectroscopy are most often premixed, laminar flow burners. Figure 28-11 is a diagram of a typical commercial laminar-flow burner for atomic absorption spectroscopy that employs a concentric tube nebulizer. The aerosol flows into a spray chamber, where it encounters a series of baffles that remove all but the finest droplets. As a result, most of the sample collects in the bottom of the spray chamber, where it is drained to a waste container. Typical solution flow rates are 2 to 5 mL/min. The sample spray is also mixed with fuel and oxidant gas in the spray chamber. The aerosol, oxidant, and fuel are then burned in a slotted burner, which provides a flame that is usually 5 or 10 cm in length. 

Figure 28-11 A laminar-flow burner used in flame atomic absorption spectroscopy. (Courtesy of Perkin-Elmer Corporation, Norwalk, CT.)...

Figure 11.11 Schematic diagram of the slot-burner used in flame atomic absorption spectroscopy.

The next component part in the scheme of the atomic absorption spectrometer is the atomizer. Burners are often used as atomizers in atom absorption spectroscopy. Mixtures of air/acetylene, laughing gas/acetylene or hydrogen/argon are usually used as the fuel gas. The aim of the burner in atomic absorption spectroscopy is to evaporate the solution of the sample and to disintegrate the sample to the atomic state. Especially important for successful analysis is that the path of light through the flame of the burner be made as long as possible. Hence, the use of fissure burners. 

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. 

Figure 10.9. Premix nebulizer-burner system. Adapted from G. D. Christian andF. J. Feldman, Atomic Absorption Spectroscopy Applications in Agriculture, Biology, and Medicine, New York Wiley-Inter-science, 1970, p 80, by permission of John Wiley and Sons.

Compare the advantages and disadvantages of the total-consumption burner and the premix burner in atomic-absorption spectroscopy. 

Amos and Willis suggested another combination of fuel and oxidant, acetylene and nitrous oxide, as another approach to the analysis of refractory elements. The combination of acetylene and nitrous oxide produces a high-temperature flame (2950°C) with little free oxygen to react with the metal elements. This flame is now very successfully used in atomic absorption spectroscopy and permits satisfactory atomic absorption analysis for many refractory elements. Use of nitrous oxide and acetylene requires a burner head that will withstand the temperatures produced by the flame. A common burner head for this combination of fuel and oxidant is 5 cm long and 0.05 cm wide. 

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. 

The behavior of silver, which is not easily oxidized, is quite different as shown in Figure 9-4, a continuous increase in the number of atoms, and thus the absorbance, is observed from the base to the periphery of the flame. By contrast, chromium, which forms very stable oxides, shows a continuous decrease in absorbance beginning close to the burner tip this observation suggests that oxide formation predominates from the start. The.se observations suggest that a different portion of the flame should be used for the determination of each of these elements. The more sophisticated instruments for flame spectroscopy are eqnipped with monochromators that. sample the radiation from a relatively small region of the flame, and so a critical step in the optimization of signal output is the adjustment of the position of the flame with respect to the entrance slit. 

Flame atomizers are used for atomic absorption, fluorescence, and cmi.ssion spectroscopy. Figure 9-.s is a diagram of a typical commercial laminar-flow burner... 

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