Atomic absorption burner

Fig. 2 Comparison of atomic absorption burner (A) and ICP argon plasma torch (B). (Courtesy of Perkin-Elmer Instruments.)...

Atomic Absorption Determination. The precipitate is washed through the filter into a 25-ml filter flask with 20 ml of MEK-HNO3. This solution is then aspirated into the atomic absorption burner (we used a... 

An alternative method consists of running the gasoline sample through the gas chromatograph to separate the components, which are then introduced, one by one, directly to the atomic absorption burner. The atomic absorption spectrophotometer, which is set up for lead determination, records a peak absorption for each lead compound as it passes from the chromatograph. The method is standardized by using... 

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. 

Lee [524] described a method for the determination of nanogram or sub-nan ogram amounts of nickel in seawater. Dissolved nickel is reduced by sodium borohydride to its elemental form, which combines with carbon monoxide to form nickel carbonyl. The nickel carbonyl is stripped from solution by a helium-carbon monoxide mixed gas stream, collected in a liquid nitrogen trap, and atomised in a quartz tube burner of an atomic absorption spectrophotometer. The sensitivity of the method is 0.05 ng of nickel. The precision for 3 ng nickel is about 4%. No interference by other elements is encountered in this technique. 

For flame emission measurements, burners of the Meker type with a circular orifice covered by a grille are used whereas in atomic absorption spectrometry, a slit burner is preferred. In both cases, the flame consists of two principal zones or cones (Figure 8.21(b)). The inner cone or primary... 

Atomic fluorescence spectrometry has a number of potential advantages when compared to atomic absorption. The most important is the relative case with which several elements can be determined simultaneously. This arises from the non-directional nature of fluorescence emission, which enables separate hollow-cathode lamps or a continuum source providing suitable primary radiation to be grouped around a circular burner with one or more detectors. 

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 ... 

The heart of a traditional atomic absorption spectrometer is the burner, of which the most usual type is called a laminar flow burner. The stability of the flame is the most important factor in AAS. Typical working temperatures are 2200 2400°C for an air-acetylene flame, up to 2600-2800°C for acetylene-nitrous oxide. The fraction of species of a particular element that exist in the excited state can be calculated at these temperatures using the Boltzmann equation ... 

The design of a conventional atomic absorption spectrometer is relatively simple (Fig. 3.1), consisting of a lamp, a beam chopper, a burner, a grating monochromator, and a photomultiplier detector. The design of each of these is briefly considered. The figure shows both single and double beam operation, as explained below. 

Flame atomic absorption spectrometry can be used to determine trace levels of analyte in a wide range of sample types, with the proviso that the sample is first brought into solution. The methods described in Section 1.6 are all applicable to FAAS. Chemical interferences and ionization suppression cause the greatest problems, and steps must be taken to reduce these (e.g. the analysis of sea-water, refractory geological samples or metals). The analysis of oils and organic solvents is relatively easy since these samples actually provide fuel for the flame however, build-up of carbon in the burner slot must be avoided. Most biological samples can be analysed with ease provided that an appropriate digestion method is used which avoids analyte losses. 

The whole atomizer may be water cooled to improve precision and increase the speed of analysis. The tube is positioned in place of the burner in an atomic absorption spectrometer, so that the light passes through it. Liquid samples (5-100 mm ) are placed in the furnace, via the injection hole in the centre, often using an autosampler but occasionally using a micro-pipette with a disposable, dart-like tip. Solid samples may also be introduced in some designs, this may be achieved using special graphite boats. The sample introduction step is usually the main source of imprecision and may also be a source of contamination. The precision is improved if an autosampler is used. These samplers have been of two types automatic injectors and a type in which the sample was nebulized into the furnace prior to atomization. This latter type was far less common. 

Atomic absorption spectrometer with air-acetylene burner head. Pressurized acetylene cylinder. Air compressor. 

The thermal device used to elevate the temperature consists of a burner fed with a gaseous combustible mixture or, alternatively, in atomic absorption, by a small electric oven that contains a graphite rod resistor heated by the Joule effect. In the former, an aqueous solution of the sample is nebulised into the flame where atomisation takes place. In the latter, the sample is deposited on the graphite rod. In both methods, the atomic gas generated is located in the optical path of the instrument. 

Figure 14.4—The diverse components of a single beam atomic absorption spectrophotometer. Model IL 157, built in the 1980s. 1, source 2, burner 3, monochromator 4, detector (design according to Thermo Jarrell Ash Corp.).

Figure 14.8—Burner for an atomic absorption instrument. This type of burner is used in models 3100 3300 from Perkin-Elmer. (Reproduced by permission of Perkin Elmer.)...

Figure 14.16—Elements determined by AAS or FES. Most elements can be determined by atomic-absorption or flame emission using one of the available atomisation modes (burner, graphite furnace or hydride formation). Sensitivity varies enormously from one element to another. The representation above shows the elements in their periodic classification in order to show the wide use of these methods. Some of the lighter elements, C, N, O, F, etc. in the figure can be determined using a high temperature thermal source a plasma torch, in association with a spcctropholometric device (ICP-AbS) or a mass spectrometer (1CP-MS).

Apparatus. A Perkin-Elmer model 303 atomic absorption spectrometer equipped with a DCR-1 readout accessory and a strip chart recorder was used for all determinations. A Boling burner was used for all determinations made in the air-acetylene flame except for copper where a single-slot, high-solids burner was used. The nitrous oxide burner was used for refractory elements. Burner and instrument settings used were those recommended by the manufacturer s handbook. 

For a selected list of elements (26) there is another acid treatment procedure which is readily applicable to the analysis of orange juice this procedure involves hydrolysis with moderately strong nitric acid to breakdown most of the sugars and to decrease the size of the pulpy constituents. The solution is then filtered, diluted, and measured by atomic absorption. For elements that can be determined with an air-acetylene flame using a high solids (three slot) burner, this procedure offers a useful alternative. Fricke et al. (33) also mentions the utility of this method and gives comparative results on the use of this method in sample preparation. 

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