In atomic absorption

This same principle, as indicated earlier, is used in atomic absorption spectroscopy and UV absorption. 

Atomic absorption, along with atomic emission, was first used by Guystav Kirch-hoff and Robert Bunsen in 1859 and 1860, as a means for the qualitative identification of atoms. Although atomic emission continued to develop as an analytical technique, progress in atomic absorption languished for almost a century. Modern atomic absorption spectroscopy was introduced in 1955 as a result of the independent work of A. Walsh and C. T. J. Alkemade. Commercial instruments were in place by the early 1960s, and the importance of atomic absorption as an analytical technique was soon evident. 

In atomic absorption spectroscopy, the correction of the net absorbance from that due to the sample matrix. 

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. 

Use of glow-discharge and the related, but geometrically distinct, hoUow-cathode sources involves plasma-induced sputtering and excitation (93). Such sources are commonly employed as sources of resonance-line emission in atomic absorption spectroscopy. The analyte is vaporized in a flame at 2000—3400 K. Absorption of the plasma source light in the flame indicates the presence and amount of specific elements (86). 

Sodium and Potassium. Sodium and potassium can be deterrnined by either atomic emission or absorption. Large concentrations of sodium can interfere with the potassium deterrnination in either of these methods. Excess sodium can be added to both the potassium standards and samples to minimize any variations in the samples. Proper positioning of the flame helps reduce sodium interference in atomic absorption. 

A NEW WAY TO CORRECT A NON-SELECTIVE LIGHT ABSORBANCE IN ATOMIC ABSORPTION SPECTROMETRY, BASING ON PRELIMINARY REGISTRATION OF MOLECULAR... 

Although APDC complexes are soluble in many organic solvents, it is found that 4-methylpent-2-one (isobutyl methyl ketone) and heptan-2-one (n-pentyl methyl ketone) are, in general, the most satisfactory for direct nebulisation into the air/acetylene flame used in atomic absorption spectroscopy. 

Discussion. Because of the specific nature of atomic absorption spectroscopy (AAS) as a measuring technique, non-selective reagents such as ammonium pyrollidine dithiocarbamate (APDC) may be used for the liquid-liquid extraction of metal ions. Complexes formed with APDC are soluble in a number of ketones such as methyl isobutyl ketone which is a recommended solvent for use in atomic absorption and allows a concentration factor of ten times. The experiment described illustrates the use of APDC as a general extracting reagent for heavy metal ions. 

It should be noted that in atomic absorption spectroscopy, as with molecular absorption, the absorbance A is given by the logarithmic ratio of the intensity of the incident light signal I0 to that of the transmitted light / i.e. 

A schematic diagram showing the disposition of these essential components for the different techniques is given in Fig. 21.3. The components included within the frame drawn in broken lines represent the apparatus required for flame emission spectroscopy. For atomic absorption spectroscopy and for atomic fluorescence spectroscopy there is the additional requirement of a resonance line source, In atomic absorption spectroscopy this source is placed in line with the detector, but in atomic fluorescence spectroscopy it is placed in a position at right angles to the detector as shown in the diagram. The essential components of the apparatus required for flame spectrophotometric techniques will be considered in detail in the following sections. 

Instead of employing the high temperature of a flame to bring about the production of atoms from the sample, it is possible in some cases to make use of either (a) non-flame methods involving the use of electrically heated graphite tubes or rods, or (b) vapour techniques. Procedures (a) and (b) both find applications in atomic absorption spectroscopy and in atomic fluorescence spectroscopy. 

To summarise, it may be stated that almost all interferences encountered in atomic absorption spectroscopy can be reduced, if not completely eliminated, by the following procedures. 

In practice, the emission line is split into three peaks by the magnetic field. The polariser is then used to isolate the central line which measures the absorption Ax, which also includes absorption of radiation by the analyte. The polariser is then rotated and the absorption of the background Aa is measured. The analyte absorption is given by An — Aa. A detailed discussion of the application of the Zeeman effect in atomic absorption is given in Ref. 51. 

The monochromator should be capable of high resolution, typically 0.04 nm. This feature is most desirable if the AAS is adapted for flame emission work good resolution is also desirable for many elements in atomic absorption. 

Nitrogen monoxide is used as an oxidizer in biproplnt systems with carbon monoxide or methanol-w as fuels, and it is added to N2O4 to advantageously modify the frp and bp of this oxidizer. It is also employed as a high enthalpy flow medium in hypersonic wind tunnels (Ref 10), and as an oxidizing gas in atomic absorption spectroscopy (Ref 12). Qf -19.7 kcal/mole (Ref 3)... 

Figure 24, The basic principle used in atomic absorption. The sample is sprayed into the flame, and the calcium and magnesium emission from the lamp is absorbed. The extent of absorption is measured on the detector arm translated in terms of concentration.

Spectral overlap of emission and absorption wavelengths Is a potential cause of Interference In atomic absorption spectrometry (57) Thus, (a) the emission line of Fe at 352.424 nm Is close to the resonance line of N1 at 352.454, (b) the emission line of Sb at 217.023 nm Is close to the resonance line of Pb at 216.999 nm, and (c) the emission line of As at 228.812 nm Is close to the resonance line of Cd at 228.802 (57). To date, these practically coincident spectral lines have not been reported to be of practical Importance as sources of analytical Interference In atomic absorption analyses of biological materials. 

Aggett, J. and Sprott, A. J. "Non-Flame Atomization In Atomic Absorption Spectrometry". Anal. Chlm. Acta (1974),... 

Klrkbrlght, G. F. "The Application of Non-Flame Atom Cells In Atomic Absorption and Atomic Fluorescence Spectroscopy. 

Electrically Heated Furnace In Atomic Absorption In "Trace Substances In Environmental Health - V . (D. D. 

Matousek, J. P. and Stevens, B. J. "Biological Applications of the Carbon Rod Atomizer in Atomic Absorption Spectroscopy". Clin. Chem. (1971), J7, 363-368. 

Norris, J. D. and West, T. S. "Some Applications of Spectral Overlap in Atomic Absorption Spectrometry . Anal. 

Reeves, R. D., Patel, B. M., Molnar, C. J., and Wlnefordner, J. D. "Decay of Atom Populations Following Graphite Rod Atomization In Atomic Absorption Spectrometry". Anal. Chem. 

Mixtures of acetylene and dinitrogen oxide used to create flames in atomic absorption apparatus detonate in the presence of perchloric acid. 

Table 8.20 Main characteristics of solid sampling in atomic absorption spectrometry...

Principles and Characteristics Flame emission instruments are similar to flame absorption instruments, except that the flame is the excitation source. Many modem instruments are adaptable for either emission or absorption measurements. Graphite furnaces are in use as excitation sources for AES, giving rise to a technique called electrothermal atomisation atomic emission spectrometry (ETA AES) or graphite furnace atomic emission spectrometry (GFAES). In flame emission spectrometry, the same kind of interferences are encountered as in atomic absorption methods. As flame emission spectra are simple, interferences between overlapping lines occur only occasionally. 

Fujiwara K, McHard JA, Foulk SJ, Bayer S, Winefordner JD (1980) Evaluation of selectivity in atomic absorption and atomic emission spectrometry. Canadian J Spectrosc 25 18... 

Winefordner JD, Vickers TJ (1964) Calculation of limit of detectability in atomic absorption flame spectrometry. Anal Chem 36 1947... 

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