**2. Atomic spectroscopy: general principles**

Every element has a characteristic atomic structure, with a small, positively charged nucleus surrounded by a sufficient number of electrons necessary to maintain neutrality. Electrons settle into orbitals within an atom and one of the electrons can also jump from one energy level to the higher level by acquiring the necessitated energy (**Figure 1**). This energy is provided by colliding with other atoms, such as heating-AES, photons derived from light-AAS and AFS, or high-energy electrons-XRF. Possible transitions happen, when the required energy reaches to the difference between two energy states (ΔE). A neutral atom may exist at a low energy shell

#### **Figure 1.**

*Energy level diagrams to show transitions associated with (a) AAS, (b) AES, and (c) AFS. The vertical arrows indicate absorption or emission of light.*

or ground state (E0), or at any of a group of excited states depending on how many electrons have been jumped to higher energy levels (E′') although it is normal to think for the first transition. Each element has a unique energy level and the ΔEs associated with transitions between those levels.

The ΔE for movements of *valence* electrons in most elements meets the energy equal to UV/visible radiation. The energy of a photon (E) is computed with the following equation:

$$\mathbf{E} = \mathbf{h}\mathbf{u} \tag{1}$$

where h is Planck's constant (6.63 × 10<sup>−</sup>34 Js) and υ the frequency of the waveform corresponding to that photon. The relationship between wavelength and frequency is showed by the equation below:

$$\mathbf{D} = \frac{\lambda}{\mathbf{c}} \tag{2}$$

where c is the speed of light and λ the wavelength. Thus,

$$\mathbf{E} = \frac{\mathbf{h}\mathbf{c}}{\lambda} \tag{3}$$

**3**

**Figure 2.**

*Schematic diagram of an AAS, AES, and AFS instrument.*

*Atomic Spectroscopy*

unique to a given element.

*DOI: http://dx.doi.org/10.5772/intechopen.89269*

of lamps considered to be light sources.

**3. Atomic spectroscopy: instrumentation**

It follows from Eqs. 1–3 that the wavelengths of the absorbed or emitted light are

Formation of the atomic vapor i.e. atomization is the major principle of emission, absorption, and fluorescence techniques. The most critical component of instruments used in atomic spectroscopy is the atomization sources and sample introduction devices with an associated spectrometer for wavelength selection and detection of light. Atomization involves the several key (the basic) steps: solvent removal, separation from anion and other elements of the matrix, and reduction of ions to the ground state atom. The design of an AFS instrument is similar to those for AAS and AES except that the light source and the detector are located at a right angle (**Figure 2**). *A light source* which emits the sharp atomic lines of the element to be determined is selected. There are two types of light sources used in these instruments: continuous sources and line sources. A continuous source, also called to as a broad-band source, emits radiation over a broad range of wavelengths. A line source, on the other hand, emits radiation at specific wavelengths, but this source of radiation is not as pure as radiation from a laser. **Table 1** provides a list of most common kinds

*The atomizer* is any device which will produce ground state atoms as a vapor into the light path. Many atomizers utilized for AFS are similar to those used for AAS and AES. The atomizers most commonly used in these techniques are flames and electrothermal atomizers [10]. The flame provides for easy and fast measurements with few interferences and is preferred at any *appropriate concentration* for the analyte. Flame atomizers contain a pneumatic nebulizer, an expansion chamber, and an air-acetylene laminar flame with a 10 cm path length. The typical pneumatic nebulizer for sample introduction is insufficient, and although elements such as Na and K can be determined in biological samples by flame AES, flame atomization is more suitable for AAS and AFS. AAS measurements can detect concentrations at approximately 1 μg/ml (ppm) or more. Devices are being developed to overcome these limitations of the typical nebulizer. Atomization can be reached to 100% and the devices can also generate the sample as a pulse flow rather than the continuous flow. Most systems use a graphite tube which is heated electrical energy, a technique called graphite furnace atomization, although other materials are sometimes employed. A programmed sequence of the furnace temperature is used in electrically heated graphite tube. With this atomizer, 10–50 μl of test solution is dried, organic material is destroyed, and the analyte ions dissociated from anions for reduction to ground state atoms. This atomizer also produces *temperatures* up to 3000 K which allows to form an atomic vapor of refractory elements such as aluminum and chromium. Since the analyte is atomized and retained within a small volume furnace, this procures a dense atom population. The technique is extremely sensitive as it allows one to detect a few μg/ml concentrations of the analyte. Although the technique is widely used for AAS, electrothermal atomization will

and a specific transition, ΔE, is associated with a unique wavelength.

When light of a specific wavelength enters an analytical system, outer shell electrons of the corresponding atoms will be excited as energy is absorbed. As a result, the amount of light transmitted from the system to detector will be reduced, this is understood as AAS (**Figure 1a**).

Under appropriate circumstances, outer shell electrons of vaporized atoms may be excited by heating. As these electrons return to the more stable ground state, energy is lost. As **Figure 1b** shows, some of this energy is emitted as light, which can be measured with a detector, this is AES.

Some of the radiant energy absorbed by ground state atoms can be emitted as light as the atom returns to the ground state i.e. AFS (**Figure 1c**).

When high-energy photons strike to a massive particle, it can excite an inner shell electron of the atom. The forming inner orbital vacancy can be filled with an outer shell electron. The transition is created by an emission of an X-Ray photon. This process is *called* X-ray fluorescence (XRF) [2–6].

The energy of the emission i.e. the wavelength is characteristic of the atom (element) from which it originated while the intensity of the emission is related to concentration of the atoms in the sample [7].

The high temperature inductively coupled plasma has been successfully used as an effective ion source for a mass spectroscopy, the type of method of inductively coupled plasma-mass spectroscopy (ICP-MS) is routinely used for measurements of trace elements in clinical and biological samples [8, 9].

*Modern Spectroscopic Techniques and Applications*

associated with transitions between those levels.

*arrows indicate absorption or emission of light.*

frequency is showed by the equation below:

υ = \_c

<sup>Ε</sup> = \_

this is understood as AAS (**Figure 1a**).

be measured with a detector, this is AES.

where c is the speed of light and λ the wavelength. Thus,

light as the atom returns to the ground state i.e. AFS (**Figure 1c**).

This process is *called* X-ray fluorescence (XRF) [2–6].

trace elements in clinical and biological samples [8, 9].

concentration of the atoms in the sample [7].

following equation:

**Figure 1.**

or ground state (E0), or at any of a group of excited states depending on how many electrons have been jumped to higher energy levels (E′') although it is normal to think for the first transition. Each element has a unique energy level and the ΔEs

*Energy level diagrams to show transitions associated with (a) AAS, (b) AES, and (c) AFS. The vertical* 

The ΔE for movements of *valence* electrons in most elements meets the energy equal to UV/visible radiation. The energy of a photon (E) is computed with the

where h is Planck's constant (6.63 × 10<sup>−</sup>34 Js) and υ the frequency of the waveform corresponding to that photon. The relationship between wavelength and

hc

Under appropriate circumstances, outer shell electrons of vaporized atoms may be excited by heating. As these electrons return to the more stable ground state, energy is lost. As **Figure 1b** shows, some of this energy is emitted as light, which can

Some of the radiant energy absorbed by ground state atoms can be emitted as

When high-energy photons strike to a massive particle, it can excite an inner shell electron of the atom. The forming inner orbital vacancy can be filled with an outer shell electron. The transition is created by an emission of an X-Ray photon.

The energy of the emission i.e. the wavelength is characteristic of the atom (element) from which it originated while the intensity of the emission is related to

The high temperature inductively coupled plasma has been successfully used as an effective ion source for a mass spectroscopy, the type of method of inductively coupled plasma-mass spectroscopy (ICP-MS) is routinely used for measurements of

and a specific transition, ΔE, is associated with a unique wavelength. When light of a specific wavelength enters an analytical system, outer shell electrons of the corresponding atoms will be excited as energy is absorbed. As a result, the amount of light transmitted from the system to detector will be reduced,

E = hυ (1)

<sup>λ</sup> (2)

<sup>λ</sup> (3)

**2**

It follows from Eqs. 1–3 that the wavelengths of the absorbed or emitted light are unique to a given element.
