Absorcion atomica

ATOMIC ABSORPTION SPECTROPHOTOMETRY COOKBOOK Section 1

Basic Conditions of Analysis of Atomic Absorption SPECTROPHOTOMETRY

Atomic Absorption Spectrophotometer Cookbook Section 1

CONTENTS
1. Principal of Atomic Absorption Spectrophotometer ................................... Why atoms absorb light .......................................................................................Relation between light absorption rate and atomic density .................................... Sample atomization method ................................................................................. a) b) 2. Flame atomic absorption ................................................................................. Electro-thermal atomic absorption................................................................... 1 1 2 3 3 5 9 9 9

1.1 1.2 1.3

Basic Condition for Analysis ............................................................................ Conditions of equipment ...................................................................................... a) b) c) Analysis line ....................................................................................................2.1

Slit width ........................................................................................................ 13 Lamp current value ......................................................................................... 14 Analysis conditions of flame atomic absorption .................................................... 15 Flame selection............................................................................................... 15 Mixing ratio of oxidant and fuel gas ................................................................ 17 Beam position in flame .................................................................................... 17 Analysis conditions of electro-thermal atomic absorption ..................................... 18 Drying condition............................................................................................. 18 Ashing condition ............................................................................................. 19 Atomizing condition ........................................................................................ 21 Sample injection quantity................................................................................ 23

2.2 a) b) c) 2.3 a) b) c) d)

1.

Principal of Atomic Absorption Spectrophotometer Why atoms absorb light The atomic absorption spectrometry uses absorption of light of intrinsic wavelengths by atoms. All atoms are classified into those having low energies and those having high energies. The state having low energies is called the ground state and the state having highenergies is called the excited state. The atom in the ground state absorbs external energies and is put in the excited state. For example, sodium is mainly in two excited states, having higher energies by 2.2eV and 3.6eV respectively than in the ground state, as shown in Fig. 1.1. (eV is a unit to measure energies and is called an “electron volt”.) When 2.2eV energy is given to the sodium atom inthe ground state, it moves up to the excited state in (I) and when 3.6eV energy is given, it moves up to the excited state in (II). Energy is given as light, and 2.2eV and 3.6eV respectively correspond to energy of light at 589.9nm and 330.3nm wavelength. In the case of sodium in the ground state, only light of these wavelengths are absorbed and no other wavelength light is absorbed at all.

1.1Fig. 1.1 Sodium energy states The difference between energies in the ground state, and in the excited state is fixed by the element and wavelength of light to be absorbed. Atomic absorption spectrometry uses the hollow cathode lamp (HCL). The HCL gives off light characteristic to the elemental wavelength being measured. Thus, the light absorbed measures the atomic density. 1.2 Relation between...