1. 427 PHC

2. Introduction

3.  Spectrometric methods are a large group of analytical methods that are based on atomic and molecular spectroscopy.  Spectroscopy is the science that deals with the interactions of radiation with matter.  The most widely used spectrometric methods are based on electromagnetic radiation (light, gamma rays, X-rays, UV, microwave, and radio- frequency).

4. Electromagnetic spectrum

5. some of the properties of different wavelengths of electromagnetic radiation.

6. Absorption of Radiation  When radiation passes through a layer of solid, liquid, or gas, certain frequencies may be absorbed, a process in which electromagnetic energy is transferred to the sample.

7.  Absorption promotes these particles from their ground state to more higher-energy excited state.

8.  Tow types of absorption spectra:  Atomic absorption spectrum.  Molecular absorption spectrum.

9. Beer’s Law  Many compounds absorb radiation. The diagram below shows a beam of monochromatic radiation of radiant power P 0 directed at a sample solution.  Absorption takes place and the beam of radiation leaving the sample has radiant power P.

11.  The amount of radiation absorbed may be measured in a number of ways:  Transmittance, T = P / P 0 % Transmittance, %T = 100 T  Absorbance,  A = log 10 P 0 / P A = log 10 1 / T A = log 10 100 / %T A = 2 - log 10 %T

12.  The last equation, A = 2 - log 10 %T, is worth remembering because it allows you to easily calculate absorbance from percentage transmittance data.  The relationship between absorbance and transmittance is illustrated in the following diagram:

13.  The equation representing the Beer’s law: A = ε b c  Where  A is absorbance (no units, A = log 10 P 0 / P ).  ε is the molar absorbtivity (is a measure of the amount of light absorbed per unit concentration) with units of L mol -1 cm -1.  b is the path length of the sample that is, the path length of the cuvette in which the sample is contained. We will express this measurement in centimeters.  c is the concentration of the compound in solution, expressed in mol L -1.

14.  Beer’s law tells us that absorbance depends on the total quantity of the absorbing compound in the light path through the cuvette. If we plot absorbance against concentration, we get a straight line passing through the origin (0,0).

15. Atomic Specrtoscopy

16. Introduction:  Atomic spectroscopy is based upon absorption, fluorescence, or emission of electromagnetic radiation by atoms or ions.  The sample is decomposed and converted to atoms by means of an atomization process.  The resultant spectra are simple and consist of a no. of narrow and discrete lines

17. Classification of Atomic Spectroscopy:  The next table categorizes the atomic spectroscopic methods on the basis of the atomization technique.

18. Common NameBasis of methodAtomization temperature, C o Atomization method Atomic absorption Spec.Absorption1700-3150Flame Atomic emission spec.Emission Atomic fluorescence spec.Fluorescence Electrothermal atomic absorption spec. Absorption1200-3000Electrothermal Electrothermal atomic fluorescence spec. Fluorescence Inductively coupled plasma spectroscopy Emission6000-8000Inductively coupled argon plasma

19. Advantages:  Highly specific.  Wide application.  Excellent sensitivity (ppm-ppb).  Speed.  Convenience.

20. Atomic Absorption Spectroscopy AAS

21. Introduction

22.  AAS is the study of the absorption of radiant energy by atoms.  It is a technique for determining the concentration of a particular metal in a sample.  Atomic absorption spectroscopy dates to the nineteenth century, and the modern form was largely developed during the 1950s.

23. Elements that are highlighted in pink are detectable by AAS

24.  Although the atomic absorption spectrometry is quite expensive, the technique is very wide-spread, due to the fact that by AAS it is possible to determine about 70 elements (mainly metals) at very low concentrations.

25. Basic Principle

26.  In AAS, the sample solution is first vaporised and atomized in a flame, transforming it to unexcited ground state atoms, which absorb light at specific wavelengths.  A light beam from a lamp whose cathode is made of the element in question is passed through the flame. Radiation is absorbed, transforming the ground state atoms to an excited state.

28.  The amount of radiation absorbed depends on the amount of the sample element present.  Absorption at a selected wavelength is measured by the change in light intensity striking the detector and is directly related to the amount of the element in the sample.

29.  Only a light with a specific wavelength belongs to each of these metals and when this light is absorbed it is missing from the spectra of the electromagnetic radiation and a black line appears in the absorption spectrum of the atom.

31. Operation principle of an atomic absorption spectrometer.

32. Thank You