Atomic absorption spectroscopy

Atomic absorption spectroscopy

1. Atomic Absorption S pectroscopy Miss Ayesha shafi

2. Contents Introduction Principle Theory Instrumentation Applications

3. Introduction Atomic Absorption Spectroscopy is a very common technique for detecting metals and a few non-metal in samples It is very reliable and simple to use. It can analyze over 62 elements. It also measures the concentration of metals in the sample.

4. HISTORY: The first atomic absorption spectrometer was built by CSIRO scientist Alan Walsh in 1954. Shown in the picture Alan Walsh(left), with a spectrometer.

5. Elements detectable by atomic absorption are highlighted in pink in this periodic table

6. TYPES OF ATOMIC SPECTRA 1) ATOMIC EMISSION SPECTRA:

7. 2) ATOMIC ABSORPTION SPECTRA:

8. 3 ) ATOMIC FLUORESCENCE SPECTRA

9. COMPARISON

10. The technique uses basically the principle that free atoms (gas) generated in an atomizer can absorb radiation at specific frequency. Atomic-absorption spectroscopy quantifies the absorption of ground state atoms in the gaseous state . The atoms absorb ultraviolet or visible light and make transitions to higher electronic energy levels. The analyte concentration is determined from the amount of absorption. PRINCIPLE OF AT OMIC ABSORPTION SPECTROSCOPY

11. THEORY OF ATOMIC ABSORPTION SPECTROSCOPY Atomic absorption spectroscopy is a method of elemental analysis. When a solution containing the metallic species is introduced into a flame, the vapours of metallic species will be obtained. Some of the metal atoms may be raised to an energy level sufficiently high to emit the characteristic radiation of the metal during their return but a large percentage of metal will remain in the non-emitting ground state. T hese ground state elements are receptive of light radiation of their own specific wavelength. Thus when a light of this wavelength is allowed to pass through a flame having atoms of metallic species, part of light is absorbed and the absorption is directly propotional to the density in the flame. It is particularly useful for determining trace metal in liquids and is almost independent of molecular form of the metal in the sample. The method is very sensitive and can detect the different metals in concentration as low as and one frequently lower than 1 ppm. A disadvantage of the method is that only one element can be determined at a time. This method has limited use in quantitative analysis.

12. THEORY OF ATOMIC ABSORPTION SPECTROSCOPY .

13. The total amount of light absorbed may be given mathematically by the following expressions : Total number of light absorbed = πe 2 /mc Nf Where, e = is the charge on the electron of mass m = mass of electron c = is the speed of light N = is the total number of atoms that can absorb at frequency in the light path v = frequency f = is the oscillator strength or ability of each atom to absorb at frequency π = is constant The above equation can be written as : Total amount of light absorbed= Constant x N x f THEORY OF ATOMIC ABSORPTION SPECTROSCOPY

14. INSTRUMENTATION OF ATOMIC ABSORPTION SPECTROSCOPY

15. I nstrumentation Atomic absorption spectrophotometer based on the following components. Source Atomizer Monochromator Detector Read out devise

16. Radiation Source The main radiation sources are used for the atomic absorption are following. Hollow cathode lamp (HCL) Electrode less discharge lamp (EDL) Hollow cathode lamp : It consist of tungsten anode and a cylindrical cathode sealed in a glass tube filled with neon or Argon at a pressure of 1-5 torr. When a potential of 300V is applied, ionization of inert gas occur and a current of 5-20mA is generated as ions.

17. Hollow Cathode lamp: A portion of the sputtered metal atoms is in excited states and thus emit their characteristics radiation as they returns to the ground state.

18. Electrode less Discharge L amp A typical lamp is constructed from a sealed quartz tube containing a few torr of an inert gas such as argon and a small quantity of the metal whose spectrum is of interest. The lamp contain no electrode but instead is energized by an intense field of radiofrequency or microwave radiation.

19. SOURCE MODULATION Used to eliminate the interferences caused by emission of radiation by the flame. For these, output of the radiation source is modulated so that the intensity fluctuates at a constant frequency . An easy way to eliminate the emission from the source is to interpose a circular metal disk or chopper in the beam between the source and the flame.

20. Atomizers The process of converting an analyte in solid, liquid or solution form to a free gaseous atom is called as the atomization and the instrument used for this purpose is called as the atomizers. Two types of the atomizers are used. A) flame atomizer B) E lectrothermal atomizer

21. Flame atomizer In flame atomizer, the sample is first converted into a fine mist consisting of small droplets of solution. It is accomplished by using a nebulizer assembly. The sample is aspirated into a spray chamber by passing a high pressure stream consisting of one or more combustion gases, part the end of a capillary tube immersed in the sample. The impact of the sample with the glass impact head produces an aerosol mist. The aerosol mist mixes with the combustion gases in the spray chamber before passing to flame which desolvates the aerosol mist to a dry aerosol of small solid particles.

22. Subsequently, flame thermal energy volatilizes the particles, producing a vapors consisting of molecular species, ionic species and free atoms. Thermal energy in flame atomization is provided by the combustion of a fuel –oxidant mixture.

23. SEQUENCE OF STEPS IN A FLAME ATOMIZER SAMPLE NEBULIZER ASSEMBLY CONVERSION INTO FINE MIST & SMALL DROPLETS OF SOLUTION ASPIRATED INTO SPRAY CHAMBER (MIXING CHAMBER) AEROSOL MIXES WITH COMBUSTION GASES FLAME (ATOMIZATION OCCURS)

24. Atomization occurs A thin Flame is produced Mixture is carried to the flame NEBULIZER CONSTRUCTION:

25. Fuel Oxidant Temperature, o C Maximum Burning Velocity (cm s -1 ) Natural Gas Air 1700-1900 39-43 Natural Gas Oxygen 2700-2800 370-390 Hydrogen Air 2000-2100 300-440 Hydrogen Oxygen 2550-2700 900-1400 Acetylene Air 2100-2400 158-266 Acetylene Oxygen 3050-3150 1100-2480 Acetylene Nitrous Oxide 2600-2800 285 FUELS & OXIDANTS USED FOR FLAME COMBUSTION

26. Flame Structure

27. Flame atomizers Flame atomizers are of two types Continuous Discrete Continuous: the sample is fed into atomizer at a constant rate. The spectral line is then constant with time. Discrete: A measured quantity of the sample is introduced as a plug of liquid or solid. T he spectral line is rises to a maximum and then decreases to zero.

28. Electro thermal A tomizers A typical electro thermal atomizer also known as graphite furnace, consisting of a cylindrical graphite tube approximately 1-3 cm in length and 3-8 mm in diameter. The graphite tube is housed in an assembly that seals the end of the tube with optically transparent windows. The assembly also allows for the passage of continuous stream of inert gas, protecting the graphite tube from oxidation and removing the gaseous products produced during atomization. A power supply is used to pass a current through the graphite tube, resulting in resistive heating.

29. Construction of electro thermal atomizers .

30. Electro thermal Atomizers Samples between 5 and 50 micro liter are injected into the graphite tube through a small diameter hole located at the top of the tube. Atomization takes place in three stages:

31. Electro thermal Atomizers In the first stage sample is dried by using a current that raises the temperature of the graphite tube to about 110 ◦ C and desolvation leaves the sample as a solid residue. In the second stage, which is called as the ashing , the temperature is increased to about 350-1200 ◦ C. At this temperature the sample is converted into the carbon dioxide and water and volatile inorganic material are vaporized. These gases are removed by the inert gas flow. In the final stage, the sample is atomized by rapidly increasing the temperature to 2000-3000 ◦ C. Three stages are completed in 45-90 sec. The analyte concentration in the resulting vapor phase may be as much as 1000 times greater than that produced by flame atomization.

32. Instrumentation (continues) Monochromators: Monochromators are used to isolate the narrow band width of wavelength that are absorbed by the metals. Detectors: the photomultiplier is used to detect the light absorbed by the analyte. It is same as described in UV/ mass spectrometer.

33. Working of atomic absorption spectrophotometer Single beam atomic absorption spectrophotometer: Single beam measurements are depended upon the varying intensity of a single beam of light having a single optical path. That is why called as single beam AA spectrophotometer . It consist of hollow cathode lamp, a chopper, atomizer and a simple grating spectrophotometer with photomultiplier detector. Double beam atomic absorption spectrophotometer: the beam from the hollow cathode source is split by mirror chopper so that one half passed through the flame and the other half around it. The two beams are then recombined by a half silver mirror and passed into grating monochromator. The photomultiplier tube serves as the detector

34. Single beam spectrophotometer:

35. Single / double beam spectrophotometer

36. SAMPLE PREPARATION T the preparation of the sample solution for a solid material is most time consuming step of process of analysis in an atomic absorption spectroscopy. It involves following steps ;

37. Pharmaceutical Biological Biochemical For detection of purity and consistency of these trace metals Also for quantitative determination of metals mainly in solid sample as mineral, ores and alloys For Quantitative & Qualitative Analysis: Apllication of atomic absorption spectroscopy

38. Magnesium in cast iron Silver, Zinc, Copper and Lead in Cadmium metal Determination Of Trace Copper In Nickel Metal Method of multiple standard addition A plot of absorbance against the amount of standard can be used to determine the amount of copper in a sample. ASSAYS OF TRACE METALS

39. Determination of trace metal in a silicon foam cavity wound dressing Zinc in Zinc insulin suspension and tetracosactrin Zinc injection Copper and Iron in ascorbic acid Aluminum in albumin solution and Ca, Mg, Mercury Zinc in water used for diluting haemodialysis solution BIOLOGICAL & BIOCHEMICAL ANALYSIS

40. For the analysis of pharmaceutically or therapeutically essential component of formulation, such as Zinc in Zinc-insulin, minerals in multivitamin-mineral preparation and Ca, Mg, Al in antacids. To establish concentration limits where the metal is regarded as an impurity. PHARMACEUTICAL ANALYSIS

41. Mining industries Petroleum industries Determination of metallic elements in food industry like Copper, Zinc and Nickel in vegetable oil and copper in beer. INDUSTRIAL ANALYSIS