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International University-Vietnam National University School of Bio-technology

International University-Vietnam National University School of Bio-technology. SPECTROCOPIC METHOD. Course: Analytical Chemistry Lecture: Dr Khoi Date: 18/4/2011. OUTLINE. OVERVIEW OF SPECTROSCOPIC ANALYSIS LIGHT PRINCIPLE OF SPECTROSCOPY Spectroscopy based on absorption

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International University-Vietnam National University School of Bio-technology

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  1. International University-Vietnam National UniversitySchool of Bio-technology SPECTROCOPIC METHOD Course: Analytical Chemistry Lecture: Dr Khoi Date: 18/4/2011

  2. OUTLINE • OVERVIEW OF SPECTROSCOPIC ANALYSIS • LIGHT • PRINCIPLE OF SPECTROSCOPY • Spectroscopy based on absorption • Spectroscopy based on emission • BASIC INSTRUMENTS • SUMMARY

  3. I. OVERVIEW OF SPECTROSCOPIC ANALYSIS • Definition: The term Spectroscopy refers to a branch of science which utilizes the interaction between electromagnetic radiation with matter. • Purpose of Spectroscopic analysis: A powerful tool for qualitative and quantitative analysis: - Identifying substances through their absorption and emission spectrum - Identifying the concentration or amount of a given chemical (atomic, molecular, or ionic) species.

  4. II. LIGHT • What is the light? - Light is a form of radiant energy. • What is electromagnectic- radiation (EMR)? - Electromagnetic radiation is a form of energy whose behavior is described by the properties of both waves and particles.

  5. Electric currents could give rise to magnetic fields and vice versa.  electromagnetic radiation can be described as a train of electric and magnetic fields that oscillate perpendicularly to each other. (1)Michael Faraday's discovery

  6. The wave properties • Wave properties: Electromagnetic radiation is a type of energy that is transmitted space at enormous velocity.(2.99792×108 m/s) - Amplitude: the length of electrical vector as maximum in the wave. - Wavelength: the distance between successive maxima, or successive minima of an electromagnetic wave. - Frequency: the number of oscillations of an electromagnetic wave per second (v).

  7. The wave properties

  8. The particle properties: - We assume that electromagnetic radiation consists of a beam of energetic particles called photons. - The energy of a photon, in joules, is related to its frequency, wavelength, by the following equations - Where h is Planck’s constant, which has a value of 6.626 × 10–34 J /s.

  9. Interaction between light and matter - The nature of interaction between light and matter is the interaction between an electron with a photon. - An electron that absorbs a photon will gain energy of the light wave and change their energy state.

  10. III. Principle of spectroscopy • Spectroscopy based on absorption • Spectroscopy based on emission

  11. Transmittance and Absorbance Beer’s law Application Molecule absorption Atomic absorption Spectroscopy based on absorption

  12. What is the absorption?

  13. 1. Transmittance and absorbance The transmittance (T) %T = x 100% Where: • P0: the radiant power from the source • P : the radiant power transmitted by the sample

  14. The absorbance (A): Example: Calculation the absorbance of a solution having % T of 89 at 400nm.

  15. Solution We have: % T= T x 100% So: T= 89/100 = 0.89 The absorbance of a solution is: A= -log (T) = -log(0.89) = 0.051

  16. 2.Beer’s law so:The main formula: • A: absorbance • a: absorptivity ((L/g.cm) • b: pathlength (cm) • c: concentration (g/L) • A = εbc • ε : molar absorptivity (L/mol.cm)  To calculate the concentration of absorption solution A = abc

  17. Example : Determine the absorptivity A solution contains 4.50 ppm of a colored species . It is found to have an absorbance of 0.3 at 530nm in a 2.00 cm cell.

  18. 3.Molecular absorption • An absorption spectrum

  19. Solvent can affect the appearance of a spectrum • Solvent effect

  20. 4.ATOMIC ABSORPTION SPECTROCOPY • Definition: The absorption of light to measure the concentration of gas-phase atoms.

  21. Sample lightWavelength selector  resonance lines  detector  Determine the amount of element contained within a sample.

  22. Ex: Flame test for sodium ions

  23. 5.Application of absorption • Why is the ocean blue?

  24. Emission of EMR Atomic emission Application Spectroscopy based on emission

  25. What is emission? • Definition:

  26. 1 2 3 Line spectrum Continuum spectrum Emission Spectrum Band spectrum

  27. Atomic EmissionSpectroscopy

  28. Sample  Source  Light  Wavelength selector  Spectral line  Detector  determine the elements contained in the sample

  29. INSTRUMENT OF OPTICAL SPECTROSCOPY I. BASIC COMPONENTS OF SPECTROSCOPIC INSTRUMENTATION II. SPECIFIC TYPES OF SPECTROSCOPIC INSTRUMENTATIONS

  30. BASIC COMPONENTS OF SPECTROSCOPIC INSTRUMENTATION I. SOURCES OF ENERGY II. WAVELENGTH SELECTION III. DETECTORS IV. SIGNAL PROCESSORS

  31. SOURCES OF ENERGY

  32. 1. source of electromagnetic radiation • Provided output including both intense and stable in the desired region • there are two types of electromagnetic radiation source  continuum source, emit radiation over wide range of wavelength.  line source that emits radiation a few selected, narrow wavelength range

  33. 2. source of thermal energy a. flames • use combustion a fuel and an oxidant (2000-3400 K)

  34. b. plasma Is sample cell which excited atoms with temperature from 6,000 to 10,000 K

  35. 3. chemical sources of energy • Bioluminescence using the biological or enzymatic reaction • Chemiluminescence obtained emission by using chemical

  36. WAVELENGTH SELECTION

  37. Common characteristics 1. Nominal wavelength ( effective bandwidth) • Provide a higher resolution using to qualitative the analyte 2. Maximum throughput of radiation • more photons pass through the wavelength selector giving stronger signal applying to quantitative the analytes ( lower resolution)

  38. 1. wavelength selection using filter • used to isolating the narrow band of radiation a. absorption filter • Work by selectively absorbing radiation from a narrow region of electromagnetic spectrum produced narrower effective bandwidth

  39. b. interference filter • Apply to constructive and destructive interference to isolate a narrow range of wavelength • Disadvantage do not allows to continuous selection of wavelength

  40. 2. wavelength selective using a monochromators • Provide for continuous variation of wavelength • Based on rotating of diffraction grating that used to determine what wavelength exits from monochromatic

  41. 2.1. CLASIFICATION • There are two kinds of diffraction grating 1. Fixed-wavelength • selected by manually rotating the grating (measure one or two wavelengths)

  42. Fixed-wavelength

  43. 2.1. CLASIFICATION 2. Scanning • a drive mechanism that continuously rotate the grating • Transformed from polychromatic to monochromatic • Detector converts light power to an electrical signal

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