Spectroscopy Lecture 4 Ahmad Razali Bin Ishak Department of Environmental Health Faculty of Health Sciences UiTM Puncak Alam

Spectroscopy The study how the chemical compound interacts with different wavelengths in a given region of electromagnetic radiation The collection of measurements signals (absorbance) of the compound as a function of electromagnetic radiation is called a spectrum. Important to understand EMR and its components before we study spectroscopy

EMR According to wave property, EMR consisted of oscillating electric and magnetic fields that propagate through space in a straight line (unless refracted or reflected) with a constant velocity Has a various fundamental properties such as wavelength, wave number, frequency, velocity Self reading (properties of EMR in details)

Properties of EMR V = Wave Number (cm -1 )  Wave Length C = Velocity of Radiation (constant) = 3 x cm/sec.  = Frequency of Radiation (cycles/sec) The energy of photon: h (Planck's constant) = 6.62 x C = 

Energy absorption The mechanism of absorption energy is different in the Ultraviolet, Infrared, and Nuclear magnetic resonance regions. However, the fundamental process is the absorption of certain amount of energy. The energy required for the transition from a state of lower energy to a state of higher energy is directly related to the frequency of electromagnetic radiation that causes the transition.

Spectroscopy- Naming system Spectroscopy- Interaction of EMR & matter Naming- on basis of either EMR or matter involved E.g. o UV spectroscopy: EMR involved is UV and the matter involved is electron o NMR spectroscopy: EMR –radio frequency: matter-Nucleus o IR-Spectroscopy: EMR-IR -Matter-Bond of molecules

Different types of Spectroscopy UV-Vis Spectroscopy IR Spectroscopy Mass Spectroscopy NMR Spectroscopy Atomic Spectroscopy Inductive couple plasma Atomic Emission Spectroscopy

Group Assignment Pick ONE type of spectroscopy above. Prepare an assignment not more than 5 pages. Please include all the followings in your assignment 1.Introduction 2.Principle and theory 3.Picture and schematic diagram 4.Application 5.References Submission date : Before 3 rd Seminar

Lecture 5 Atomic Absorption Spectroscopy Ahmad Razali Bin Ishak Department of Environmental Health Faculty of Health Sciences UiTM Puncak Alam

Introduction In analytical chemistry, Atomic absorption spectroscopy is a technique for determining the concentration of a particular metal element in a sample. Atomic absorption spectroscopy can be used to analyze the concentration of over 62 different metals in a solution.

Applications of AAS water analysis (e.g. Ca, Mg, Fe, Si, Al, Ba content) food analysis analysis of animal feedstuffs (e.g. Mn, Fe, Cu, Cr, Se,Zn) analysis of additives in lubricating oils and greases (Ba,Ca, Na, Li, Zn, Mg) analysis of soils clinical analysis (blood samples: whole blood, plasma, serum; Ca, Mg, Li, Na, K, Fe)

Principles of AA. The metal vapor absorbs energy from an external light source, and electrons jump from the ground to the excited states

Cont.. The ground state atom absorbs light of the same characteristic wavelengths as it emits when returning from the excited state to the ground state. The intensity of the absorbed light is proportional to the concentration of the element in the flame - quantitative analysis A calibration curve can thus be constructed [Concentration (ppm) vs. Absorbance]

Hollow cathode lamp PMT Flame sample nebulizer Air Acetylene Coating of element Schematic diagram AA Spectrometer monochrometer

The light The light that is focused into the flame is produced by a hollow cathode lamp. Inside the lamp is a cylindrical metal cathode containing the metal for excitation, and an anode. When a high voltage is applied across the anode and cathode, the metal atoms in the cathode are excited into producing light with a certain emission spectrum.

Cont.. The type of hollow cathode tube depends on the metal being analyzed. For analyzing the concentration of copper in an ore, a copper cathode tube would be used, and likewise for any other metal being analyzed. The electrons of the atoms in the flame can be promoted to higher orbitals for an instant by absorbing a set quantity of energy (a quantum).

Atomization The technique typically makes use of a flame or graphite furnace to atomize the sample Three steps are involved in turning a liquid sample into an atomic gas: Desolvation – the liquid solvent is evaporated, and the dry sample remains Vaporization – the solid sample vaporizes to a gas Volatilization – the compounds making up the sample are broken into free atoms.

Flame The flame is arranged such that it is laterally long (usually 10cm) and not deep. The height of the flame must also be monitored by controlling the flow of the fuel mixture. A beam of light passes through this flame at its longest axis (the lateral axis) and hits a detector.

Nebulizer Sucks up the liquid sample (= aspiration) creates a fine aerosol (fine spray) for introduction into flame mixes aerosol, fuel and oxidant thoroughly, creates a heterogeneous mixture the smaller the size of the droplets produced, the higher the element sensitivity fuel = acetylene oxidant = air (or nitrous oxide)

Monochromator isolation of the absorption line from background light and from molecular emissions originating in the flame, i.e. tuned to a specific wavelength multi-element lamps: large number of emitted lines; isolation of the line of interest

A.6.4 Determine the concentration of a solution from a calibration curve.

Sample Problem: pg. 312, #3 Lead is extracted from a sample of blood and analyzed at 283 nm and gave an absorbance of in an AA spectrometer. Using the data provided, graph a calibration curve and find the concentration of lead ions in the blood sample. The data provided in the problem appears in the upper left hand corner of this MS EXCEL worksheet. The graph was used to calculate the best fit line. The equation was then used to calculate the concentration of Pb (II) ions with an absorbance of The result, ppm, is displayed above the graph.

Thank You