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Methods of analysis and detection

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Name: _____________ OCR A Chemistry 2815/04 Methods of Analysis and Detection 2008 Sherborne School Version 2.0 * Separation techniques of analysis (PC / TLC / GLC / Electrophoresis) * Mass Spectroscopy * Atomic emission spectroscopy * UV / Visible absorption spectroscopy * Combined spectral techniques (NMR / IR / Mass Spectra) By U6F Jacky Huang 2008/03 OR A. Introduction to chromatography All chromatography have the following characteristics: 1. They all have 2 phases, one is a stationary phase and the other one is mobile phase. 2. The dissolved compounds - solutes. 3. There are 2 possible mechanisms, one is partition and the other one is adsorption. In partition: The solutes move between the 2 phases. If it is in the mobile phase, the solutes will moves with it. Therefore, if we do spend more time in the mobile phase, it can move further. In Adsorption: The stationary phase is usually a polar solid and the solutes are polar molecules. The polar molecules will not enter the stationary phase, but it will hold on the surface of the polar stationary phase. B. Paper Chromatography - The most basic chromatography Stationary Phase: Cellulose fiber in the filter paper Mobile Phase: Liquid Solvent In paper chromatography, coloured compounds can be separated into many colours, but in some cases, colourless spots are involved. When this happen, chemicals like NINHYDRIN will be sprayed to those substances, and those substances will form coloured complexes with these coloured compounds. ...read more.


Take a DNA strand 2. Cut - Restriction Enzyme 3. Separated by Electrophoresis 4. Transferred to Nylon membrane 5. P-32 DNA probes bind with DNA band 6. X - Ray exposed, Results. There are also other uses for electrophoresis: Forensic Science / GM Food / Medical Research / Establishing Relationships G. Atomic Emission Spectroscopy - Interaction of EMR This type of spectroscopy concerns the electromagnetic radiation with matter. The EMR have different frequency and different energy. E.g. the radio waves change the orientation of spinning nuclei in a magnetic field and infrared cause's changes in vibrational energy. Calculation for E= h f and C= f ? If a molecule absorbs EMR of 356nm, calculate the energy associated with EMR, directly to the energy gap between E1 and E2 or ?E In the Wave equation we know: C = f ? C = 2.998 x 108 // f = frequency //? = wavelength 2.998 x 108 = f x 3.567 --> f = 8.42 x1014 Hz. This means the energy associated with the EMR --> E =h f E = Energy // h = Plancks' constant = 6.63 x10-34 // f = frequency E = 6.63 x 10-34 x 8.42 x 1014 = 5.58 x 10-19J If we want to calculate the energy for one mole we need to multiply the energy level by the Avogadro constant (6.023 x 1023). E = 5.58 x 10-19 x 6.023 x1023 = 336223.6J = 336kJ mol -1 Explain the Hydrogen absorption/emission spectrum The molecular H (g) ...read more.


If there is n chemically different type of protons next to a particular type of proton then the peak for that proton is split to n+1 peaks Use D2O with -OH group Deuterium is an isotope of hydrogen that does not produce an NMR peak. If an alcohol or carboxylic acid is shaken with D2O, the H of the OH group is replaced by D and the peak disappears from the spectrum. Example of a NMR spectrum - C4H6O2 1. 4 peaks and 4 Cs, 2 of them are in the same environment. 2. The peak just over 50 must be C-O 3. 2 peaks around 130 must be 2 carbons at either end of a C=C. 4. The peak at just less then 170 is the C in a C=O. 5. By using IR and Mass Spectroscopy, we can work out the structural formula. L. Additional Notes and Materials Colour wheel can be used to determine a compounds colour: Colours nm Red 625-740 Yellow 565-590 Green 520-565 Cyan 500-520 Blue 435-500 Magneta 380-435 Colours directly opposite each other on the colour wheel are said to be complementary colours. Blue and yellow are complementary colours; red and cyan are complementary; and so are green and magenta. E.g. Beta-carotene absorbs throughout the ultra-violet region into the violet - but particularly strongly in the visible region between about 400 and 500 nm with a peak about 470 nm and if we use the table above, we know it will absorb blue colour so the colour we will see will between red and yellow. M. ...read more.

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