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- Analytic techniques are important part of chemistry as it helps chemist to conduct qualitative and quantitative analysis on various chemicals
- Classic methods consist of separation like precipitation, extraction, distillation etc...
- Modern methods are mentioned in topic 9 and 17 for Edexcel A-level Chemistry
Gas Chromatography
- Tiny amount of the sample is injected into the chromatography column
- Sample is vaporized and carried through the column by the flow of inert gas
- The column contains a liquid ---> stationary stage and it is adsorbed onto the surface of an inert solid
- the components of the sample separate due to them traveling at different speeds ---> reaching the detector
- A flame ionizer burns the separated gases and measures the electrical conductivity of ions present
High Performance Liquid Chromatography (HPLC)
Normal Phase HPLC
- The column is filled with tiny polar silica particles
- non-polar solvent
- Components in sample are separated according to their differences in polarity/retention time
- Retention time: time needed for the components to be eluted out from the column
- Polar molecules in sample will stick to the polar silica, thus longer time retention time
- Non-polar molecules will run through column more quickly, shorter retention time
Reverse phase HPLC
- The column is filled with tiny non-polar silica particles
- polar solvent
- In reverse, polar molecules in sample have strong attraction to the polar solvent, thus shorter time retention time
- Non-polar molecules will run through column more slower as it is attracted by the non-polar silica, longer retention time
Microwaves
- A radiation with lower energy and shorter wavelength (Radio waves < Microwave < Infrared radiation)
- Microwave radiation creates an electric field which causes polar molecules to line up with the field
- The field switches to the opposite direction so the molecules swivel round to line up again
- Energy in the microwaves is converted to thermal energy
- can be used to separate compounds that dissolved in a solvent (dissolution)
- other uses involve hydrolysis of organic/inorganic compounds, complex metal ions formation etc...
Infrared Spectroscopy
Vibrational modes of molecules (>=2 atoms)
- Symmetrical stretching
- Asymmetrical stretching
- Scissoring
- Rocking
- Wagging
- Twisting
Mechanism
- Molecules absorb infrared radiation which causes the bond to vibrate in various modes
- Different bonds require different amounts of energy to cause vibrations
- Not all molecules are IR active – suitable for those molecules that change their dipole moment & heteronuclear (mostly polar molecules)
- e.g. H2O, CO2, HCl, CO...
- Mainly used for functional groups analysis in organic molecules
Proton Nuclear Magnetic Resonance Spectroscopy (H-NMR)
- Uses electromagnetic and radio frequencies and determine the chemical environment that hydrogen are in for target compound
- Every nuclei in atom has their own spin and are electrically charged
- The energy requires to change the alignment of magnetic nuclei will be measured in external magnetic field
- The energy involved vary as the chemical environment differs for each hydrogen atom
- position of hydrogen can be deduced by studying the signal intensity, couplings and chemical shifts
- mostly used to determine exact structure and connection of atoms in organic compounds

High Resolution NMR
- This splits the peaks into groups of signal ---> multiplets
- This is due to the interaction between protons on neighboring atoms
- n+1 rule: The number of lines on the split pattern for the peak is one more than the number of hydrogen on the adjacent atoms

Low Resolution NMR
- Cannot distinguish individual signals in peaks
- The peaks indicate the different chemical environments of hydrogen
- The area under the peaks correspond to the number of hydrogen in each environment

This is the end of the topic.
