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Summary Metric: Key concepts required for the exam.

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This is a complete, concise set of exam revision notes for all courses covered in the Metric module including mathematical tools A/B, separation science, measurement and statistics, biological chemistry and physics for chemists. It was made using both lecture notes and exam model answers. D...

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  • March 23, 2021
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METRIC: KEY CONCEPTS FOR EXAM



SEPARATION SCIENCE

TLC (Thin layer chromatography)

 Mobile phase: suitable liquid solvent, ascends plate via capillary action
 Inert plate coated with stationary phase: silica gel, polar Si-OH bonds, alumina gel
 Polar molecules interact strongly, elute slower.
 Conjugated systems: UV light
 Unsaturated systems: Iodine
 Ninhydrin: Amino acids
 DNP: Aldehydes/ketones
 Vanillin: general stain
 PMA: universal stain
 Rf value = (distance travelled by solute) / (distance travelled by solvent)
 Dissolve sample in volatile solvent e.g., DCM
 Compounds travel further up the plate if a more polar solvent is used

GC – FID

 Gas chromatography – flame ionisation detection
 Gas inlets/flow controller : controls the flow of mobile phase/carrier gas through the
instrument
 Autosampler: introduction of precise volume of sample
 Inlet: vaporisation of the sample, and mixing with the carrier gas can be split or splitless
 Column: contains stationary phase, separation of analytes occurs here
 Column oven: controls temperature of column
 Detector: responds to physiochemical property of the analyte, amplifies the response and
generates an electric signal for the data system to produce a chromatogram
 Data system: receives analogue signal from the detector and digitalises it to form the record
of chromatographic separation known as the chromatogram , sample identification and
quantitation

Components of a HPLC instrument

 HPLC column – separation of analytes
 Detector – measures physiochemical property of analyte/mobile phase as it elutes from the
column
 Autosampler – introduces reproducible amounts of sample into the HPLC element stream
 Mobile phase reservoir – supply of mobile phase
 Pumping system – delivery of mobile phase of desired composition, continuous and pulse
free to HPLC system

How HPLC time can be reduced

 Shorter column length
 Smaller particles in column
 Increase mobile phase flow rate
 Decrease column diameter

Melting points

 Melting point range: time from which first drop of liquid appears until the entire sample has
melted
 Should be within 2 degrees if pure

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