Analytical Flashcards
What is flight mass spectrometry
Where the elements in a compound are discovered via their mass
What are the stages of mass spec
Vaporisation
Ionisation
Acceleration
Time of Flight
Detection
What is vaporisation in mass spec
Dissolve the sample in a volatile solvent
Reduces pressure
What is ionisation in mass spec
Bombard sample with high energy elections, knocking off electrons to form 1+ charge
Fragmentation May also occur
What is acceleration in mass spec
Using the electric field to accelerate ions to give them equal kinetic energy
What is the equation for kinetic energy
Ke = 1/2 x m x v(squared)
What is time of flight in mass spec
Ions with different masses travel with different velocities
How does Carbon 13 NMR work
The difference in magnetic field between an atom with odd numbers of electrons and a large magnetic field can be measured by the absorption of radio waves to flip the nucleus
What atoms can be detected by NMR
H, C13
Why is a solvent used in NMR
To dissolve the organic substance without interfering with the spectrum
What are two commonly used NMR solvents
CCl4 (tetrachloromethane)
CDCl3 (deuterated brichloromethane)
How is NMR calibrated
The use of tetramethylsilane (TMS) creates a single peak at 0, so all other peaks are positioned relative to it
Why is TMS used
Generates a single peak in C13 and H NMR
Peak lies to right hand side of spectrum
Unreactive
Low boiling point so easy to remove from sample
Non toxic
What is the formula of TMS
C4H12Si
What does the number of peaks in C13 NMR tell us
The number of different carbon environments
What affects the height of peaks in C13 NMR
The more C atoms in that environment, the higher the peak
What does the position of peaks tell us in C13 NMR
The type of chemical environment
What does the number of signals in proton NMR show us
The number of hydrogen environments
What does the intensity of the peak show in proton NMR
The number of hydrogen atoms in the environment
What does the chemical shift(position of peak) show
The type of chemical environment
What is the reference chemical for proton NMR
TMS
What does the shape of peaks show in proton NMR
The number of adjacent hydrogens
How can high resolution NMR chemical shift be calculated
Field for TMS - field of sample/ field for TMS x 10-6 ppm
How does high resolution proton NMR differ from other NMR
Signals in high res H1 NMR are split, caused by the interactions of magnetic fields on hydrogen ions in neighbouring carbon atoms
What rule dictates the number of lines a signal is split into
Hydrogens on neighbouring atoms + 1
What determines retention time in gas chromatography
The higher the affinity for the stationary phase, the longer the retention time
What is the acidified dichromate test
Tests for alcohol
What is the result of the potassium dichromate test
Orange to green in presence of an alcohol
What alcohols turn green on the addition of potassium dichromate
Primary and Secondary
How does the Schiffs reagent test work
Warm the reaction mixture, then pass the vapours through cold Schiffs reagent
What are the results of Schiffs reagent
If Schiffs reagent turns magenta, it is a primary alcohol, if there’s no colour change it’s a secondary alcohol
What is the stationary phase for thin layer chromatography
Silica plate
What is the mobile phase for thin layer chromatography
Liquid solvent
What is the stationary phase for paper chromatography
High quality filter paper
What is the mobile phase for paper chromatography
Liquid solvent
What affects the rate at which a substance moves up the plate in TLC
Solubility of substance in solvent
Attraction between solute and stationary phase
What is the use of a watch glass in TLC
Prevents evaporation of solvent
What must the pencil be in TLC
Insoluble so as not to affect the results
Where must the solvent level be in TLC
Solvent level below the pencil line to prevent washing off substance
