Analytical Chemistry Flashcards
definition of partition coefficient
equilibrium constant that relates the concentration of solute between two immiscible solvents
definition of adsorption
bonding of molecules to surface of stationary phase
definition of paper chromatography
components partition between solvent and liquid stationary phase
solvent and stationary phase of paper chrom.
mobile phase (liquid/gas) water trapped in cellulose fibres
describe paper chrom. with non polar solvent
little attraction to -OH groups on cellulose
high Rf value
describe paper chrom. with polar solvent
dissolve more in stationary phase
low Rf value
how to identify colourless substances
ninhydrin spray
describe two way chromatography
Rotate 90 degrees
Re run in a different solvent
definition of thin layer chromatography
Separation depends on the differential adsorption of components onto the solid phase (Al2O3/SiO2)
solvent and stationary phase of thin layer chrom.
mobile phase
Al2O3/SiO2
thin layer chrom in very polar solvent
dissolves more in solvent = high Rf value
what compounds that can hydrogen bond do
adsorb more to solid stationary phase
definition of high performance liquid chromatography
using partition to separate
describe high performance liquid chrom.
non volatile liquid( hydrocarbon) on solid support (silica) = stationary phase
mobile phase of HPLC
polar solvent
what does the detector on HPLC record
retention time= time it takes for component to pass column
what does area under peak show in HPLC
amount of solute out of column
what is HPLC used for
Separate peptides and proteins
Analyse urine samples
Monitoring pollutants
describe gas liquid chromatography
similar to HPLC but gaseous sample
conditions for gas liquid chrom.
same inert carrier gas
flow rate
stationary phase
temperature
limitation of gas liquid chrom.
similar compounds will have similar retention times - new compounds wont have match
how to find percentage composition of mixture by GLC
1/2 x base x height
what is GLC used for
Testing steroids in athletes
Testing fuels used in racing
Analysing blood samples
how does a GLC graph look like
recorder response/time
purpose of NMR
Used to identify hydrogen atoms in different part of the molecule
how does NMR work
nuclear spin from spinning proton produces two spin states
energy absorbed in NMR
can align with or against applied field
why is TMS used as standard reference compound
inert volatile liquid
equivalent hydrogen atom environments
one sharp peak
12 protons in same environment = high frequency
how to find -OH-/-NH- in NMR spectrum
Produce an NMR
Add D2O (doesn’t absorb electromagnetic spectrum, no protons) sample
Rerun NMR
Compare to find the peak that has disappeared = OH/NH peak
why is -OH-/-NH- appear to be a single peak
reacts quickly with water
reaction of -OH- with D2O
OH + D2O ⇌ -OD + HOD
reaction of -NH-CO- and D2O
⇌ -ND-CO- + HOD
what does low resolution NMR show
single peaks for different environment of hydrogen
what does high resolution NMR show
cluster of peaks for each environment and neighbouring hydrogens
how do find neighbouring hydrogens
splitting peaks -1
what does height of peak show
number of hydrogen
what does more down field peak show
closer to electronegative element
describe carbon-13 NMR spectrometry
1% of carbons in compound will be carbon-13 instead of carbon-12
CDCl3 solvent used to prepare sample
formula for double bonds
2n+2 -#H/2
definition of mass spectrometry
Mass spectrometry of an element can be used to measure relative isotopic masses and their relative abundances = calculate relative atomic masses
process of mass spectrometry
Sample is vaporised
Sample bombarded with high energy electrons
Breaks covalent bonds by fragmentation
how are compounds fragmented
primary < secondary < tertiary
where is the molecular mass found in mass spectrometry
last peak
how to find number of carbons using [m+1] peak
(100/1.1) x ([M+1]+1)/M+
percentage of [M+2] and [M] in Cl
35Cl = 75% 37Cl = 25%
percentage of [M+2] and [M] in Br
79Br = 50% 81Br = 50%
when there is two Cl/Br in compound
[M]:[M+2]:[M+4]
two Cl atoms: three peaks with 9:6:1 ratio
two Br atoms: three peaks with 1:2:1 ratio
