chromatography ch 13 Flashcards
chromatography
a set of techniques that can be used to separate and analyse the components in a mixture.
How is chromatography performed?
by passing a mixture through a medium (material) that allows the components of the mixture to move through at different rates.
thin layer chromatography (TLC)
similar to paper chromatography, but uses a thin layer of a powder such as alumina spread on a glass plate.
high performance liquid chromatography (HPLC)
a very sensitive type of column chromatography.
It uses very small particles in the column’s solid.
It uses UV to detect the components.
gas chromatography (GC)
A very sensitive technique that uses a gas like nitrogen as the mobile phase.
components
parts of a mixture
the pattern of bans or spots
chromatogram
paper chromatography
chromatography that uses paper as a stationary phase.
column chromatography
a technique in which the stationary phase is in a column.
what states of matter can be a mobile phase?
liquid or gas.
desorption
opposite of adsorption.
molecules come away from the stationary phase.
chroma+ graphy greek)
colour writing
Khromatos + graphos
If a piece of chalk is dipped in ink and then placed in water:
a. what is the stationary phase?
b. what is the mobile phase?
a. the chalk
b. the water
the ability of the mobile phase to stick to the stationary phase, depends on the ______ of the two materials
polarity
the ability of the mixture to dissolve in a solvent depends on the _________ of the mixture and the solvent.
polarity
the rate of movement of each component depends mainly on: (2)
- how strongly the component absorbs onto the stationary phase.
- how readily (easily) the component dissolves in the mobile phase.
why do the components separate in chromatography?
the components bond with the stationary phase and mobile phase in different amounts.
e.g. blue in moves faster because is more soluble in water than the red dye.
A student notices that the blue component of the ink moves faster than the red component.
What does this tell you about the bonding between the blue dye and the paper?
The bonds between the particles of the blue dye bond weakly with the paper, compared to the red dye.
A student notices that the blue component of the ink moves faster than the red component.
What does this tell you about the bonding between the blue dye and the paper vs the red dye and the paper?
The bonds between the particles of the blue dye bond weakly with the paper, compared to the red dye.
If a drop of black ink is placed near the bottom of a strip of paper and is placed in water and left for 30 minutes, a blue band moves quickly down the paper and a red band moves much more slowly.
What does this tell you about the polarity of the blue and red ink?
The blue dye bonds with the water better than the red dye, so it is more polar than the red dye.
Water is a polar solvent so dissolves polar molecules well.
Paper and thin layer chromatography are used for Q_______ analysis.
QUALITATIVE ( what is present, not how much).
Who developed chromatography?
Mikhail Tsvet
origin
the position of the spot of mixture on a paper or thin layer plate.
solvent front
the upper edge of the solvent as it rises up the paper.
calibration curve
a plot of data involving two variables that is used to determine the values for one of the variables.
carrier gas
an unreactive gas , often nitrogen, used in a gas chromatograph.
eluent
the solvent that carries the components and passes through a chromatography column.
injection point
opening through which the sample is injected into a gas chromatograph.
qualitative analysis
an analysis to determine the IDENTITY of the chemical(s) present in the mixture.
quantitative analysis
an analysis to determine the concentration (AMOUNT) of the chemicals present in a mixture
retardation factor
the ratio of the distance a component has moved from the origin to the distance the solvent has moved from the origin.
retention time
the time taken for a component to pass through a chromatography column.
standard solution
a solution that has an accurately known concentration.
Why must the origin be above the level of the solvent?
So that the components move up the paper and not dissolve in the solvent.
What two factors affect how the mixture’s components travel up the paper or column?
- the component’s attraction to the stationary phase.
2. the component’s solubility in the solvent.
What are the two ways a component can be identified?
- Compare unknown to a standard of a known chemical.
e. g. compare unknown to a specific ink chromatgram. - Calculate the retardation factor (Rf) of the sample and compare it to a table of Rf values.
Method 1 Using standards to identify an unknown component.
What do you need to know for this method to be useful?
You must have an idea of what might be present.
These will be the standards you will use.
Why does the standard method require the known and unknown to be on the same paper?
So the rate of movement can be directly compared.
Rf or Retardation factor
distance the solvent front travelled from the origin
Rf values will always be less than ____
1
the component that moves the least, (slowest) has the ________ Rf value.
smallest / lowest value.
The conditions of method 2 must be the same because…
otherwise the unknown cannot be compared to the values in the table.
Why are ultraviolet lights used in chromatography?
Because most components are colourless, but they will fluoresce under UV light.
What is ninhydrin used for?
to make the components fluoresce under UV light.
why are paper and thin layer chromatography only used as guides to what is present?
Many other components may have that Rf value.
List 2 advantages for paper chromatography
cheap
little prep
more efficient for polar and water soluble compounds
easy to handle and store
List 2 advantages for thin layer chromatography
detects smaller amounts
better separation of less polar compounds
corrosive materials may be used
a wide range of stationary phases (powders) are available.
Why is HPLC useful?
Very sensitive.
e.g. drugs in blood
How much smaller are the particles in HPLC that in regular column chromatography>
10-20 times smaller.
Why does HPLC have very small particles?
allows the components to adsorb and desorb to the solid phase easier.
This makes the components separate more completely.
Why does HPLC need high pressure?
The small particles put up a lot of resistance.
Which is the most sensitive form of chromatography?
gas
What is the main problem with gas chromatography?
you can only use substances that won’t break apart when vapourised.
What type of chromatography is used to detect drugs in urine?
gas
What two questions can HPLC and GC answer?
- what is present
2. how much is present.
