Separations
Laboratory Separations &
Extractions

Types of Filtration




Methods of Separation





Gravity Filtration
Suction Filtration
Sinter Funnels
Centrifuges
Separating Funnels
Distillation
Rotary Evaporation
Extraction Methods



Extracting Solutes from Liquids
Solid Phase Extraction
Soxhlet Extraction
Why Separate?

To separate solids from liquids



Liquids from other liquids



Removing accelerants from a fire scene from the water used
to put the fire out!
Extract solutes from solvents


Panning for gold!
Removing precipitates (ppts)
Removing drugs of abuse from blood
Soluble components from insoluble components
Methods differ dependent on the phases of the
substances involved and the amount of material
present
Gravity Filtration






Separates solids from liquids
Used when the liquid is
retained
Filter paper is folded and
placed inside the funnel
A conical flask is placed
underneath to catch the
filtrate
Filter paper is fluted or a cone
Fluting gives greater surface
area, so filtering is quicker
Suction Filtration









Used when the solid precipitate is
needed
A round filter paper is placed inside a
Buchner funnel
The side of the Buchner flask is
attached to a vacuum
Buchner flask should be clamped
Prevents toppling
Do not allow filtrate to reach the
suction arm
Fine ppt can block pores and make
the process slower
Let the ppt settle before turning on
the suction
Hirsch funnel can be used for small
quantities
Buchner
Funnel
Buchner
Flask
Hirsch
Funnel
Sinter Funnel





Used for gravimetric
analysis
For small amounts of
solids
Sinter funnel weighed
before and after filtration
Sample + funnel dried to
a “constant weight”
The amount of
substance can then be
determined
Centrifuges








Solid can be removed from a
small amount of liquid
E.g. blood cells from blood
plasma
Sample placed in a vial
Vial is then placed in a rotor
Balancing the rotor is very
important
Vials are put opposite each other
on the rotor
Rotors spins at varying
thousands of rpm (revolutions
per minute)
The solid is forced into the base
of the vial
Separating Funnels






For immiscible liquids (i.e.
liquids that don’t mix)
E.g. diethyl ether and water
The mixture is poured into the
funnel
The layers are allowed to
separate
The lower layer can then be
tapped off
REMEMBER – remove the
stopper when tapping off the
bottom layer, otherwise a
vacuum will be formed!
stopper
separating funnel
lower layer
(more dense)
upper layer
(less dense)
tap
Distillation








For separating miscible liquids
Boiling points must be different
by 10˚C
Mixture is heated in roundbottomed flask
All joints should be greased to
ensure a good seal
First liquid reaches boiling point
Vapours travel up to the Liebig
condenser, which is water cooled
Vapours condense (distillate)
Distillate is collected in a
receiving flask
Rotary Evaporation







For removal of large amounts
of low boiling solvent
Sample is contained in a
large round-bottomed flask
Which rotates gently in a
heated water bath
Vacuum pump reduces the
pressure – which makes
solvent boils at a lower temp
than normal b.p.
Solvent vapours are cooled in
a water cooled condenser
Solute is left in the round
bottomed flask
Condensate collected in the
receiving flask.
Extraction of Solutes from Liquids





Separating funnels can be used
Move the solute from one solvent to another immiscible solvent.
Solvent containing solvent and extracting solvent are put in
separating funnel
Stopper the funnel and shake
Release the pressure







Hold the funnel upside down
Make sure funnel is held in
Open the tap
Repeat several times
Allow to settle (right side up)
Remove stopper
Tap lower liquid
Common Uses



Extraction of organic compounds from water into an organic
solvent
E.g. extracting pesticides from drinking water into organic solvent
for analysis
If upper layer is water





The extracting solvent is less dense
Run off the lower layer
Add more solvent
Extract again and add to original sample collected
If lower layer is water




Run off the water
Collect the solvent in a collection vessel
Replace the water back into the separating funnel
Repeat extraction
Solid Phase Extraction (SPE)









More sophisticated than the separating
funnel method
Very large sample size
Sucked through a a cartridge containing
an adsorbent
Organic compounds adsorb to the
adsorbent
The run off water is collected in a side-arm
flask
The flask is then emptied and a collection
tube placed inside it.
Another organic solvent (a few mil) is
passed through the sample
The solvent desorbs the sample from the
solid phase and is collected in the
collection tube
SPE extracts AND concentrates the
organic component
SPE cartridge
sorbent
suction
collection tube
side-arm flask
Soxhlet Extraction











For extracting soluble species from an
insoluble matrix
E.g. pesticides in soil or on the surfaces of
fruit and vegetables
The sample is held in a porous thimble
Solvent is held in a reservoir below
Solvent is heated
Solvent vapour rises up the tubing,
condenses and collects around the thimble
Soaking the thimble and the sample
The solvent then siphons back into the
reservoir
The solvent absorbs the sample from the
thimble and carries it to the reservoir
This process repeats and the extracted
sample congregates in the reservoir.
Then the rotary evaporator is used to
remove the excess solvent.