3.16- Chromotography Flashcards
What is chromotogoraphy
Chromotography is an analytical technique that seperates components in a mixture between a mobile phase and a staionary phase
What different states could there be in a monile phase and a stationary phase
The mobile phase may be a liquid or a gasin GC , the staionary phase may be a solid like in TLC or a liquid on a solid support like in GC
How do the 3 main types of chromorography work
.TLC, thin layer chromotography, a plate is coated with a solid and a solvent moves up the plate
. Columm chromotography, a column is packed with a solid and a solven moves down the column
.Gas chromotography, a column is packed with a solid or with a solid coated by a liquid, and then a gas is passed through the columb under pressure at high temperatures
What is the formula for Rf
Rf value = Distance moved by amino acid/ Distance moved by the solvent
Go into depth about how thin layer chromotography is carried out
. Wearing gloves, pencil line drawn 1 cm above the bottom of a TLC plate and mark spots for each sample equally spaced along the line
. Use a capillary tube to add a tiny drop of each solution to a different spot and allow the plate to air dry
. Add solvent to a chamber or a large beaker with a lid so that is no more than 1cm in depth
.Place the TLC plate into the chamber, make sure that the level of the solvent is below pencil line
.When the level of the solvent reaches about 1 cm from the top of the plate, remove the plate and mark the solvent level with a pencil, then allow the plate to dry in the fume cupboard
. Place the plate under a UV lamp in order to see the spots
.Calculate the rf values
Why are the different method and appatus used in TLC
pencil line- will not dissolve the solvent
tiny drop- too big a drop will cause different spots to merge
depth of solvent- if the solven is too deep it will dissolve the sample spots from plate
lid- to prevet the evaporation of toxic solvent
UV lamp- used if the spots are colourless and not visible
What is two directional chromotography
In order to seperate a comple mixture that has components of different solubility in solvents, it may be necessary to do chromotography with 2 different solvents
A spot of the mixture on a TLC plate is first seperated with one solvent and then the plate is rotated 90 deg and the plate is placed in a second solvent for a second seperation to take place
How is column chromotography carried out
. A glass tube is filled with the stationary phase usually silica/alumina in powder form to increase the surface area
. A filter or plug is used to retain the solid in the tube, solvent is added to cover all of the powder
.The mixture to be analysed is dissolved in a minimum of a solvent and added to the column
. A solvent or mixture of solvents is then run through the column
. The time for each component in the mixture to reach the end of the column is recorded
. What is HPLC, stands for high performance liquid chromotography and it is commonly used in industry
.HPLC- stationary phase is a solid silica
. HPLC- mobile phase a liquid
How is gas liquid chromotography carried out
.Gas liquid chromotography can be used to seperate mixtures of volatile liquids
. The time taken for a particular compound to travel from the injecrtion of the sample to where it leaves the column to the detector is known as its retention time, this can be used to identify the substance
. Some compounds have similar retention times so will not be distinguished
Why are inert carrier gas used
Gasses like helium or nitrogen are intert, these will not react with the componenbts being seperated in the GC column
What factors of gas chromotography can be used to change the retention times
The GC column temperature, column length, flow rate if the temperature or the flow rate is higher then substances will more quickly throught the column to give shorter retention times
How is GC-MS used
It is used in analysis, in forensics, enviromental analysis, airport security and space probes,
What is GC-MS
It is a mass spectrometer combined with GC to generate a mass spectra which can be analysed or compared with a spectral database by computer for positive identification of each component in the mixture
