Chromatography Flashcards
What is the purpose of the stationary phase
-as the solvent sweeps the components in the sample being analysed, over the stationary phase they undergo a continual process of adsorption (the compost attached onto the solid stationary phase) followed by desperation (the component is disavowed and is being carried by the liquid mobile phase)
How are components in chromatography separated
Process of deferential adsorption and desorption leads to the component travelling at different speeds and thus they seperate out
What does rate of movement depend on
How strongly it adsorbs onto the stationary phase (degree of affinity) and how readily it dissolves in the mobile phase (degree of solubility)
What is the stationary phase in TLC
Silica/alumina and the mobile phase is a suitable organic solvent
Why is a small spot of the sample solution placed on the origin line?
If the initial spot is large then the tailing effect may result in inaccurate estimate of the rf
Why is the value of Rf lower than 1
Mobile phase has zero affinity towards the stationary phase therefore it travels furtherest distance in a given time.
How are substances identified
Qualitative: identification of a substance using chromatography can usually be made by comparing its Rf values to the Rf value of a pure analyse of the substance obtained under the same conditon
What is the function of the stationary phase
- The surface of the components adsorb with different degrees of affinities in order to separate.
- Affinity depends on the strength of attraction of the analyses made with the stationary phase. Higher the Mr, stronger the dispersion forces and has higher affinity to the non polar stationary phase
Function of the mobile phase
It is the carrier of the components (with degrees of solubility) through the stationary phase during separation
Stationary phase of HPLC
Solid non polar hydrocarbon packed into a column. A range of solids (granules) is available, some with chemicals bonded to their surfaces to improve the separation
Which component is swept out by the solvent last
The least soluble component, higher affinity, highest Mr, strongest dispersion, highest non polar character, highest Rf
Advantage of smaller granules used in HPLC
Surface area of the stationary phase increases. smaller particles allows for more frequent adsorption and desorption giving much better separation.
Disadvantage of smaller granules in HPLC
smaller particles create a considerable resistance t the flow of the mobile phase and the solvent is pumped through under high pressure
Qualitative and quantitative analysis of HPLC
The position of the peak Rt identifies each component (qualitative analysis). The height of the peak or area of the peak proportional to concentration (quantitative analysis)
