Principles of chromatography Flashcards
what is chromatography
the science of seperation
how do sample components partition
according to their relative affinity for the stationary or mobile phase
what are the components to be seperated
solute and analyte
what is the partition coefficient also known as
distribution co-efficient
define the partition coeffcient
ratio of concentrations in a mixture of two immiscible phases at equilibrium
equation for P
P=[organic]/[aqueous]
what does it mean if the P value is less than 1
hydrophillic
what does it mean if P is greater than 1
hydrophobic/lipophillic
why is P useful
when looking at reference tables it is easy to hydrophobic or phillic molecules
purposes of chromatography
analytical
preparative
what is meant by analytical
separate and identify compounds
determine the composition
what is meant by preparative
-fractionation
-isolate and purify compounds for collection from a mixture
How does seperation occur
analytes move through the mobile phase at different rates
describe the stationary phase in TLC
adsorbent matrix
what is TLC
thin layer chromatography
adsorbent vs absorbent
adsorbent means to stick to the outside
absorbent means to be taken in
materials used for the stationary phase of TLC
silica gel
alumina oxide
cellulose
what is used to identify or characterise analytes of interest compared to standards/references in TLC
Retention factor
describe column chromatography
a solid stationary phase is contained in a cylinderical tube. The sample is loaded into the cylinder. a liquid mobile phase is passed through the cylinder using gravity or high pressure. The sample is seperated according to relative affinity of the compounds to either the mobile or stationary phase
if compound A has lower affinity for the stationary phase than compound B which will elute first
Compound A
what is a chromatogram?
elution profile or detector signal plotted as a function of time
define retention time
time from when the sample is injected into the mobile phase to the apex of the eluting peak
define resolution
the difference in rentention times of two closely spaced peaks / distance between peaks divided by the average width of the peaks
define seperation
difference/distance between two close peaks
what R value indicates complete seperation
> 1.5
describe the resolution if there is overlap
no resolution
how can baseline resolution be acheived
increasing seperation or making the peaks more narrow
how to make peaks more narrow
increase column effciency
how to increase seperation
better column selectivity
what is the theoratical plate concept
mathematical concept used to describe the efficiency pf a chromtography system
-capacity/ability to seperate peaks
what is a theoratical plate
hypothetical zone used to conceptuliase the sections of the column at equilibrium for mass transfer between mobile nad stationary phases
how are theoratical plates calculated
according to peak width using an equation
how are analytes measured
using a detector
what does quantitative analysis do
quantify amount
what does qualitative analysis do
identify compounds
types of chromatography
HPLC
GS
SFC
