is CE a chromatography
no
what is CE
- separation of charged analyte in applied electric field.
- while chromatography is separation based on distribution of two phase on different rate
what is the challenge in CE
- joule heating: caused by the current flowing through the tube
what components that affect heat
heat is proportional to applied electric field and diameter of the tube
how does joule heating affect resolution
cause lost of resolution
what is the possible solution for joule heating
- narrowing tune: because heat is proportion to the tube diameter
-less conducting buffer solution: to reduce current flowing through the tube.
- cold temperature
how does capillary affects the separation
the short the capillary the first the separation
what is the commonly used capillary material
fused silica
what happens when pH of the buffer added is lower then the pKa of the silica
- this will cause silica surface / silanol group to be protonated or positively charged and we will have neutral capillary surface
what happens when pH of the buffer added is higher then the pKa of the silica
- this will cause silica surface / silanol group to be de-protonated means they will release proton and this will cause excess positively charged in the capillary surface and negatively charge surface.
what is the double layer of silica surface
i the formation of two layers
- immobilized layer: when proton bound to the negatively charged surface and do not mobile.
- diffuse layer: when ions are freely moving in the liquid near capillary wall.
what is EOF (electroosmotic flow )
- is the net liquid flow to ward the cathode or
- applied potential along the capillary by electrode at the end of the capillary.
what is the consequence of applied electrode
this will cause the excess cation to be attracted by the cathode.
what is flat flow profile
is the flow mostly created near the capillary wall.
why do we need to control EOF
because some application in the capillary require higher EOF and other requires lower EOF
so how can we regulate the EOF/ solution on how to control EOF
we can regulate it according to the
- capillary material. by choosing capillary material that produce lower EOF at higher pH.
EX: pyrex
- buffer pH: because pH increase with increase of the EOF
- electric field applied along the capillary: by increasing the voltage we speed up the EOF.
- temperature: by increasing the temperature you lower the viscosity which increase EOF
- surfantact: when we add surfactant that interact with the charged silanol group at the wall will be mask the charges and neutralize them means we lower charges at the capillary wall with lower the EOF.
how is the silica affected by the pH which will affect the EOF regulation
at acidic condition means lower pH silica surface is quite uncharged means less EOF but when the pH is increase the surface is deprotonated causing the increase of the EOF.
what does separation in CE based on
ions in CE are moved based on charges and size
what happens when EOF is greater than EP of anion
cation and anion can be analyzed together
what is effective mobility
is resulting mobility of combined of two forms (charged and uncharged)
by considering the formula of electrophoretic mobility how is it affected by charge, radius and viscosity
electrophoretic mobility increase with large charge of ion and decrease with increase of radius and viscosity.
