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308309
CAPILLARY ELECTROPHORESIS
Description
undergraduate degree analytical chemistry Mind Map on CAPILLARY ELECTROPHORESIS, created by chaz_id89 on 28/10/2013.
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analytical chemistry
undergraduate degree
Mind Map by
chaz_id89
, updated more than 1 year ago
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chaz_id89
almost 11 years ago
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Resource summary
CAPILLARY ELECTROPHORESIS
ELECTROPHORESIS: HOW DOES IT WORK?
differential migration of charged sp. in applied DC
rate depends on CHARGED:SIZE RATIO
migration rate ν= μeE
Annotations:
μe = electrophoretic mobility α = ionic charge 1/α = frictional factors (size & shape, viscosity) E = applied field strength
electric field strength related to magnitude and length over which
migration rate : ν= μe x V/L
Annotations:
V: voltage L: length of slab/capillary
Plate #: N= μeV/2D
Annotations:
D: diffusion coefficient of solute
RESISTANCE (joule heating)
V = I x R
Annotations:
I = current R = resistance
if use gel - produce heat. limit V applied for slab elect. ~500v
Capillary typically 10-100μm ID and 30-100cm long (large surface:volume ratio = better cooling)
P = I^2/R
Annotations:
P = power dissipation = amt heat produced long capillary and small cross sectional area = high R
voltages we can use in cap.ele. typical applied voltage 10-25kV = E of 100-400 Vcm-1 typical N = 100,000 –200,000(HPLC 5,000 –20,000)
ELECTROOSMOTIC FLOW
high V applied - buffer-filled-Si cap. - bulk liq twds CATHODE
pressure-induced
electroosmotic flow
EO Flow generally > electrophoretic migratn
buffer = mob. phase
EO flow = mob. phase pump
all analytes are swept through column regarding the charged (CATION - NEUTRAL - ANION)
electroosmotic flow velocity ν= μeoE
Annotations:
μeo= electroosmotic mobility
ion velocityν= (μe+ μeo)E
migration rate tm= l/ (μe+ μeo)E = IL(μe+ μeo)V
Annotations:
L= Length of capillary l = length to detector
N = 16(tm/W)^2
CE HARDWARE
Small vol- cap (4-5μL), injector/detector < 10nL (the result not concentrated)
Cap: fused silica, external coating of polyimide (flexibility & durability)
can reverse the polarity: anions elute first
Sample Injection
5 -50 nL
tips that can sample directly from cell/cell substructure
Can be automated
electrokinetic
Annotations:
Voltage--> sample flow with EO flow + ion movement Injects larger amts of more mobile ions
pressure
Detectors (= HPLC)
Optical
Problem with low volumes = short pathlength = low absorbance or fluorescence
modify cell to increase the pathlength
Z-cell
Annotations:
- path length 10 x the cap. diameter - increase path length -> decreases in peak efficiency = add spherical ball lenses btwn source-zcell-detector. - Increase sensitivity
Bubble cell
Annotations:
bubble formed near the end of the capillary
Multireflection cell
Annotations:
a reflective coating of silver is deposited on the end of the capillary
Adsorption & fluoro. (limits in conc terms, but equal or better in mass detection limits)
Indirect detection
for compounds that don't have suitable chromophore/molar absorptivity - add ionic chromophore in the buffer, see any reduction in that signal
Electrochemical
conductivity & amperometry
MS
small volume of flow rate (1uL/min) allow to couple w MS
common use of electrospray Ionisation (ESI)
use volatile buffer
CE/MS - use to detect proteins, DNA fragments n peptides. (large biomolecules)
APPLICATIONS OF CE
Capillary Zone Electrophoresis
small ions
cation separations- wall untreated, analytes flow with EO flow twrds cathode
Anions separation- wall treated, reversed EO flow twrds anode
molecular sp.
ions or non-ion (derivatization) - herbicides, persticides, proteins, aa. etc
- buffer composition is constant - ionic components migrate into zones (complete resolved zone have buffer between zones)
Capillary Gel Electrophoresis
performed in porous gel polymer matrix w a buffer mixture that fills the pores of the gel
types of gel : polyacrylamide polymer, agarose, methyl cellulose etc.
Capillary Isoelectric Focusing
separate amphiprotic sp. (aa, proteins - have weak COOH and AMINE gp.)
Annotations:
amphiprotic - sp in a soln is capable to donate or accept a proton.
buffer mixture that continuously varies in pH along its length
Media attachments
pressure-induced (image/png)
electroosmotic_flow (image/png)
cap.electrophoresis (image/png)
Z-cell (image/png)
bubble_cell (image/png)
multireflection_cell (image/png)
APPLICATIONS_OF_CE (image/png)
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