High performance capillary electrophoresis - T.E.A.M.

4.2.4 Migration time/mobility reproducibility
Run-to-run migration time and mobility reproducibility in CE
can often be better than 0.5 % RSD. This value is dependent
on the condition of capillary wall, the composition, pH, and
viscosity of the buffer, and the nature of the sample, and
quality of instrumentation. Additional detail is given in table
17.
Factor Causeleffect Solution
Temperature • Changes viscosity • Thermostat capillary
change
and EOF
Adsorption to • Changes EOF • Condition capillary
capillary walls • Caused by buffer, additive, and allow sufficient
or sample adsorption equilibration time
Hysteresis of • Caused by conditioning • Avoid pH differences
wall charge
capillary at high (or low)
pH and employing a low • Allow sufficient
(or high) pH running buffer equilibration time
Changes in buffe • pH changes due to • Replenish buffer
composition
electrolysis
• Buffer evaporation
• Cap buffer vials and
cool carousel
• Conditioning waste
• Use separate reservoir
flushed into outlet
to collect wash solutions
reservoir
• Carrying sodium hydroxide • First dip capillary in
from conditioning vial into separate buffer or
buffer vial, for example water vial
Buffer reservoirs • Non-reproducible • Level liquid in reservoirs
not level laminar flow • If not replenishing, do
not use inlet vial for
washing capillary
Different silanol • Different wall charge • Measure EOF and
content of silica and variations in EOF normalize if necessary
batches
Instrumentation/Operation
Table 17
Factors affecting migration time
reproducibility
Variations in • Proportional changes • Not user accessible
applied voltage in migration time
95