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

Instrumentation/Operation
Area (arbitrary units)
100,000
4
80,000
3
60,000
40,000
20,000
2
1
0
0 2 4 6 8 10
Peak height (arbitray units)
8000
6000
4000
2000
0
0 2 4 6 8 10
Injection time [s]
Figure 59
Linearity of peak area and peak height as
a function of injection time for different
solutes 33
1 = mesityl oxide, 2 = phenylglycine,
3 = mandelic acid, 4 = benzoic acid
4
2
3
1
Factor Cause/effect Solution
Temperature changes • Changes in viscosity •Thermostat capillary
and injection amount
Sample evaporation • Increasing sample •Cap vials and/or cool
autosampler
Instrumental limitations • System rise time •Increase injection time
significant proportion
of injection time
Sample carry-over • Extraneous injection •Use capillary with flat,
smooth injection end
•Remove polyimide from
end of capillary
•Dip capillary in buffer or
water after injection
Zero-injection caused • Extraneous injection •Cannot be eliminated but
by simply dipping the can be quantified
capillary in the sample
Sample adsorption • Distorted peak shape •Change buffer pH
to capillary walls
• Non-eluting sample •Increase buffer
concentration
• Use additive
Low signal-to-noise • Integration errors •Optimize integration
ratio
parameters
•Increase sample
concentration
•Use peak height
Sudden application • Heating, thermal •Ramp separation
of high voltage expansion of buffer, and voltage
expulsion of sample
Electrokinetic • Variations in sample •Use hydrodynamic
injection matrix injection
Table 20
Factors affecting peak area reproducibility
102