Bio-Rad Criterion™ Cell - Manual (Page 9)

Problem Cause Solution
2. Vertical streaking of protein. a. Sample overload. a. Dilute sample, selectively
remove predominant protein
in the sample, or reduce
voltage by about 25% to
minimize streaking.
b. Sample precipitation. b. Centrifuge sample before
addition of SDS sample
buffers, or decrease % T of
resolving gel.*
c. The ratio of SDS to protein
should be enough to coat
each protein molecule with
SDS, generally 1.4:1. It may
require more SDS for some
membrane protein samples.
3. Lateral band spreading. a. Diffusion out of the wells a. Minimize the time between
prior to turning on the sample application and
current power start up.
b. Ionic strength of sample b. Use some buffer in sample as
lower than that of gel. in gel or stacking gel.
4. Skewed or distorted bands. a. Salts in sample. a. Remove salts by dialysis,
desalting column, etc.
5. Lanes constricted at bottom a. Ionic strength of sample a. Desalt sample and neighboring
of gel. higher than that of samples.
surrounding gel.
6. Run taking unusually long a. Running buffer too a. Check buffer protocol, dilute
time. concentrated. if necessary.
b. Excessive salt in sample. b. Desalt sample.
7. Run too fast, poor resolution. a. Running or reservoir a. Check buffer protocol,
buffer too dilute. concentrate if necessary.
b. Voltage too high. b. Decrease voltage by
25-50%.
8. Doublets observed where a. A portion of the protein a. Prepare fresh sample buffer
a single protein species may have been solutions if over 30 days old;
is expected (SDS-PAGE) reoxidized during the run or increase 2-mercaptoethanol
may not have been fully concentration in the sample
reduced prior to run. buffer.
9. Observe fewer bands than a. Protein(s) migrating at the a. Increase % T of resolving
expected and one heavy dye front. gel.*
band at dye front.
b. Protein degradation. b. Use protease inhibitors, e.g.
PMSF, etc.
10. Diffuse Bands, poor resolution, a. Overheating a. Fill Criterion Cell tank to proper
irregular band pattern, inexplicable level.
artifacts.
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