Common faults and solutions of capillary electrophoresis

1.

1.

Possible cause: The capillary is blocked or broken

Solution: Rinse the capillary with water and observe if there is water flowing out

2.

Possible cause: bubbles are generated in the buffer or the sample is precipitated in the zone

Solution: Degas the buffer ultrasonically.

3.

Possible cause: The sample injection volume is too large

Solution: Reduce the injection volume

4.

Possible cause: The sample concentration is too low

Solution: Use a high-concentration sample to test.

5.

Possible cause: The detection wavelength is set incorrectly

Solution: Confirm the characteristic absorption of the analyte and check the detection wavelength setting

6.
Inspection result: the current is normal
.

Possible cause: Wrong separation polarity
.

Solution: For protein samples, pay attention to the PI and charge of the protein under the separation conditions
.
For nucleic acid samples, they are negatively charged under normal conditions
.

7.
Inspection result: the current is normal
.

Possible cause: The sample is adsorbed on the inner wall of the capillary
.

Solution: For protein and nucleic acid samples, try to use coated capillaries, extreme pH conditions or dynamic coatings to prevent sample adsorption
.

8.
Inspection result: the current is normal
.

Possible cause: The optical detector or optical fiber is damaged
.

Solution: Perform a standard sample test.
If there is no corresponding result, there may be a hardware problem
.

Two, electrophoresis peak tailing

1.
Possible cause: The capillary window is not open or the window position is not correct
.

Solution: Open the capillary detection window or adjust the position of the window
.

2.
Possible cause: The sample is adsorbed on the inner wall of the capillary
.

Solution: For protein and nucleic acid samples, try to use coated capillaries, extreme pH conditions or dynamic coatings to prevent sample adsorption
.

Third, the electrophoresis peak is asymmetry

1.
Possible cause: The incision of the capillary inlet is not flat
.

Solution: Re-cut the capillary inlet
.

2.
Possible cause: The electrolysis rate of the buffer solution and the sample solution is too different
.

Solution: Use buffer as sample solvent
.

Fourth, the electrophoresis peak is too wide

1.
Inspection results: reduce the sample injection volume and improve
.

Possible cause: The sample concentration is too high
.

Solution: Reduce the sample concentration or reduce the injection volume
.

2.
Inspection results: reduce the sample injection volume, no improvement
.

Possible reason: the sample itself is not uniform in nature
.

Solution: This reason is mainly for protein samples, and the probability of occurrence of small molecule samples is low
.

5.
Unstable migration time

1.
Inspection result: the peak time is unstable and irregular
.

Possible cause: The buffer solution balances slowly with the inner wall of the capillary
.

Solution: Avoid flushing the capillary with NaOH between each sample run
.

2.
Inspection result: the peak time is delayed in turn
.

Possible cause: The substance in the sample is easily adsorbed on the inner wall of the capillary
.

Solution: First, rinse the capillary with 0.
1N NaOH solution for a short time before each sample run, and observe whether the migration time can be repeated
.
If the effect is not good, use a coated capillary or process the sample again
.

6.
Unstable peak shape and peak time

1.
Check result: Change the type of buffer, the peak shape and peak time are stable
.

Possible reasons: the buffer is unstable, easy to electrolyze, or the sample is unstable under the original buffer condition
.

Solution: Replace other types of buffers
.

2.
Inspection result: changing the type of buffer, the peak shape and peak time are still unstable
.

Possible cause: The substance in the sample is easily adsorbed on the inner wall of the capillary
.

Solution: Use a coated capillary or pre-treat the sample
.

Seven, current leakage

1.
Inspection result: the capillary tube is broken
.

Possible cause: The buffer in the capillary flows out, causing current leakage
.

Solution: Replace the capillary, and clean the optical fiber head and detection window with water
.

2.
Inspection result: the capillary tube is not broken
.

Possible cause: The humidity in the experimental environment is too high
.

Solution: Use a dehumidifier or air conditioner
.
When the humidity is too high, the desiccant can be placed when the instrument is turned off, but the desiccant must be taken out when the instrument is running
.

8.
Cannot add air pressure

1.
Check result: the problem is solved after replacement
.

Possible cause: There is liquid at the neck of the bottle, which makes the stopper slippery
.

Solution: When filling the bottle with liquid, do not overfill or wet the bottleneck
.

2.
Inspection result: If the bottle stopper has no problem, the vacuum method can be used first, if the vacuum method can be used, but the pressure is still unavailable
.

Possible cause: There is a problem with the pressure system
.

Solution: overhaul
.

Nine, the migration time can be repeated, but the peak area repeatability is not good

1.
Inspection result: Re-cut the capillary inlet and the problem is solved
.

Possible cause: The capillary inlet incision is not flat
.

Solution: Re-cut the capillary inlet
.

2.
Inspection result: Re-cut the capillary inlet, the problem still exists
.

Possible cause: If the electric sampling can maintain reproducibility, there is a problem with the pressure control or the gas circuit
.

Solution: overhaul
.

10.
The capillary or electrode is easy to break

1.
Possible cause: the bottle cap is aging
.

Solution: Replace the cap
.

2.
Possible cause: The electrode is not vertical
.

Solution: Straighten the electrode
.

11.
Coolant leakage

1.
Possible cause: The gasket and the clip in the cartridge are missing or installed in the wrong order
.

Solution: Install in strict accordance with the installation order
.

2.
Possible cause: The internal pipeline of the instrument is not tightly sealed
.

Solution: overhaul
.