1. Disconnect the column and reconnect it to the chromatograph with the flow through the column in the reversed direction.
2. Flush out any salts/buffers with HPLC grade water. Pump 25 mL of water through the column at 1 mL/min.
3. Flush column with 25 mL of isopropanol.
4. Flush column with 25 mL of methylene chloride.
5. Flush column with 25 mL of hexane.
6. Flush column again with 25 mL of methylene chloride.
7. Flush column again with 25 mL of isopropanol.
8. Reconnect the column to the chromatograph with the now in the proper direction. Flush the column with the mobile phase without the buffer, then re-introduce the buffer.
9. Equilibrate the column with 25 to 50 mL of mobile phase.
10. Inject a standard or a sample to see if performance is restored.

Note:
For some retained compounds that have fouled the column, dimethyl-formamide may be a better "cleaning" solvent than methylene chloride and hexane.

1. Connect the column to the chromatograph with the flow in the reversed direction.
2. Flush column with 50 mL of 50:50 methanol:chloroform.
3. Flush column with 50 mL of ethyl acecate.
4. Reconnect the column in the proper flow direction.
5. Equilibrate the column with 50 mL of mobile phase.
6. Inject a standard or a sample and evaluate performance.

Caution
In general, it is worth trying to clean and back flush an HPLC column with appropriate solvents before trying to replace the frit. There is always a danger that small amounts of packing material may be lost when a frit is replaced and column efficiency will decrease. In addition, the use of an 0.5 µm in-line filter to capture particulate material and routine column washes with an appropriate strong solvent are highly recommended.