What are the differences between desalting and buffer exchange?

Desalting and buffer exchange are both separation processes carried out using size exclusion chromatography (SEC), also known as gel filtration chromatography. There are a few significant differences between the two processes. 

Desalting: 

• Involves removal of salts from a sample
• Is achieved by first equilibrating the chromatography column with water

Buffer Exchange: 

• Involves replacing one set of buffer salts with another
• Is accomplished by first equilibrating the column resin with the desired buffer for the sample

In both cases, the solution with which the column is pre-equilibrated replaces the buffer constituents that carry the sample into the column.