retention time related guard column

[irene_wu]

hi, guys:
thank you all for helping me to solve the problem about back pressure. now I have a question about the retention time:

the retention time for same solution on column directly and column with guard column are same. why?suppose there should be some differences due to the total column lenth .

welcome any explaination

[tom jupille]

Actually, it should be longer by the increase in column volume. If you have a small guard cartridge, the differnce may only be a couple of percent.