[Golden_4_Life]

If the solvent bottle says "passed thru a 0.25 micron filter", then why is it necessary for me to have to filter thru a 0.5 micron filter?  Pls correct me if I am mis-stating this, but does it not render it unnecessary then to have to re-filter thru a filter that is of a wider bore than what the solvent was manufactured?

[doc30]

You never know if contamination can get into your HPLC. Columns are expensive so it's always a good idea to keep your solvents as clean as possible.

[Golden_4_Life]

Thanky DOC---yet, I shall continue to filter notwithstanding the irrelevancy of it in this particular case.

[JGK]

The solvent may well have been filtered during its manufacture but you cannot rule out the possible entry of inert particulate matter during:

The bottling process;
Once the container's seal has been broken for the first time;
During mobile phase preparation.

Filtration following preparation eliminates these possibilities.