Dear Sumira,

I do not undertstand. Which kind of HPLC do you have? Buffer should be a dilute aqueous solution (max. 50 mM of salt or ~0,1% TFA). It cannot cause any problem with flow or pressure if your other solvent is acetonitrile or methanol.

Gy Gyémánt

Using a buffer with a C18 column should not usually cause any problems. Are you accidentally precipitating the buffer in your system? If you add buffer to a column which contains a high percentage of organic solvent (eg for storage) then the buffer can precipitate. You may need to flush your column first with an aqueous solution containing a low percentage of organic (say 10% MeOH) before adding the buffer component.

Always 'ultrafilte (0.22 um)r' your buffers, mobile phases, and samples before they are used.

Mobile phase and samples are filtered  with 0.45micrometer filtre. we use 70% acetonitrile and methanol 30%. 

Acetate and phosphate buffers are very common in HPLC and these buffer solutions usually do not cause any problems, unless wrong concentration, wrong pH and old buffer solution with precipitations. Most C 18 columns usually function well pH 3 to 9 range and buffer solution pH should be verified first, than filtered with Nylon 0.45 micro filters. Buffer concentration should be controlled between 10 mM -50 mM, and after analysis flush system to remove buffer out from HPLC lines and store column in organic solvent like Acetonitrile or Methanol.