Load the elution fraction containing the target protein into the filter and centrifuge at 14,000 x g for ~10-30 minutes or until the volume has decreased. Repeat this until the total elution volume has decreased ≤ 25 µL for LC-MS or ≤ 80 µL for I2MS. If the buffer is already acidic (TFA or FA), no additional buffer exchange is required. However, if the elution buffer is not acidic (ex: 100 mM Tris Base), buffer exchange should be performed.