Here is some info about the pistons: Red: Worked in every case but organics and hi temp. Teflon w/glass fill - so it is a much more abrasive seal. However, seals well - and is a good default seal Tan : Created for high temperature applications, originally for GPC - not good as an overall seal. Black: ITB SEAL - Graphite filled Teflon. Not great for aqueous mobile phases and buffers. Causes shedding. In the correct applications, it lasts longer and is less abrasive. Clear : OPTI-SEAL - UHMW-PE preforms best with aqueous solutions w/buffers. Excellent seal but not as forgiving."allow to stand for 30 minutes. Separate CHCl3 layer and evaporate solvent almost to dryness. Add 0.1 ml Et2O or acetone for GC analysis.