you can try to dissolve it in 30% DMSO (30% DMSO and 70% sterile Distilled water) or Tween-20 to a required concentration before filtration. Moreover, you can use only water but you will need to add small amount of sodium hydroxide to enhance solubility of the tryptophan..

Thank you sir.  You've always been there.

Now I am using your publication on this Rufus!