What dissolves cellulose but doesn't react with amines or esters?

[fastandbulbous]

Ion exchange resin isn't expensive. I couldn't comment on the ultrasound device though

 

[vecktor]

I think maybe you are taking the wrong approach, if you are using an alcohol for primary extraction it helps to use isopropanol or butanol and an acid. there are quite a few industrial alkaloid extractions from fibrous material, almost always they grind and use an acidified alcohol.

did you test the residue for alkaloids after extraction? you might also find that the alkaloid content of the material is pretty low and you are extracting all there is to get, especially if you are using some literature percentage content.