If my memory serves me then kratom's main alkaloids all can basically be extracted using the method as said above, do a NaOH extraction but i would recommend instead of naptha pure ethanol or if you have it chloroform. They are easier/better in for the process.. though note the risks of using chloroform, while it is a good solvent for the freebased alkaloids it is still chloform
.. keep safe... hope iv been of help..
Panda