# 3,4-Methylenedioxyamphetamine (MDA) basic extraction

At my lab we perform a basic extraction of seized MDA with $\ce{NaOH}$ $\pu{2M}$ prior to GC/MS analysis. $\ce{MDA + NaOH -> MDA- + Na+ + H2O}$. This reaction should favor the products since $\mathrm{p}K_\mathrm{a}$ of MDA is about 10 and $\mathrm{p}K_\mathrm{a}$ of $\ce{H2O}$ is about 16. All of the MDA should be converted to its ionic form which is soluble in the aqueous layer. Why is there still enough of MDA in the organic layer ($\ce{CHCl3}$) to be detected by GC/MS?

MDA is an alkaloid, i.e., basic. When you talk about its $\mathrm{p}K_\mathrm{a}$ value, you're really talking about the $\mathrm{p}K_\mathrm{a}$ of the protonated ammonium ion.