I once read somewhere that proper LSD purification consists of fractional crystallisation and/or chromatography to separate the LSD from the inactive iso-LSD,  followed by isomerising the iso-LSD in methanolic KOH to an equilibrium mixture of LSD and iso. The separation process is repeated in order to improve yields for the overall procees, but an some point it becomes a case of diminishing returns. In light of all this, the quality of an LSD experience, as far as I understand, comes down to the degree of care that the manufacturer puts into this separation process (since it will also clean up any other impurities left over from the synthesis).

I can't promise you much in the way of reading materials right now, but if something comes up I'll try and remember to put it here.