In a 2008 book on analytical chemistry, an author describes converting iso-LSD into LSD using a simple method involving warm ethanolic sodium hydroxide. Although the author describes it as extremely efficient, Erowid is interested to know whether this method has been used by either law enforcement or underground chemists to purify/enhance LSD.

"This method also included an additional step to convert iso-LSD, a common contaminant of illicit LSD, into LSD using ethanolic sodium hydroxide and heat (50ºC for 10 min). This process converted iso-LSD into LSD with approximately 98% efficiency, thus effectively combining both of the compounds into one single peak. This allowed assessment of the total amount of LSD, in either isomeric form, in the sample since neither of these drugs is naturally occurring nor have any legitimate source. Although at its surface a reasonable procedure, it has not been adopted by the forensic community."
--Cody JT. "Hallucinogens". Chapter 4. p 175-201 in Bogusz MJ (ed.). Forensic Science: Handbook of Analytical Separations, Vol 6. Elsevier. 2008.

Note that sodium hydroxide has low solubility (<13.9 g/100 mL) in ethanol.