Higuchi et. al, "Direct Potentiometric and Titrimetric Determination of Methadone in Urine with Plastic Electrodes Selective for Hydrophobic Cations,", 1978, Box: 10, Folder: 95. Personal papers of Takeru Higuchi, PP 359. University of Kansas. Kenneth Spencer Research Library. https://archives.lib.ku.edu/repositories/3/archival_objects/124519 Accessed June 01, 2024.