Crystallise the monohydrochloride from aqueous EtOH or 60% aqueous EtOH (m 259odec). Alternatively dissolve 10g in 50mL of H2O, decolourise with Norite, filter, evaporate it in a vacuum to a syrup, cool to room temperature, add 95% EtOH with stirring until slightly turbid, scratch the sides of the vessel until crystals form, then add slowly 40mL of EtOH and keep at 0o overnight, filter the solid off, wash it several times with EtOH and dry it in a vacuum. [Cox J Biol Chem 78 475 1929, Cox et al. J Biol Chem 81 73 1929, Greenstein & Winitz The Chemistry of the Amino Acids J. Wiley, Vol 3 pp 1972, 2098 1961, Beilstein 25 II 407, 25 III/IV 4346.]
