Effects of Low Content Enantiomer Impurity in L-histidine Crystal Observed by Terahertz Spectroscopy

Effects of enantiomer impurity molecule at low content on terahertz spectrum were studied. L-histidine crystal was grown controlled to monoclinic form B from ethanol-rich solvent. D-histidine was added in the range 0.05 to 10.0 % in the L-histidine aqueous solution before recrystallization. Peak frequency shifts of absorption lines of L-histidine at 10 K on the relation with D-histidine content were evaluated by high frequency accurate terahertz spectrometer. It was shown that high sensitive detection of enantiomer impurity was possible until DL racemic compound crystal was formed with increasing D-histidine content.