Quantitative Analysis of Trace Isotope Impurity in Pharmaceutical Material by Terahertz Laser Spectrometer

Effects of isotope impurity molecule at low content were studied using THz laser spectrometer with high frequency accuracy. D-mannitol crystal was grown controlled to form monoclinic β-form. The lowest absorption peak of such β-form D-mannitol is known to show a very narrow FWHM below 1 GHz. D-sorbitol was added in the range 0.05 to 10.0 % in the solvent before crystallization. Peak frequency shifts of absorption lines of D-mannitol at 10 K on the relation with sorbitol content were evaluated by THz laser spectrometer with high frequency accuracy. It was shown that low content quantitative analysis of isotope impurity was possible.