Quantitative analysis of α-CL-20 polymorphic impurity in ε-CL-20 using Dispersive Raman Spectroscopy

Abstract: α-CL-20 polymorphic impurity in e-CL-20 studies have been carried out using Dispersive Raman Spectroscopy. e-, β-, αand γ-CL-20 polymorphs were produced using crystallization methods with sample recovery from the solution being >90%, and chemical purity of about 99%. The polymorphs prepared were characterized using Dispersive Raman Spectroscopy over the Raman shift region of 100-3500 cm-1 using a 514 nm argon ion laser. The experimental studies were supported by ab initio computations performed at B3LYP level using a 6-31+G** basis set. The computed vibrational frequencies of the CL-20 conformers correspond to the e, β and α or γ-CL-20 polymorphs when compared with the observed frequencies. α-CL-20 shows a distinct feature at 280 cm-1 as compared with those of the e-CL-20 polymorph. Using Dispersive Raman Spectroscopy, a linear relationship was demonstrated for the absolute peak height and absolute peak area ratio of α-CL-20 versus the weight percent of α-CL-20. This method enables a detection limit of this polymorphic impurity down to 2 wt%.