Abstract-MULTIVARIATE QUANTIFICATION OF MEBENDAZOLE POLYMORPHS BY TERAHERTZ TIME DOMAIN SPECTROSCOPY (THz-TDS)

Vitor Hugo Silva,   Francisco Senna Vieira,  Jarbas Jose Rodrigues Rohwedder ,   C Pasquini and  Claudete F. Pereira
   
http://pubs.rsc.org/en/Content/ArticleLanding/2017/AN/C6AN02540D#!divAbstract

This work presents an analytical method based on terahertz-time domain spectroscopy (THz-TDS) and partial least squares (PLS) regression models to quantify mebendazole (MBZ) polymorphs (forms A, B and C) in pharmaceutical raw materials. Mebendazole polymorphs A, B and C were quantified with RMSEP values of 1.5% w/w, 1.2% w/w and 1.8% w/w, respectively. The limits of detection (LOD) ranges obtained with the best PLS regression models were 2.7-4.3% w/w, 2.9-4.0% w/w and 2.4-3.1% w/w, for polymorphs A, B and C, respectively. This analytical performance is better than those for methods described in the literature using near (NIR) and middle (MIR) infrared spectroscopies. The main advantage of THz spectroscopy is its ability to access directly information related to crystal lattices. According to the results, the developed method is a powerful technique for quantification of MBZ polymorphs in raw material. This methodology can be implemented as a process analytical technology (PAT) tool for quality control of pharmaceutical feedstock.

Abstract-DETERMINATION OF CELLULOSE CRYSTALLINITY BY TERAHERTZ TIME DOMAIN SPECTROSCOPY

Francisco Senna Vieira and Celio Pasquini

http://pubs.acs.org/doi/abs/10.1021/ac4035746

Anal. Chem., Just Accepted Manuscript

DOI: 10.1021/ac4035746

Publication Date (Web): March 23, 2014

Copyright © 2014 American Chemical Society

Terahertz time domain spectroscopy (THz-TDS) has the ability to probe the crystallinity of several materials, due to the interaction of THz radiation with optical phonons in crystal lattices. In this work, THz-TDS has been used to quantify the degree of crystallinity of microcrystalline cellulose (MCC) samples. The THz spectra of cellulose present absorption features which could be directly correlated with the crystallinity index (CI) obtained by means of the well-established powder x-ray diffraction (PXRD) technique. The effect of THz time-domain signal processing was investigated and both univariate and multivariate, based on partial least squares (PLS), regressions were carried out with the signal in the frequency domain to correlate the THz spectra with CI. The results show that the multivariate regression models based on spectral data, collected with the sample displaced from the focal plane of the THz optics to improve representativeness and measurement repeatability, present the best performance with external validation achieving an absolute root mean square error of prediction (RMSEP) of 4 % for CI. This result compares well with the PXRD technique.