Preliminary study of experimental parameters for projection moving-window two-dimensional correlation FTIR spectroscopy

Abstract

Our group proposed the projection moving-window two-dimensional (Proj-MW2D) correlation FTIR spectroscopy in 2015. In this study, the influence of three important experimental parameters on the quality and accuracy of Proj-MW2D was investigated, including the number of scans, the spectral resolution, and the heating rate. By changing parameters, a total of 36 in situ FTIR experiments of isotactic polypropylene (iPP) upon heating from 30 °C to 210 °C were performed. Proj-MW2D and conventional MW2D FTIR spectra were then calculated. It was confirmed that the quality and accuracy of Proj-MW2D were actually predominated by the number of spectra collected (codetermined by above three parameters). Importantly, a big problem of Proj-MW2D spectroscopy was found that the number of spectra used to calculate Proj-MW2D spectra cannot be too few, otherwise the results will lead to an error. It was also confirmed that the heating rate itself has a negative impact on Proj-MW2D in the temperature axis when a very fast rate was used (15 °C/min). This study summarized the optimal experimental parameters: 1) 2−4 cm−1 (the spectral resolution); 2) 10–30 scans (the number of scans); 3) 2–10 °C/min (the heating rate). Moreover, please ensure the number of spectra is ≥ 72 at least. More accurately, when using a linear heating, there should contain 0.4 spectrum per 1 °C at least. These findings are also applicable to other types of two-dimensional (2D) correlation FTIR spectroscopy based on the moving-window. People can follow the recommendations to avoid unnecessary mistakes.