Homo- and Hetero-Covariance NMR Spectroscopy and Applications to Process Analytical Technology

Abstract

Covariance processing of data and spectra has established itself among the computerbased NMR spectroscopy methodologies to increase sensitivity and resolution and to facilitate spectral analysis. While homo-correlations yield two-dimensional (2D) diagonally symmetric or antisymmetric spectra, hetero-covariance transformations allow to transfer NMR chemical shift information to other spectroscopic techniques, such as near infra-red or Raman. This is visualized as a 2D correlation map, provided a common indirect or perturbation domain, such as time, concentration change, and pressure. Covariance spectra can be generated as synchronous or asynchronous maps. The synchronous map relates the signals of species, e.g., educts and products. The asynchronous spectrum allows to derive the sequential order in which such species occur relative to each other. After a theoretical introduction into covariance NMR, its application in process analytical technology is discussed for wine fermentation, a radical polymerization reaction, a continuous process ethanol production using immobilized yeast, and a Knoevenagel condensation in a microreaction system. The covariance approach is extended toward two perturbation variables and quantitative relationships through PARAFAC kernel analysis and is illustrated for the preparation of polylactic acid nanocomposites. The advantages and added values of using synchronous and asynchronous spectra to gain process knowledge and control are demonstrated.

Using Compact 1H NMR, NIR, and Raman Spectroscopy Combined with Multivariate Data Analysis to Monitor a Biocatalyzed Reaction in a Microreaction System

“…Since the uniqueness of the solution is determined by the secondary conditions, such as the chemical model, reaction order, and pure educt or product spectra, it is important to introduce as much physical-chemical knowledge of the system as possible into the constraints [34,38] [16,18]. is perturbation may be temperature, pressure, concentration, stress, electrical field, and most importantly a chemical reaction [17,41]. A correlation spectrum or map, X(] 1 , ] 2 ), is defined according to the following equation:…”

“…Due to the statistical nature of the approach, one series of spectra may be compared to another series of spectra originating from a different spectroscopic technique. is is referred to as heterocovariance spectroscopy [21,41]. A heterocorrelation map will result according to the following equation:…”

Application of green analytical chemistry to a green chemistry process: Magnetic resonance and Raman spectroscopic process monitoring of continuous ethanolic fermentation

“…Automated analyses should be performed preferably without sample preparation and in real time (Maiwald et al, ; Meyer et al, ; Rathore, Bhushan, & Hadpe, ; Rosas, Blanco, González, & Alcalà, ; Singh et al, ; Sugimoto, Fukuyama, Sumino, Takagi, & Ryu, ). Through an equally automated data analysis, the raw data may be received, centrally stored and converted into meaningful and applicable plots or diagrams such as concentration–time ( c–t ) diagrams (Jaeger & Legner, ; Wu, Li, & Gao, ). These diagrams represent the regular or optimum course of the process and might be accompanied by a confidence band.…”