Quantitative Online NMR Spectroscopy in a Nutshell

Abstract

Online NMR spectroscopy is an excellent tool to study complex reacting multicomponent mixtures and gain process insight and understanding. For online studies under process conditions, flow NMR probes can be used in a wide range of temperature and pressure. This paper compiles the most important aspects towards quantitative process NMR spectroscopy in complex multicomponent mixtures and provides examples. After NMR spectroscopy is introduced as an online method and for technical samples without sample preparation in deuterated solvents, influences of the residence time distribution, pre-magnetization, and cell design are discussed. NMR acquisition and processing parameters as well as data preparation methods are presented and the most practical data analysis strategies are introduced.

Online Monitoring of Polymerizations: Current Status

“…[43][44][45][46] Quantitative online NMR spectroscopy coupled with batch/semi-batch reactors was reviewed by Maiwald and coworkers. [47] Next to classical proton NMR spectroscopy,…”

“…[43][44][45][46] Quantitative online NMR spectroscopy coupled with batch/semi-batch reactors was reviewed by Maiwald and coworkers. [47] Next to classical proton NMR spectroscopy, 129 Xe NMR spectroscopy was also employed to monitor styrene polymerizations in miniemulsion. [48] Zakharov and coworkers introduced in situ CT MAS NMR spectroscopy under continuous flow conditions to monitor the dynamics of propene polymerization over a supported Ziegler catalyst.…”

Practical aspects of real-time reaction monitoring using multi-nuclear high resolution FlowNMR spectroscopy

“…19 In addition, due to the high degree of temperature control required for magnetic field stability in low field instruments, the reaction sample must be brought to the magnet temperature before passing through the spectrometer to avoid disrupting the magnetic field homogeneity. 19 Multi-nuclear spectra have become possible with modern low field instruments, and deconvolution techniques can be used to alleviate some of the constraints on spectral resolution, 20,23 but high field instruments are clearly much more useful for reaction and catalyst development due to higher spectral resolution, increased sensitivity, and the ability to study a wide range of nuclei and perform advanced measurements. A significant advance in high field reaction monitoring has been the recent development of integrated flow tubes that can be inserted into a standard spectrometer probe without having to use specialised flow probes such as those developed for HPLC-NMR 6,7 or microfluidic devices, [24][25][26][27][28][29] reducing costs and greatly facilitating use of the technique.…”

“…17,30 With all these benefits of performing on-line reaction monitoring by continuous-flow high resolution NMR spectroscopy, the presence of flow can have significant effects on the quality and quantification of the NMR signal, and it is important that these effects are considered if accurate data are to be generated. Although some basic principles of how NMR data acquisition is affected by moving samples have been known for some time, 6,7 and the use of low field NMR spectroscopy in process monitoring has been well covered in the recent literature, 10,20,21,31 we felt it necessary to reinvestigate the considerations required for real-time reaction monitoring using high field FlowNMR with contemporary instruments and software. Here we report a summary of the most important effects and parameters that need to be considered when using multi-nuclear high resolution FlowNMR for accurate reaction monitoring with the aim of analysing kinetics and elucidating reaction mechanisms in the research laboratory.…”

Online monitoring of a photocatalytic reaction by real-time high resolution FlowNMR spectroscopy

“…This has been spurred on by the recent commercialisation of a number of dedicated FlowNMR monitoring systems [25][26][27][28] accompanied by several reports detailing considerations for their use. 26,29,30 On-line FlowNMR techniques utilize an external reaction vessel, situated outside of the influence of the magnetic field, with the sample continuously pumped into the spectrometer through a dedicated NMR flow tube located within a standard NMR probe, before returning to the reaction vessel ( Fig. 1).…”