title: Simultaneous19F-1H medium resolution NMR spectroscopy for online reaction monitoring.
abstract: Medium resolution nuclear magnetic resonance (MR-NMR) spectroscopy is currently a fast developing field, which has an enormous potential to become an important analytical tool for reaction monitoring, in hyphenated techniques, and for systematic investigations of complex mixtures. The recent developments of innovative MR-NMR spectrometers are therefore remarkable due to their possible applications in quality control, education, and process monitoring. MR-NMR spectroscopy can beneficially be applied for fast, non-invasive, and volume integrating analyses under rough environmental conditions. Within this study, a simple 1/16″ fluorinated ethylene propylene (FEP) tube with an ID of 0.04″ (1.02mm) was used as a flow cell in combination with a 5mm glass Dewar tube inserted into a benchtop MR-NMR spectrometer with a1H Larmor frequency of 43.32MHz and 40.68MHz for19F. For the first time, quasi-simultaneous proton and fluorine NMR spectra were recorded with a series of alternating19F and1H single scan spectra along the reaction time coordinate of a homogeneously catalysed esterification model reaction containing fluorinated compounds. The results were compared to quantitative NMR spectra from a hyphenated 500MHz online NMR instrument for validation. Automation of handling, pre-processing, and analysis of NMR data becomes increasingly important for process monitoring applications of online NMR spectroscopy and for its technical and practical acceptance. Thus, NMR spectra were automatically baseline corrected and phased using the minimum entropy method. Data analysis schemes were designed such that they are based on simple direct integration or first principle line fitting, with the aim that the analysis directly revealed molar concentrations from the spectra. Finally, the performance of 1/16″ FEP tube set-up with an ID of 1.02mm was characterised regarding the limit of detection (LOQ (1H)=0.335molL-1and LOQ (19F)=0.130molL-1for trifluoroethanol in D2O (single scan)) and maximum quantitative flow rates up to 0.3mLmin-1. Thus, a series of single scan19F and1H NMR spectra acquired with this simple set-up already presents a valuable basis for quantitative reaction monitoring.
authors.affiliation: BAM Federal Institute for Materials Research and Testing, Richard-Willstaetter-Straße 11, 12489 Berlin, Germany.
authors.forename: Nicolai
authors.initials: N
authors.lastname: Zientek
authors.affiliation: BAM Federal Institute for Materials Research and Testing, Richard-Willstaetter-Straße 11, 12489 Berlin, Germany; École Nationale Supérieure de Chimie de Lille, Avenue Mendeleiev CS 90108, 59652 Villeneuve D'ascq Cedex, France.
authors.forename: Clément
authors.initials: C
authors.lastname: Laurain
authors.affiliation: BAM Federal Institute for Materials Research and Testing, Richard-Willstaetter-Straße 11, 12489 Berlin, Germany.
authors.forename: Klas
authors.initials: K
authors.lastname: Meyer
authors.affiliation: Department of Chemical Engineering, Technische Universität Berlin, Straße des 17. Juni 136, MA 5-7, 10623 Berlin, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Kraume
authors.affiliation: Pro(2)NMR, Institute of Mechanical Process Engineering and Mechanics and Institute of Biological Interfaces, KIT, Adenauerring 20 b, 76131 Karlsruhe, Germany.
authors.forename: Gisela
authors.initials: G
authors.lastname: Guthausen
authors.affiliation: BAM Federal Institute for Materials Research and Testing, Richard-Willstaetter-Straße 11, 12489 Berlin, Germany. Electronic address: michael.maiwald@bam.de.
authors.forename: Michael
authors.initials: M
authors.lastname: Maiwald
keywords: (1)H; (19)F; Data processing; Medium-resolution NMR; NMR; Online NMR; Process analytical technology; Quantitative NMR; Reaction monitoring