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Die quantitative NMR-Spektroskopie (qNMR) gewinnt in den letzten Jahren immer mehr an Bedeutung, speziell hinsichtlich der Anwendung auf komplexe Fragestellungen der analytischen Chemie. Ein großer Vorteil dieser Methode ist die Möglichkeit der Relativquantifizierung durch das „Zählen von Kernspins" in der Probe. Unter der Voraussetzung eines korrekt ausgeführten NMR-Experiments ist so der direkte Vergleich von Signalflächen im Spektrum möglich, ohne dass zuvor zwingend eine Kalibrierung notwendig ist.
Die NMR-Spektroskopie stellt heutzutage eine der wichtigsten Analysenmethoden in der organischen Chemie dar. Während der Großteil aller Untersuchungen qualitativ mit dem Ziel der Stoffidentifikation und Strukturaufklärung erfolgt, erlangt die quantitative NMR-Spektroskopie (qNMR) zunehmend an Bedeutung in Forschung und Industrie. Der entscheidende Vorteil gegenüber anderen Analysenmethoden liegt in der direkten Proportionalität der Signalfläche zur Anzahl Kernspins im Messvolumen. Dies erlaubt eine kalibrationsfreie Relativquantifizierung. Zur Absolutquantifizierung reicht die Zugabe einer definierten Menge eines vom Analyten unabhängigen NMR-Standards aus.
Trotz dieser Vorteile findet sich die qNMR bislang nur vereinzelt in Normen und Standardverfahren wieder. Zahlreiche Ringversuche in Metrologie und Industrie demonstrieren die Leistungsfähigkeit moderner NMR-Spektrometer und stärken das Vertrauen in die Methode. Die Entwicklung von Validierungskonzepten, sowie die kommerzielle Verfügbarkeit geeigneter zertifizierter Referenzmaterialien erleichtern die Anwendung, insbesondere im zumeist stark regulierten industriellen Umfeld.
Neben etablierten Hochfeld-NMR Spektrometern hat sich in den letzten Jahren ein stark wachsender Markt für kompakte Benchtop-NMR Geräte auf Permanentmagnetbasis entwickelt. Die geringeren Anschaffungs- und Betriebskosten, sowie die einfache Bedienbarkeit erlaubt es auch kleineren Unternehmen in diese Analysenmethode einzusteigen. Weiterhin besteht die Möglichkeit diese mobilen Systeme näher an die Produktion zu bringen, welches von der klassischen Qualitätskontrolle bis hin zur Online-Prozesskontrolle als vollautomatisierter Analysator reicht. Die geringere Feldstärke der Systeme erfordert hier oft den Einsatz modellbasierter Ansätze zur Spektrenauswertung (z.B. Indirect Hard Modeling).
Dieser Beitrag gibt eine Übersicht über aktuelle Anwendungen und Entwicklungen der qNMR von der universellen, hochgenauen Labormethode bis hin zur robusten Anwendung als Online-Analysator im Feld.
Compact nuclear magnetic resonance (NMR) instruments make NMR spectroscopy and relaxometry accessible in industrial and harsh environments for reaction and process control. An increasing number of applications are reported. Robust field integration of NMR systems have to face explosion protection or integration into process control systems with short set-up times. Tis paves the way for industrial automation in real process environments.
Automated data preparation and analysis are cornerstones for a breakthrough of NMR techniques for process control. Particularly, robust chemometrics as well as automated signal processing methods have to be (further) developed especially for NMR spectroscopy in process control. This becomes even more important for so called “smart sensors” providing the basis for the future project “Industrie 4.0”, and Industrial Internet of Things (IIoT), along with current requirements to process control, model based control, or soft sensing. Data analysis techniques are available but currently mostly used for off-line data analysis to detect the causes of variations in the product quality.
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.
In case study one of the CONSENS project, two aromatic substances were coupled by a lithiation reaction, which is a prominent example in pharmaceutical industry. The two aromatic reactants (Aniline and o-FNB) were mixed with Lithium-base (LiHMDS) in a continuous modular plant to produce the desired product (Li-NDPA) and a salt (LiF). The salt precipitates which leads to the formation of particles. The feed streams were subject to variation to drive the plant to its optimum.
The uploaded data comprises the results from four days during continuous plant operation time. Each day is denoted from day 1-4 and represents the dates 2017-09-26, 2017-09-28, 2017-10-10, 2017-10-17.
In the following the contents of the files are explained.
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'' (1.02 mm) was used as a flow cell in combination with a 5 mm glass Dewar tube inserted into a benchtop MR-NMR spectrometer with a 1H Larmor frequency of 43.32 MHz and 40.68 MHz for 19F. For the first time, quasi-simultaneous proton and fluorine NMR spectra were recorded with a series of alternating 19F and 1H 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 500 MHz 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 1.02 mm was characterised regarding the limit of detection (LOQ (1H) = 0.335 mol L-1 and LOQ (19F) = 0.130 mol L-1 for trifluoroethanol in D2O (single scan)) and maximum quantitative flow rates up to 0.3 mL min-1. Thus, a series of single scan 19F and 1H NMR spectra acquired with this simple set-up already presents a valuable basis for quantitative reaction monitoring.
A big problem with the chemistry literature is that it is not standardized with respect to precise operational parameters, and real time corrections are hard to make without expert knowledge. This lack of context means difficult reproducibility because many steps are ambiguous, and hence depend on tacit knowledge. Here we present the integration of online NMR into an automated chemical synthesis machine (CSM aka. “Chemputer” which is capable of small-molecule synthesis using a universal programming language) to allow automated analysis and adjustment of reactions on the fly. The system was validated and benchmarked by using Grignard reactions which were chosen due to their importance in synthesis. The system was monitored in real time using online-NMR, and spectra were measured continuously during the reactions. This shows that the synthesis being done in the Chemputer can be dynamically controlled in response to feedback optimizing the reaction conditions according to the user requirements.
The departure from the current automation landscape to next generation automation concepts for the process industry has already begun. Smart functions of sensors simplify their use and enable plug-and-play integration, even though they may appear to be more complex at first sight. Smart sensors enable concepts like self-diagnostics, self-calibration, and self-configuration/parameterization whenever our current automation landscape allows it. Here we summarize the currently discussed general requirements for process sensors 4.0 and introduce a smart online NMR sensor module as example, which was developed for an intensified industrial process funded by the EU’s Horizon 2020 research and innovation programme (www.consens-spire.eu).
Ugly Spectra and Lousy interfaces – Challenges for Compact NMR Spectroscopy in Process Control
(2016)
With the introduction of advanced process analytical technology, the closeness of key process variables to their limits can be directly controlled and the product can be classified or even released in real time.
Compact NMR instruments can make NMR spectroscopy accessible in industrial and harsh environments for process control.
Bei der Entwicklung pharmazeutischer Wirkstoffe werfen Substanzen mit einer geringen Löslichkeit, Auflösungsrate und damit einhergehend schlechten Bioverfügbarkeit immer größere Probleme auf. Diese Eigenschaften und nicht etwa toxikologische Eigenschaften oder schlechte Wirksamkeit sorgen dafür, dass es weniger als 1 % aller Wirkstoffe bis in die Markteinführung schaffen. Eine Reihe von Ansätzen zur Verbesserung der schlechten Wasserlöslichkeit konnten bereits etabliert werden. Hierunter zählen die gezielte Salzbildung bzw. Salzscreening, Solubilisierung mit Cosolventien oder die Nutzung von Polymeren als mögliche Transportwege. Eine weitere Möglichkeit bietet die Bildung verschiedener polymorpher Formen, sowohl der Einzelkomponente als auch von den verschiedenen Mehrkomponentenverbindungen.
Validation report on NMR
(2017)
The departure from the current automation landscape to next generation automation concepts for the process industry has already begun. Smart functions of sensors simplify their use and enable plug and play integration, even though they may appear to be more complex at first sight. Smart sensors enable concepts like self-diagnostics, self-calibration, and self-configuration/ parameterization whenever our current automation landscape allows it.
Here we summarize the currently discussed general requirements for process sensors 4.0 and introduce a smart online NMR sensor module as example, which was developed for an intensified industrial process funded by the EU’s Horizon 2020 research and innovation programme (www.consensspire.eu).