Laboratory of Engineering Thermodynamics (LTD), Technische Universität Kaiserslautern (TUK), Kaiserslautern, Germany.
Department of Chemical and Process Engineering, University of Canterbury, Christchurch, New Zealand.
Magn Reson Chem. 2021 Mar;59(3):221-236. doi: 10.1002/mrc.5095. Epub 2020 Sep 28.
Nuclear magnetic resonance (NMR) spectroscopy is widely used for applications in the field of reaction and process monitoring. When complex reaction mixtures are studied, NMR spectra often suffer from low resolution and overlapping peaks, which places high demands on the method used to acquire or to analyse the NMR spectra. This work presents two NMR methods that help overcome these challenges: 2D non-uniform sampling (NUS) and a recently proposed model-based fitting approach for the analysis of 1D NMR spectra. We use the reaction of glycerol with acetic acid as it produces five reaction products that are all chemically similar and, hence, challenging to distinguish. The reaction was measured on a high-field 400 MHz NMR spectrometer with a 2D NUS-heteronuclear single quantum coherence (HSQC) and a conventional 1D H NMR sequence. We show that comparable results can be obtained using both 2D and 1D methods, if the 2D volume integrals of the 2D NUS-HSQC NMR spectra are calibrated. Further, we monitor the same reaction on a low-field 43 MHz benchtop NMR spectrometer and analyse the acquired 1D H NMR spectra with the model-based approach and with partial least-squares regression (PLS-R), both trained using a single, calibrated data set. Both methods achieve results that are in good quantitative agreement with the high-field data. However, the model-based method was found to be less sensitive to the training data set used than PLS-R and, hence, was more robust when the reaction conditions differed from that of the training data.
核磁共振（NMR）光谱广泛应用于反应和过程监测领域。当研究复杂的反应混合物时，NMR 光谱通常会受到低分辨率和重叠峰的影响，这对用于获取或分析 NMR 光谱的方法提出了很高的要求。这项工作提出了两种有助于克服这些挑战的 NMR 方法：二维非均匀采样（NUS）和最近提出的用于分析一维 NMR 光谱的基于模型的拟合方法。我们使用甘油与乙酸的反应作为实例，因为它产生了五种化学性质相似的反应产物，因此难以区分。该反应在一台高场 400 MHz NMR 光谱仪上进行，使用二维 NUS-异核单量子相干（HSQC）和常规一维 H NMR 序列进行测量。我们表明，如果校准二维 NUS-HSQC NMR 光谱的二维体积积分，则可以使用二维和一维方法获得可比的结果。此外，我们在低场 43 MHz 台式 NMR 光谱仪上监测相同的反应，并使用基于模型的方法和偏最小二乘法回归（PLS-R）分析获得的一维 H NMR 光谱，这两种方法均使用单个校准数据集进行训练。这两种方法都得到了与高场数据高度定量一致的结果。然而，与 PLS-R 相比，基于模型的方法对所使用的训练数据集的敏感性较低，因此在反应条件与训练数据不同时更为稳健。
