Karlsruhe Institute of Technology (KIT), Institute for Chemical Technology and Polymer Chemistry, Engesserstr. 18, 76131 Karlsruhe, Germany.
Université de Nantes, CNRS, CEISAM UMR 6230, F-44000 Nantes, France.
J Magn Reson. 2021 Feb;323:106889. doi: 10.1016/j.jmr.2020.106889.
The characterisation of polymeric materials in their full complexity of chain length, monomeric composition, branching and functionalization is a tremendous challenge and is best tackled by tailored multi-dimensional coupled analytical and detection techniques. Herein, we focus on the improvement of an affordable but information rich 2D-method for polymer analysis: the online hyphenation of benchtop H NMR spectroscopy with size exclusion chromatography (SEC). The main benefit of this approach is correlated information of chain length (SEC) to chemical composition (H NMR). Our setup combines SEC onflow with a benchtop NMR spectrometer at 43 or 62 MHz with chemical shift resolution as a robust detector. A detailed comparison of the two instruments is included considering, that only the 43 MHz instrument is equipped with a dedicated z-gradient enabling pulse sequences such as WET. The main challenge of this method is the very low concentration of species of interest after chromatographic separation. At typical SEC conditions, the analyte dilution is typically more than a factor of 1000:1 in a protonated solvent. Therefore, an efficient solvent signal suppression is needed. In this article, several suppression pulse sequences are explored like WET, WEFT, JNR and a simple one-pulse approach - some for the first time on this hardware. By choosing an optimal method, signal strength ratios of solvent to analyte of 1:1 or better are achievable on flow. To illustrate the broad range of possible applications, three typical cases of analyte to solvent signal proximity (no overlap, partial and full overlap) are discussed using typical polymers (PS, PMMA, PEMA) and solvents (chloroform and THF). For each case, several suppression methods are compared and evaluated using a set of numerical criteria (analyte signal suppression and broadening, solvent signal suppression, remaining solvent signal width).
对聚合物材料进行全长度、单体组成、支化和功能化的特征描述是一个巨大的挑战，最好通过定制的多维分析和检测技术来解决。在此，我们专注于改进一种经济实惠但信息丰富的二维聚合物分析方法：台式核磁共振波谱与尺寸排阻色谱（SEC）的在线联用。这种方法的主要优点是将链长（SEC）的相关信息与化学组成（NMR）联系起来。我们的装置将 SEC 与 43 或 62MHz 的台式 NMR 光谱仪结合，使用化学位移分辨率作为强大的检测器。我们考虑了两种仪器的详细比较，因为只有 43MHz 的仪器配备了专用的 z 梯度，可实现 WET 等脉冲序列。该方法的主要挑战是在色谱分离后，感兴趣的物种浓度非常低。在典型的 SEC 条件下，分析物在质子化溶剂中的稀释度通常超过 1000:1。因此，需要有效的溶剂信号抑制。在本文中，我们探索了几种抑制脉冲序列，如 WET、WEFT、JNR 和一种简单的单脉冲方法——有些是在这种硬件上首次应用。通过选择最佳方法，可以在流动相中实现溶剂与分析物信号强度比为 1:1 或更好。为了说明可能的应用范围广泛，我们使用三种典型的分析物与溶剂信号接近程度（无重叠、部分重叠和完全重叠）的情况（PS、PMMA、PEMA）和溶剂（氯仿和 THF）进行了讨论。对于每种情况，我们使用一组数值标准（分析物信号抑制和展宽、溶剂信号抑制、剩余溶剂信号宽度）比较和评估了几种抑制方法。
