MacKinnon Neil, While Peter T, Korvink Jan G
Institute for Microstructure Technology - IMT, Karlsruhe Institute of Technology, Karlsruhe, Germany.
Department of Radiology and Nuclear Medicine, St. Olav's University Hospital, Trondheim, Norway.
J Magn Reson. 2016 Nov;272:147-157. doi: 10.1016/j.jmr.2016.09.011. Epub 2016 Sep 16.
Complex mixture analysis is routinely encountered in NMR-based investigations. With the aim of component identification, spectral complexity may be addressed chromatographically or spectroscopically, the latter being favored to reduce sample handling requirements. An attractive experiment is selective total correlation spectroscopy (sel-TOCSY), which is capable of providing tremendous spectral simplification and thereby enhancing assignment capability. Unfortunately, isolating a well resolved resonance is increasingly difficult as the complexity of the mixture increases and the assumption of single spin system excitation is no longer robust. We present TOCSY optimized mixture elucidation (TOOMIXED), a technique capable of performing spectral assignment particularly in the case where the assumption of single spin system excitation is relaxed. Key to the technique is the collection of a series of 1D sel-TOCSY experiments as a function of the isotropic mixing time (τ), resulting in a series of resonance intensities indicative of the underlying molecular structure. By comparing these τ-dependent intensity patterns with a library of pre-determined component spectra, one is able to regain assignment capability. After consideration of the technique's robustness, we tested TOOMIXED firstly on a model mixture. As a benchmark we were able to assign a molecule with high confidence in the case of selectively exciting an isolated resonance. Assignment confidence was not compromised when performing TOOMIXED on a resonance known to contain multiple overlapping signals, and in the worst case the method suggested a follow-up sel-TOCSY experiment to confirm an ambiguous assignment. TOOMIXED was then demonstrated on two realistic samples (whisky and urine), where under our conditions an approximate limit of detection of 0.6mM was determined. Taking into account literature reports for the sel-TOCSY limit of detection, the technique should reach on the order of 10μM sensitivity. We anticipate this technique will be highly attractive to various analytical fields facing mixture analysis, including metabolomics, foodstuff analysis, pharmaceutical analysis, and forensics.
在基于核磁共振（NMR）的研究中，经常会遇到复杂混合物分析。为了识别成分，光谱复杂性可以通过色谱法或光谱法来解决，后者更有利于减少样品处理要求。一种有吸引力的实验是选择性全相关光谱法（sel-TOCSY），它能够极大地简化光谱，从而提高谱峰归属能力。不幸的是，随着混合物复杂性的增加，分离出一个分辨率良好的共振峰变得越来越困难，并且单自旋系统激发的假设不再可靠。我们提出了TOCSY优化混合物解析法（TOOMIXED），这是一种能够进行谱峰归属的技术，特别是在单自旋系统激发假设放宽的情况下。该技术的关键是收集一系列作为各向同性混合时间（τ）函数的一维sel-TOCSY实验，从而得到一系列指示潜在分子结构的共振强度。通过将这些与τ相关的强度模式与预先确定的成分光谱库进行比较，就能够恢复谱峰归属能力。在考虑了该技术的稳健性之后，我们首先在模型混合物上测试了TOOMIXED。作为基准，在选择性激发孤立共振峰的情况下，我们能够高置信度地归属一个分子。在对已知包含多个重叠信号的共振峰进行TOOMIXED分析时，归属置信度并未受到影响，并且在最坏的情况下，该方法建议进行后续的sel-TOCSY实验以确认模糊的归属。然后在两个实际样品（威士忌和尿液）上演示了TOOMIXED，在我们的条件下确定了大约0.6mM的检测限。考虑到文献中关于sel-TOCSY检测限的报道，该技术的灵敏度应达到10μM左右。我们预计该技术对于面临混合物分析的各种分析领域将具有高度吸引力，包括代谢组学、食品分析、药物分析和法医学。
