采用火焰密封或不采用火焰密封核磁共振管:汽液平衡对变温实验精度的影响。

IF 1.9 3区 化学 Q3 CHEMISTRY, MULTIDISCIPLINARY Magnetic Resonance in Chemistry Pub Date : 2023-11-22 DOI:10.1002/mrc.5411
Derek Morrelli, Santanu Maitra, V. V. Krishnan
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引用次数: 0

摘要

在核磁共振实验中,控制样品的温度是至关重要的,特别是在测量动力学参数时。通常情况下,样品在核磁共振探头内的温度需要2 ~ 5min才能稳定在实验设定的固定值。然而,在某些情况下,核磁共振样管是火焰密封的,例如当使用挥发性溶剂,大气敏感样品或长期使用的校准样品时。当这些样品被放置在核磁共振探针内时,光谱仪控制核磁共振样品管的下部(液相)在固定温度下以气体流动,而上部(蒸汽)在环境温度下。这种探针设计在样品上产生独特的温度梯度,导致蒸汽压力积聚,特别是在密封的核磁共振管内。通过分析化学交换过程的温度依赖谱线形状变化,我们报告说,在标准实验条件下,样品温度可能需要2到3小时(而不是几分钟)才能稳定。液-气平衡过程的时间尺度要慢得多,半衰期超过35分钟,而获得每个光谱所需的时间为2分钟。这种现象完全是由于火焰密封核磁共振管的液-气平衡过程引起的,否则无法观察到。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

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To flame-seal or not to flame-seal NMR tubes: The role of liquid–vapor equilibria on the accuracy of variable temperature experiments

In NMR experiments, it is crucial to control the temperature of the sample, especially when measuring kinetic parameters. Usually, it takes 2 to 5 min for the temperature of the sample inside the NMR probe to stabilize at a fixed value set for the experiment. However, the NMR sample tubes are flame-sealed in some cases, such as when working with volatile solvents, atmosphere-sensitive samples, or calibration samples for long-term use. When these samples are placed inside the NMR probe, the spectrometer controls the lower portion (liquid phase) of the NMR sample tube with a gas flow at a fixed temperature, while the upper portion (vapor) is at ambient temperature. This probe design creates a unique temperature gradient across the sample, leading to vapor pressure build-up, particularly inside a sealed NMR tube. By analyzing the temperature-dependent spectral line shape changes of a chemical exchange process, we report that under standard experimental conditions, the sample temperature can take up to 2 to 3 h (instead of minutes) to stabilize. The time scale of the liquid–vapor equilibrium process is much slower, with a half-life exceeding 35 min, in contrast to the 2-min duration required to obtain each spectrum. This phenomenon is exclusively due to the liquid–vapor equilibrium process of the flame-sealed NMR tube and is not observable otherwise.

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来源期刊
CiteScore
4.70
自引率
10.00%
发文量
99
审稿时长
1 months
期刊介绍: MRC is devoted to the rapid publication of papers which are concerned with the development of magnetic resonance techniques, or in which the application of such techniques plays a pivotal part. Contributions from scientists working in all areas of NMR, ESR and NQR are invited, and papers describing applications in all branches of chemistry, structural biology and materials chemistry are published. The journal is of particular interest not only to scientists working in academic research, but also those working in commercial organisations who need to keep up-to-date with the latest practical applications of magnetic resonance techniques.
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