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首页> 外文期刊>Geoderma: An International Journal of Soil Science >The use of spin counting for determining quantitation in solid state 13C NMR spectra of natural organic matter: 1. Model systems and the effects of paramagnetic impurities.
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The use of spin counting for determining quantitation in solid state 13C NMR spectra of natural organic matter: 1. Model systems and the effects of paramagnetic impurities.

机译：使用自旋计数确定天然有机物的固态13C NMR光谱中的定量：1.模拟系统和顺磁性杂质的影响。

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The degree of quantification achieved in the solid state 13C NMR spectra of a number of organic materials, an HF-treated soil, and a whole soil, was determined for both cross-polarization (CP) and Bloch decay (BD) techniques using spin-counting experiments. The percentage of potential 13C NMR signal which was actually observed (Cobs) was in the range 79-107% for the BD technique and in the range 29-103% for the CP technique. A number of materials, including cellulose, pectin, lignin, and palmitic acid gave quantitative spectra using both CP and BD. A second group, including chitin, collagen, and the HF-treated soil gave quantitative BD spectra, but significantly diminished CP spectra (Cobs-CP=66-75%). A third group including charcoal, a commercialhumic acid, and the whole soil gave significantly diminished BD spectra (Cobs-BD=79-87%) and severely diminished CP spectra (Cobs-CP=29-35%). Signal losses in the CP spectra were attributed to rapid relaxation rates (short T1pH) and/or slow magnetization build-up rates (long TCH). The spin dynamics of the CP experiment were studied and a new method for correcting for differences in TlpH between the sample and the reference in CP spin-counting experiments was developed. Signal produced by the Kel-F rotor end-caps was significant for the BD spectra and a correction for the end-cap spectrum was required prior to spin counting. The low 1H content of the fluorinated Kel-F polymer ensured that the contribution of end-caps to the CP spectra was insignificant. The effects of paramagnetic cations on quantitation in solid state NMR spectra was investigated by doping model compounds with paramagnetic impurities. Three mechanisms, which bring about signal loss and operate on three different length scales, were identified. The magnitude of the signal loss brought about by a paramagnetic material was shown to be dependent on both the type of cation involved and on the intimacy of contact with the organic matrix. Chemically bound paramagnetic cations resulted in large signal losses in the CP spectrum, whereas paramagnetic salts in a physical mixture with an organic material affected both CP and BD spectra equally.
机译：对于多种有机材料，经HF处理的土壤以及整个土壤，在固态13C NMR光谱中均采用旋转极化法（CP）和Bloch衰减（BD）技术进行了定量测定计数实验。对于BD技术，实际观测到的潜在13C NMR信号百分数（Cobs）在79-107％范围内，对于CP技术在29-103％范围内。使用CP和BD可以对多种材料（包括纤维素，果胶，木质素和棕榈酸）进行定量光谱分析。第二组，包括几丁质，胶原蛋白和经过HF处理的土壤，给出了定量的BD光谱，但CP光谱显着减小（Cobs-CP = 66-75％）。第三组包括木炭，商业腐殖酸和整个土壤，其BD光谱显着降低（Cobs-BD = 79-87％），CP光谱显着降低（Cobs-CP = 29-35％）。 CP光谱中的信号损失归因于快速弛豫速率（较短的T1pH）和/或缓慢的磁化积累速率（较长的TCH）。对CP实验的自旋动力学进行了研究，并开发了一种校正CP自旋计数实验中样品与参比样品之间TlpH差异的新方法。由Kel-F转子端盖产生的信号对于BD光谱很重要，在旋转计数之前需要对端盖光谱进行校正。氟化Kel-F聚合物的1H含量低，可确保端盖对CP光谱的贡献不明显。通过用顺磁性杂质掺杂模型化合物，研究了顺磁性阳离子对固态NMR光谱定量的影响。确定了三种导致信号丢失并在三种不同长度尺度上运行的机制。由顺磁性材料引起的信号损失的大小已显示出取决于所涉及的阳离子的类型以及与有机基质接触的紧密度。化学键合的顺磁阳离子在CP光谱中导致大量信号损失，而与有机材料的物理混合物中的顺磁盐对CP和BD光谱的影响均相同。

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