使用UDEFT（均匀驱动平衡傅里叶变换）改进固体上${}^{29}$ Si NMR实验的灵敏度和定量
Improved sensitivity and quantification for ${}^{29}$Si NMR experiments on solids using UDEFT (Uniform Driven Equilibrium Fourier Transform)
摘要：
我们证明了利用均匀驱动平衡傅里叶变换（UDEFT）技术来提高魔角旋转（MAS）下一维${}^{29}$ Si NMR实验的灵敏度和定量化的可能性。我们推导出一个解析表达式的信噪比的UDEFT和单脉冲（SP）实验归入瞬态和稳态制度的贡献。使用数值自旋动力学模拟和实验${}^{29}$富硅无定形二氧化硅和硼硅酸盐玻璃，我们表明，59 ${}_{180}$ 298 ${}_{0}$ 59 ${}_{180}$再聚焦复合$π$脉冲和绝热反演使用双曲正切/正切调制提高的鲁棒性的UDEFT技术的射频不均匀性，偏移和化学位移各向异性。这些脉冲与两步相位循环相结合，限制了脉冲缺陷和受激回波产生的伪影。实验比较了SP，UDEFT和CPMG（Carr-Purcell Meiboom-Gill）技术在功能化和非功能化介孔二氧化硅上的灵敏度。此外，对阻燃材料的实验证明，UDEFT技术提供了一个更好的量化的${}^{29}$ Si网站与更高的灵敏度比SP方法。
英文摘要：
We demonstrate the possibility to use UDEFT (Uniform Driven Equilibrium Fourier Transform) technique in order to improve the sensitivity and the quantification of one-dimensional ${}^{29}$Si NMR experiments under Magic-Angle Spinning (MAS). We derive an analytical expression of the signal-to-noise ratios of UDEFT and single-pulse (SP) experiments subsuming the contributions of transient and steady-state regimes. Using numerical spin dynamics simulations and experiments on ${}^{29}$Si-enriched amorphous silica and borosilicate glass, we show that 59${}_{180}$298${}_{0}$59${}_{180}$ refocusing composite $π$-pulse and the adiabatic inversion using tanh/tan modulation improve the robustness of UDEFT technique to rf-inhomogeneity, offset, and chemical shift anisotropy. These pulses combined with a two-step phase cycling limit the pulse imperfections and the artifacts produced by stimulated echoes. The sensitivity of SP, UDEFT and CPMG (Carr-Purcell Meiboom-Gill) techniques are compared experimentally on functionalized and non-functionalized mesoporous silica. Furthermore, experiments on a flame retardant material prove that UDEFT technique provides a better quantification of ${}^{29}$Si sites with higher sensitivity than SP method.
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