利用相位步进脉冲消除探头13C NMR背景信号

Suppressing Background 13C NMR Signal From the Probe Head by Phase Incremented Pulses

由静态探头线圈外有机材料产生的^13C NMR背景信号强度大,化学位移范围广(dC 20~250),此背景信号在交叉极化实验中还可被增强,并随着样品信号的累积而累积,严重影响谱图分析.将相位步进脉冲引入交叉极化实验(称为PIPCP)中可以有效去除经交叉极化增强的^13C NMR背景信号,但样品信号不受影响.这是由于经过相位步进脉冲后,线圈外相位严重畸变,而且线圈外锁定场强度急剧降低,来自探头材料的^13C NMR背景信号无法有效地进行交叉极化.而对于被测样品甘氨酸来说,由于I核和S核之间强烈的偶极耦合作用,所加相位步进脉冲对锁定场强度的影响只有1.4%.

The background^13C NMR signal originated from the organic materials in the probe head cross-polarizes from 1 H nucleus to^13C nucleus.This background^13C NMR signal is very broad(δC 20~250)and accumulates as the sample signal accumulating.Hartman-Hahn cross polarization with phase-incremented pulses in the S spin channel(denoted as PIPCP)is developed to suppress this background signal.The application of PIPCP results in severe phase distortion outside the radio frequency coil such that the background^13C NMR signal cannot cross polarize and thus be suppressed.In comparison,depending on the dipolar coupling constant between 1 H and^13C nuclei,PIPCP induces only a small amount of Hartman-Hahn mismatch(1.4%)to the desired signals.