The Improved Solid-state NMR Quantitative Method on the Bases of Multiple-cross Polarization Technique

Recently, multiple-cross polarization (multiCP) has attracted much interest owing to its favorable performance as a solid-state nuclear magnetic resonance quantitative method. Relating investigations revealed that the setup of multiCP parameters relies on the properties of the samples. Diverse types of samples require different parameters. To improve the tolerance to sample properties, an improved method named MLGCP-1 was proposed in this work, which employed Lee-Goldburg cross polarization technique. L-alanine, L-valine and their mixtures were chosen as model samples to evaluate the performance of MLGCP-1 method. multiCP experiments were also conducted for comparison. Based on the test of molecular group ratio, it was revealed that the range of contact time tp of MLGCP-1 was larger than that of multiCP, which improved from 1.0~1.3 ms to 0.8~2.0 ms. Moreover, according to the study of L-valine and mixtures, it was revealed that the range of tp was influenced by the difference of cross relaxation time TCH. Large TCH difference limited tp range for quantification. This manner was in accordance with multiCP. However, the tp range of MLGCP-1 was markedly enlarged in comparison with multiCP, presenting higher tolerance to the sample properties.