Quantitative nuclear magnetic resonance: Experimental methods and typical applications

Quantitative nuclear magnetic resonance (qNMR) technology is a highly versatile and accurate quantitative analysis approach. Due to its merits, such as simple operation, no requirement for reference standards of the analytes, and the capacity to conduct structural analysis of the analytes and impurities simultaneously during quantitative analysis, it has found extensive applications in the quantitative analysis of materials such as pharmaceuticals, food, natural products, and metabolomics. The fundamental principle of quantitative nuclear magnetic resonance is that the number of atoms generating a specific resonance signal in different chemical environments is proportional to the intensity of the nuclear magnetic response signal, and the signal response of the same atomic nucleus in different molecules shows no discrepancy under optimized conditions. In this paper, we review the sample preparation procedures, experimental parameter optimization and data processing methods required in order to obtain accurate signal intensities and, hence, accurate quantitative results. Taking the two currently most typical ¹H qNMR applications, namely hydrogen quantitative NMR (¹H qNMR) analysis of low-abundance (concentration) substances and purity determination of high-purity substances (reference materials, etc.), as examples, we have highlighted relevant experimental methods and provide a general overview of the use of NMR quantitative analysis in various fields.