Chapter 2 - Quantitative NMR in the Solution State NMR

Abstract

This chapter assesses the scope and application of quantitative NMR. It enables a unique and quantitative determination of the relative amount of molecular groups, thus offering a tool to quantify entire substances even in mixtures. Quantitative NMR spectroscopic applications received major attention, supported by the technical progress of modern NMR techniques that overcame the problems of comparatively low sensitivity. This lead to a reduction of the previously widespread skepticism toward qNMR results. The most important fundamental relation of qNMR is that the signal response in a spectrum is directly proportional to the number of nuclei generating the corresponding resonance line. NMR spectra include only information about the ratio of intensities. However, adding a standard to a mixture, absolute results of analysis such as assays, contents, or concentrations can be obtained. qNMR has found widespread applications, particularly due to the possibility to determine structures at a molecular level, relatively short measuring times, its nondestructive character, no prior isolation of the analyte in a mixture, which means rather easy sample preparation and handling, and the unique combination of being both a powerful method of performing structural analysis and a competitive quantitative analytical tool with the ability to be a potential primary ratio method. However, poor sensitivity in comparison to other spectroscopic and chromatographic methods is the main disadvantage of qNMR.