Chapter 5: Applications of High-resolving Power, High-accuracy Mass Spectrometry for the Structural Elucidation of Natural Products

While the 1D and 2D nuclear magnetic resonance (NMR) experimental methods described in other chapters of this book are essential for the detailed structure elucidation of natural products, mass spectrometry is generally recognized as a method that can enhance both the speed and accuracy of such work. Determination of the molecular weight to nominal mass using simple and commonly available low-performance mass spectrometers can help confirm a structure proposed from NMR studies. As discussed in this chapter, an accurate mass measurement of the molecular mass with <5 ppm accuracy is even more useful, as such measurements can be used to determine, or place limits on, the possible molecular formulae of the unknown. Recently, mass spectrometers capable of mass measurement accuracies of <5 ppm in both single and tandem and mass spectrometry modes have become widely available (e.g. Orbitrap, quadrupole time-of-flight, and Fourier transform mass spectrometers). These different types of mass spectrometers are discussed briefly, and some examples are given of how accurate mass measurements of both the molecular ion and fragment ions of natural products can improve the speed and accuracy of natural product structure determination.