Fig. 1: Schematic representation of the quantification method using NMR spectroscopy.
a Due to small sample sizes, detection of the NMR transient after spin excitation is accomplished by the use of magnetic flux-focusing Lenz lenses. b Since signal intensities are directly proportional to the spin density of each spin system (n(1H) and n(27Al))), this method provides a direct measurement of the spin density (spins per sample volume) in a microscopic specimen. Red (real part) and blue (imaginary part) curves represent free-induction decays of each spin system. Green curves are the respective magnitudes. c Moreover, abundant NMR-active nuclei in the same sample (e.g. 27Al) can be employed as internal reference standards, making this method fully stand-alone and non-destructive for trace-element quantification. The red, yellow and cyan balls represent oxygen, hydrogen and aluminum atoms, respectively. The generic crystal structure was generated using VESTA.
