NMR is best known for its use in structure determination. The chemical structure of a small molecule dictates a rational spectrum. This is because the electronic structure, the bedrock of chemistry, is what determines the chemical shift, while the number of nuclei determine the coupling and relative intensities. These same properties result in NMR being excellent for quantification and identification. The peaks in the spectrum will appear in predictable locations in the spectrum and their intensities will be proportional to the number of nuclei in the sample. In other words, the peaks are a chemical signature and the sample concentration is proportional to the intensity of the NMR signal detected. Sample concentrations and purities can be easily measured from known peaks once the proportionality constant is calibrated using a reference of known concentration. Using these peak positions and relative intensities, the compounds, mixtures and impurities in a sample can be identified or quantified.