A rapid, accurate, and precise NMR analytical method for the analysis of phenylglycine, dihydrophenylglycine, tetrahydrophenylglycine, and cyclohexylglycine in combination with each other was developed. The method is based on the integration of the NMR signal characteristic of each component relative to the signal from tetramethylammonium bromide, which is added as an internal standard. No prior separation of the four components is required.