Concentration Measurement of Amino Acid in Aqueous Solution by Quantitative 1 H NMR Spectroscopy with Internal Standard Method.

We describe a procedure to determine concentrations of amino acid standard solutions by quantitative NMR spectroscopy using an internal standard. The measurement samples were prepared by solvent exchange to remove any intense solvent signal in the 1 H NMR spectra. The method was demonstrated on valine aqueous solutions of different concentrations. The accuracy of the measured concentrations that fell well within the range of the expanded uncertainty is also discussed. All of the results are in good agreement with the preparation values. We believe that this approach should be useful to determine the concentrations of standard solutions whose solute components are difficult to weigh because of extremely small amount or hygroscopicity.