SI-traceable Purity Evaluation of Non-protein Amino Acid as Reference Materials by Using H NMR Spectroscopy

In recent years, it was become increasingly important to conduct quantitative analyses of several kinds of protein and non-protein amino acids in the human blood. By doing so, it is possible to detect cancer focus positivity at an early stage by monitoring profile of their concentrations. In clinical tests that strongly require high reliability of analytical values, it is essential to use amino acid reference materials that are traceable to the International System of Units (SI). However, SI-traceable reference materials of non-protein amino acids are not generally supplied worldwide. Although it is generally used in the titration method for purity evaluations of amino acid reference materials, purity evaluations using this method require much time and a large amount of sample. On the other hand, Nuclear Magnetic Resonance (NMR) spectroscopy is a rapid quantitative method that is not only SI-traceable, but also requires a small amount of the sample. In this study, we demonstrated purity evaluations of 20 kinds of non-protein amino acids by using NMR. To verify the analytical value, a titration method was used. From our results, the accuracy of the analytical value was evaluated to be approximately 1 % by optimizing the experimental conditions for each amino acid, such as the kinds of solvent. Furthermore, the difference in the analytical values between 'H NMR and titration was 0.5 % or less. Therefore, it was confirmed to able to perform rapid and accurate evaluations of the purity of non-protein amino acid reference materials by using 'H NMR spectroscopy.