Quantitative Determination of Glycine, Alanine, Aspartic Acid, Glutamic Acid, Phenylalanine, and Tryptophan by Raman Spectroscopy

ABSTRACT

The development of a new quantitative method for amino acids using Raman spectroscopy is reported. Raman spectra of glycine, alanine, aspartic acid, glutamic acid, phenylalanine, and tryptophan were measured. The band ratio between the Raman intensity of the amino acid and that of acetonitrile as an external standard was calculated to remove the influence of factors such as laser power intensity and instrumental effects. The calibration curves were obtained by plotting the band ratios against the concentrations of the amino acids. The curves were linear with coefficient correlations of over 0.99 for all amino acids. The Raman spectra of known concentration samples were measured to confirm the reproducibility of this method. The relative errors were small, indicating that the concentrations of amino acids can be determined using Raman spectroscopy. The limits of detection and quantitation were determined as thrice and 10 times the standard deviation of the background signal to be 0.007 and 0.02 mol L⁻¹, respectively. Raman spectra of aspartic acid at 0.02 mol L⁻¹ were measured several times and the uncertainty was 7%.

KEYWORDS:

• Amino acid
• limits of detection and quantitation
• quantitative analysis
• Raman spectroscopy
• vibrational mode

Acknowledgments

The authors thank Mr. Kyohei Kawasumi for his assistance in the calculations. The authors thank Miss Maki Higano and Miss Miyuki Yaginuma for their assistance during the experiments.