Evaluation of the Hygroscopicity of Amino Acids Reference Materials by Thermogravimetric Analysis

Abstract

Amino acids are essential nutriments and the most basic construct matter of a living organisms. Thus, the amino acid content is determined in various fields. However, reference materials are necessary for making calibration curves for quantitative analysis, such as chromatography methods. Therefore, a variety of amino acids standard solution that is traceable to the International System of Units (SI) have a wide field of demand. To make standards solution of the precise concentration, which requires reference materials with accurate purity and precise weighing methods. However, for precise weighing, an appropriate weighing environment is neccessary. It was known that to some amino acids have strong hygroscopicity, but it wasn't known in a quantitative form. Therefore, previously weighing environment is empirically-determined. We measured the hygroscopicity of amino acids for deciding on a quantitatively-assessed weighing environment to obtain a precise amount of amino acids, and to prepare a standard solution with precise concentrations. We estimated the hygroscopicity and sublimability of 41 amino acids using temperature and humidity-controlled thermobalance equipment. As a result, when it was below a relative humidity 30 % (at 25 °C), we can weigh a precise amount of 41 amino acids. We can prepare an amino acids standard solution with precise concentrations. We create a methodology for determining a quantitatively-assessed weighing environment to obtain the precise mass or concentration of the standard solution. This methodology is effective and it can be applied widely.