Method for amino acid analysis and system for amino acid analysis

A system for separating a basic amino acid from a non-basic amino acid in a mixture of a plurality of amino acids comprising the basic amino acid and the non-basic amino acid, the system comprising:

• an eluent having a composition that comprises:
• a polybasic acid, a cation source, and water, having a pH in a range of 5.0 or lower at a temperature of 25° C., and being only one eluent present in the system and having a same composition therein;
• a separation column packed with a cation exchange resin and configured so that a sample comprising the mixture of the plurality of amino acids passes through the separation column with the eluent, thereby the basic amino acid and the non-basic amino acid being eluted separately;
• a heater configured to heat the separation column by applying a temperature gradient including a temperature region of 100° C. or higher;
• a pressurizer configured to flow the sample together with the eluent through the separation column by adding pressure to the separation column;
• and
• a detector configured to detect each of the separately eluted amino acids from the separation column,
• wherein the cation source is at least one salt of an alkali metal selected from the group consisting of a lithium (Li) salt and a sodium (Na) salt.