Figure 2: Chromatograms of an amino acid certified reference material (NIST 2389a) diluted in 0.1 M HCl with added Trp (1.25 mM), Gln (2.5 mM), and Asn (2.5 mM). Please note that 17 of these 20 amino acids are not visible in this time window. This is mainly due to weak retention and not due to lack of detectability because most amino acids possess a significant absorbance at 215 nm. In addition, a blank run is shown (dashed).