Typical Procedure: 5-10 µL aliquots of amino acid standards or unknown samples are mixed with 5 µL of a solution prepared by dissolving of o-phthalaldehyde (50 mg) in absolute MeOH (1.25 mL) followed by the addition of 2-mercaptoethanol (50 µL) and 0.4 M sodium borate (pH 9.5) (11.2 mL). After 1 min, 0.1 M sodium acetate (pH 7.0) (20-100 µL) are added, the solution mixed and a 20-µL sample is subjected to analysis.