The main organic acids contained in the flesh of lemons are citric acid and malic acid. The sourness of citrus fruit is the taste of citric acid. The figure shows the analysis of lemon juice by a high-performance liquid chromatography organic acid analysis system.

Analysis of Lemon Juice

Amino Acid Analysis System

High-Performance Liquid Chromatograph

Post-column fluorescence detection using an OPA reagent achieves at least an order of magnitude higher sensitivity than the ninhydryn method. After the amino acids are separated by ion-exchange chromatography, they are derivatized through reaction with an OPA reagent, and detected by fluorescence detection. This achieves highly accurate quantitation without the adverse effects of impurities that sometimes affect pre-column derivatization. This system is superior in terms of detection sensitivity, selectivity, and ease of operation, and is widely used for foods analysis and in other fields.