PURPOSE: To reduce the consumption amount of reagents by using an HPLC part performing two-liquid gradient elution in the separation and quantification of amino acid obtained by performing derivation according to a precolumn method using a predetermine substance as an amino acid deriving reagent in a deriving part.

CONSTITUTION: An analyzer is constituted of a deriving part 1 performing the fluorescent derivation of amino acid (AA) by 4-thiocarbamyl-7- nitrobenzoflazane (NBITC), a separation column 3 for separating derived amino acid (NBTC-AA), a pump 7 for feeding reagents, a fluorometric detector 4 for detecting separated amino acid and a control and data processing part 5 performing the processing of a detected signal and the control of respective constitutional elements. A fluorescent substance is derived from a sample by NBITC to be sucked in a liquid feed system by a sample injector 2 and fed to the separation column 3 along with the eluent 6 sent by a pump 7 to be separated at every amino acid and the intensity of fluorescence thereof is measured by a detector 4 and the qualitative and quantitative analyzes of amino acid are carried out in the control and data processing part 5.