Effect of different matrices on physiological amino acids analysis by liquid chromatography: evaluation and correction of the matrix effect

Free amino acids in plasma, muscle and liver tissues were determined using the Pico-Tag method which involves HPLC and pre-column derivatization. A study of the accuracy in the determination is carried out by means of external calibration, standard-added calibration, Youden calibration and analyte recovery. It is conclusively shown that the method is affected by a proportional systematic error due to matrix effects, but not by a constant one. A new function named matrix-corrected calibration is proposed to correct for proportional bias when free analyte matrices for matrix-matched addition is unavailable.