Abstract: An analytical method was established for the simultaneous determination of glutathione and free amino acids in shellfish using a fully automatic amino acid analyzer. The extraction of the analytes was carried out using 0.02 mol/L hydrochloric acid solution as the extraction solvent followed by protein precipitation with 5% sulfonic acid solution. The buffer composition and the elution procedure were optimized at the same time. The linear range, limit of detection (LOD), precision and recovery rate of the method were determined. The results showed that good separation of glutathione and free amino acids in shellfish was achieved by this method with a good linear relationship. The correlation coefficients of the calibration curves were between 0.999 1 and 0.999 9. The minimum LODs at a signal to noise ratio (RSN) of 3 ranged from 0.07 to 0.27 μmol/L. The average recovery rates of spiked samples were between 86.40% and 102.42%. The relative standard deviations (RSDs) of intra-day and inter-day assays were 0.31%–0.73% and 1.14%–2.60%, respectively. Free amino acids were abundant in muscle tissue of four shellfish species, and their total free amino acid contents in decreasing order were clam (1 396.39 mg/100 g) > Cyclina sinensis (1 016.04 mg/100 g) > razor clam (911.15 mg/100 g) > oyster (287.01 mg/100 g). The main free amino acids were taurine, glutamic acid, alanine, and arginine. The glutathione contents of Cyclina sinensis, clam, razor clam and oyster were 103.20, 82.53, 61.77, and 33.37 mg/100 g, respectively. This method is suitable for the determination of glutathione and free amino acids in shellfish.

Key words: shellfish muscle, glutathione, free amino acids, automatic amino acid analyzer