Method for measuring content of cysteine in compound amino acid injection

The invention provides a method for determining the content of cysteine in a compound amino acid injection, and belongs to the technical field of quantitative detection. The method comprises the following steps: (1) adopting a 2wt% phosphoric acid solution as a diluent, and adding a cysteine negative sample solution to prepare a cysteine reference substance solution; (2) adding a 2wt% phosphoric acid solution into the compound amino acid injection, and diluting to obtain a test solution; (3) high performance liquid chromatography is adopted for detection, a mobile phase A comprises 0.02 mol/L of monopotassium phosphate and 0.01 mol/L of sodium nonane sulfonate, and the pH is 2.3; the mobile phase A is acetonitrile, the mobile phase B is acetonitrile, and the gradient elution procedure is as follows: 0-25 minutes, 100% of the mobile phase A and 0% of the mobile phase B; 25.1-35 min, 60% of a mobile phase A and 40% of a mobile phase B are adopted; 35.1-55 min, 100% of a mobile phase A and 0% of a mobile phase B