||Mitochondrial Citric Acid (CA) is the first intermediate product of the mitochondrial tricarboxylic acid cycle. The synthesis of acetyl CoA and oxaloacetate is catalyzed by citrate synthase. Its content is one of the main indicators of the strength of the tricarboxylic acid cycle. Cooperate with the determination of pyruvate content, pyruvate dehydrogenase activity, acetyl CoA content, citrate synthase activity and CA content, among which (1) the changes in pyruvate content and pyruvate dehydrogenase activity can reflect the progress of glycolysis, ( 2) Comprehensive analysis of pyruvate content, pyruvate dehydrogenase activity and acetyl CoA content changes can reflect the acetyl CoA provided by fatty acid β-oxidation pathway; (3) Acetyl CoA content, citrate synthase activity and CA content changes can reflect The status of the tricarboxylic acid cycle. CA produces α-keto acid (oxaloacetic acid) under the action of citrate lyase; under weak acid conditions, α-keto acid further reacts with phenylhydrazine to form the corresponding α-keto acid phenylhydrazone; α-ketone acid phenylhydrazone has an absorption peak at 330nm, and the degree of change in absorbance at this wavelength can reflect the content of CA.