Methionine is an important essential amino acid for animals. Methionine hydroxy analogues can be converted into methionine in animal bodies and exert their nutritional effects. In addition, it can also function as a component of several important enzymes (or as a cofactor) in animal bodies. Used as a rumen protein source for ruminants and an acidifier for piglet diets, it can inhibit bacteria, reduce heat stress, and decrease nitrogen excretion, protecting the environment. In addition, methionine is an important amino acid in poultry feed, which can effectively improve egg production rate. We use potentiometric titration to measure the content of basic copper chloride in feed additives, which is more accurate and faster.