Second, touch, true methionine has a special smell (hydroxyl has a special smell of hydroxyl), which tastes a little sweet with the mouth, feels smooth and has no rough feeling. False methionine smells bad, some have ammonia stimulation or aromatic smell, and it is rough and not greasy.

Dissolve for the third time: take about 65438 0 g of methionine, add 50ml of distilled water, gently stir, shake well, and let stand. The true methionine solution is clear and transparent without precipitation. If the solution is turbid or precipitated, the sample is defective. Or adopt the following methods.

1. Take 25 mg methionine sample and add saturated sulfuric acid solution of anhydrous copper sulfate. The solution should be yellow. If it is colorless or other colors, it is counterfeit.

2. Weigh 3 mg of sample, dissolve it in 5 ml of water, add 2 ml of sodium hydroxide test solution, mix well, add 0.3 ml of sodium ferrocyanide solution (1 g sodium ferrocyanide dissolved in 20 ml of water), then shake well, place it at 35-40℃ for 10 minute, move it into ice water for 2 minutes, and add 2 mol/ml.

3. Prepare the sample into 1% aqueous solution, take 5ml, add 0. 1% ninhydrin test solution of 1ml, heat for 3min, add 20ml water, and let stand for 15min. The solution is blue-purple, while the counterfeit product is colorless.