There are several methods available to measure the amino acid content of a feed sample. Here are a few commonly used techniques:

Ion exchange chromatography: This method separates amino acids based on their charge and is widely used for amino acid analysis. The amino acids in the feed sample are first hydrolyzed to their individual components, and then separated using an ion exchange column. The separated amino acids can then be detected and quantified using a detector such as UV or fluorescence.

High-performance liquid chromatography (HPLC): This method separates amino acids based on their chemical properties and is also commonly used for amino acid analysis. The amino acids in the feed sample are again hydrolyzed and separated using an HPLC column. The separated amino acids are then detected and quantified using a UV or fluorescence detector.

Near-infrared spectroscopy (NIR): NIR is a non-destructive method that uses the absorption of light in the near-infrared region to determine the amino acid content of a sample. This method is fast, easy to use, and requires minimal sample preparation.

Enzymatic methods: There are several enzymatic methods available that can be used to measure specific amino acids in a feed sample. These methods involve the use of specific enzymes that react with a particular amino acid, producing a measurable signal.

Ultimately, the choice of method will depend on the resources available, the specific amino acid(s) of interest, and the accuracy and precision required for the analysis.

I agree with Lamia Fatima.

Also, depending on what you need, you may consider Kjeldahl (total nitrogen).

Many commercial labs routinely perform Amino Acid analysis for a very reasonable price. If you have

Use AAFCO (American Association of Feed Chemists) or AOAC (Association of Official Analytical Chemists) methods.

Sample prep greatly differs according to purpose in terms of free or bound AAs...Instrumental options were already suggested above.