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Amino Acid Analysis

Proteins and peptides are large macromolecules consisting of covalently bonded amino acids. Proteins commonly exist as folded structures, while peptides are shorter linear polymers consisting of only a few amino acids. Amino acid analysis refers to the methodology used to determine the individual amino acids in a protein or peptide that may be part of—for example—a pharmaceutical preparation. Analysis of amino acid content can be used to support protein or peptide structure, evaluate fragmentation strategies, or detect atypical amino acids that may be present. It is necessary to hydrolyze the protein of interest, and the choice of procedures is key to accurate analysis as some sensitive amino acids may be destroyed during the hydrolysis. After hydrolysis, the hydrolyzing reagents are removed (typically by evaporation) and the hydrosylate is reconstituted in water or other compatible solvent. Because most free amino acids are poor chromophores, they cannot be directly detected at low concentrations using ultraviolet (UV), visible (vis), or fluorescence detection. Therefore the hydrolysate must first be derivatized with a chromophoric or fluorometric reagent before detection. This derivatization can be performed either before chromatography (precolumn derivatization) or after chromatography (postcolumn derivatization). Both pre- and postcolumn derivatization methods are costly for both reagents and labor, add risk of toxic chemical exposure to personnel, and require hazardous waste removal. Electrochemical detection is a good alternative, that doesn't require derivatization after hydrolysis.

Dionex AAA-Direct

The Thermo Scientific* Dionex* AAA-Direct* system is a highly sensitive and direct-detection type of amino acid analyzer that requires no sample derivatization. The Dionex AAA-Direct instrument uses integrated pulsed amperometry (IPAD)—a type of electrochemical detection—to directly detect amino acids. The Dionex AAA-Direct also provides complete separation of all common amino acids using anion-exchange chromatography (Thermo Scientific Dionex AminoPac* PA10 column).