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Modified Ninhydrin Reagents to Detect Colors of Amino Acid Zones on Thin-Layer Chromatographic Plates

Amino acids are the building units of proteins. Identification of amino acids is extremely important for the evaluation of protein structure and also for the determination of the presence of amino acids in various natural products. Several methods to determine amino acids in biological and pharmaceutical samples have been reported. Thin-layer chromatography (TLC) is one of the most widespread analytical techniques used in the separation and identification of amino acids because it is an inexpensive method and consume only small amounts of samples and solvents. Various stationary phases are available, although silica gel is used by far the most widely. There are also different mobile phases for chromatogram development. Thin-layer chromatography is widely used for the identification of amino acids by various spray reagents [1–22]. Among these, ninhydrin is the most popular because of its high sensitivity [23]. However, ninhydrin produces the same purple/violet color with most amino acids (only proline and hydroxyproline produce yellow color).