When performing a thin layer chromatography analysis of an aqueous plant extract, violet spots corresponding to the amino acid standards used to study their presence appeared, and very faint blue spots appeared in place of the samples after using ninhydrin reagent. These faint blue spots do not correspond to any of the more than 20 amino acid standards used as they showed defined spots of intense violet color. What interference in the sample could have caused these faint blue spots when reacting with ninhydrin?
A solvent system of Chloroform: methanol: 25% ammonia (40:40:20) was used and the blue spots presented an Rf (0.57).
Not my field but I suggest that you search for 'specificity' of the reaction in Google/Google Scholar
Ninhydrin can also react with primary amines to give the purple color and also with secondary amines to give a less intense coloration.
It can be all kind of peptides that are also present in such extracts. When you used traditional extraction with heat application, then also smaller lipophilic reaction products from the Maillard reaction would be present as well.
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