Ascorbic acid: an unstable ninhydrin-positive urinary constituent running with valine in a commonly used screening system.

Large amounts of ascorbic acid occur occasionally in the urine of children being investigated for possible inherited metabolic disease and may give a positive ninhydrin reaction after thin-layer chromatography. As this compound is unstable in urine and runs with valine in a solvent system commonly used for preliminary screening, it is a possible source of confusion.