BLOCKING THE NINHYDRIN-SCHIFF REACTION WITH COPPER IONS.

THE ninhydrin–Schiff reaction of Yasuma and Ichikawa1 has been widely used as a histochemical method for the detection of α-amino-acids2,3 and recently it was applied quantitatively in cytochemistry by Rappay and Tork4. Whereas the detailed mechanism of the reaction has not been completely verified at the histochemical level, there is now fair agreement as to the specificity of the reaction for proteins5. The present experiments endeavour to show that colour production may be markedly affected by the purity of the reagents used.