Performance of 1,2-indanedione and the need for sequential treatment of fingerprints

The use of 1,2-indanedione-ZnCl2 (IND-Zn) for the visualisation of fingermarks on porous materials has been widely accepted. The use of the reagent in comparison with others has been well described. To what extent IND or IND-Zn reacts with amino acids, in comparison to ninhydrin, has not been described to date. In this technical note we describe the analysis of amino acids with LCMS with the purpose of understanding the reactivity of ninhydrin, IND-Zn and the sequence thereof. The consumption of amino acids by these visualisation reagents is a feature we propose to use for calculations on the reactivity of these reagents. By using recently developed methods for the quantification of amino acids, we determined the consumption of these entities by visualisation reagents. We show that the differences in reactivity between IND and ninhydrin are not as big as the differences between 1,8-diazafluoren-9-one (DFO) and ninhydrin. We also show that it is of great importance to use IND-Zn and ninhydrin in sequence, in order to fully consume the amino acids present in fingermarks.