Use of benzalkonium chloride and cetyltrimethylammonium bromide for post-treatment of ninhydrin developed fingermarks on A4 papers

Abstract

Previous studies have shown that the cationic surfactants benzalkonium chloride (BAC) and cetyltrimethylammonium bromide (CTAB) enhance the visualization of ninhydrin-amino acid compounds (Ruhemann’s purple). However, applying BAC or CTAB directly to fingermarks composed of amino acids, after development with amino acid sensitive reagents has not been investigated. Therefore, the authors studied whether the development of fingermarks left on paper with amino acid sensitive reagents and the subsequent post-treatment with cationic surfactants would result in further enhancement. First, the purple compound obtained by treating the amino acids contained in a spot with ninhydrin turned blue when post-treated with BAC or CTAB, indicating that BAC or CTAB has the potential to darken the color of ninhydrin-developed fingermarks and make it more visible. But when fingermarks on paper were developed with ninhydrin and then post-treated with BAC or CTAB, the color of the fingermarks shifted from purple to blue, but the overall sensitivity was similar to fingermarks without BAC or CTAB. Furthermore, no significant effect was observed when fingermarks develop ed with 1,8 - diazafluoren - 9 - one o r 1,2 - indanedione/zinc instead of ninhydrin were treated with BAC or CTAB. However, further testing on colored papers showed that adding BAC or CTAB to ninhydrindeveloped fingermarks may provide better contrast on red-based papers.