Presumptive tests: A substitute for Benzidine in blood samples recognition

Abstract The nature of the sample in a forensic case is one of the most important factors, since it determines the posterior analysis, helping to define or discard its identity (like blood versus semen). A presumptive test is a qualitative analysis that allows to identify, or confirm, the presence of a substance in a sample. These determinations usually occur, after a chemical reaction, and a specific colour is produced. A false positive is another substance reacting the same way, producing the expected result. The aim of this work was to evaluate the most effective presumptive test (with fewer false-positives) when analysing products that could look and behave like blood during a forensic screening assay. Eight different products were tested, like Betadine ® , and four reagents were considered: Tetramethylbenzidine, O-toluidine, Leuchomalachite green and BlueStar ® Forensic (BlueStar). Each product was tested with the reagents five times − mixed with human blood (3:1), with three different animal blood (3:1), and then unmixed. Our results indicated that Leuchomalachite green is the most suitable presumptive test, since it was the reagent with less false positives.