Automatic Flow System for Sequential Detection of Zinc and Acid Phosphatase in Forensic Samples

Abstract

Body fluid identification is an important step in criminal investigations, especially in cases of sexual crimes, which have a high global incidence. According to the World Health Organization (WHO), it is estimated that one in three women worldwide has experienced physical and/or sexual violence. In this context, to confirm rape, biological samples, such as semen found at the crime scene or on the victim, are collected. To overcome the limitations of conventional tests, this study employed a Sequential Injection Analysis (SIA) system for simultaneous spectrophotometric detection of acid phosphatase (AP) and zinc ions, markers present in semen at elevated concentrations. Under optimized conditions, the system showed a detection limit of 9.4 U L⁻¹ for AP and 3.1 μM for Zn(II), with limits of detection below 2.8% and recoveries ranging from 91.0 to 105.5%. The method's selectivity was evaluated using different biological samples (semen, saliva, urine, and blood serum). Among these, only the semen sample displayed significant signals for both markers. Therefore, the developed SIA system enables qualitative and quantitative analyses with a reduced sample volume; additionally, it is a greener method than batch studies. Overall, it is a potentially valuable tool in the elucidation of sexual crimes.

Keywords: forensic application, colorimetric detection, markers, semen, zinc, acid phosphatase