Amino acid sensitive latent fingermark detection formulations based upon improvised carrier solvents for resource-limited environments: A proof-of-concept study

HFE-7100 and petroleum ether (bp 40–60 °C) are routine carrier solvents used in amino acid sensitive fingermark reagents such as 1,2-indanedione/zinc chloride (IND-Zn) and ninhydrin. However, limited resource jurisdictions face major challenges in sourcing laboratory-grade reagents due to budgetary and geographical restrictions. Common hydrocarbon solvents, available from hardware stores and similar outlets, may offer a more readily available and inexpensive alternative for such jurisdictions. This study assessed the range of improvised carrier solvents for their suitability in the IND-Zn formulation and found that eight different hydrocarbon solvents were able to develop fingermarks when substituted into the formulation. The formulation based on shellite solvent outperformed all other improvised formulations tested, providing high-quality fingermarks and similar sensitivity to a petroleum ether (bp 40–60 °C) based formulation across six porous substrates using six donors. A similar approach was applied to ninhydrin, where it was discovered that formulations using kerosene, white spirits and shellite as carrier solvents performed comparably to a formulation based on petroleum ether (bp 40–60 °C). By chemically characterising each solvent using gas chromatography-mass spectrometry, this study also provided a greater understanding of how the chemical composition of a carrier solvent impacts the efficacy of the resulting IND-Zn formulation, emphasising that hydrocarbon solvents should contain short-chain alkanes and minimal aromatic content to give a more volatile formulation. Additionally, the identity of the solvent was found to cause slight differences in the colour and luminescence intensity of ink diffusion on porous substrates. These results indicate that improvised hydrocarbon solvents are suitable alternatives to common carrier solvents with their operational use offering major benefits for limited resource jurisdictions by reducing costs and supply chain risks. A thorough risk assessment must be conducted by each jurisdiction that intends to use this method as health and safety considerations are concerns with these improvised solvents.