Further research into alternative carrier solvents for the detection of latent fingermarks.

A number of solvents, (Solstice PF, Opteon SF33 and Amolea AS-300), are compared to the recommended carrier solvent of HFE7100 for the ninhydrin and 1,2-indandione formulations. As the supply of HFE7100 will cease by the end of 2025, suitable alternatives are required in the short-term to ensure the detection of latent fingermarks on porous surfaces is still effective. Although these solvents, with the exception of Amolea AS-300, are classified as per- and polyfluoroalkyl substances (PFAS); they are not classed as hazardous. The alternatives in this study have a low global warming potential and atmospheric lifetime and are volatile, non-flammable and non-ozone depleting, in addition to other desirable properties such as a high wetting-index. During Phase 2 trials with deposited fingermarks, HFE7100 provided the best performing results followed by Opteon SF33, Solstice PF and Amolea AS-300. A significant difference with a negligible effect size was observed for ninhydrin formulations (p-value 0.00179; ε2 0.00418) while a significant difference with a weak effect size was observed for 1,2-indanedione formulations (p-value 2.095 ×10-10; ε2 0.0167). Furthermore, HFE7100 provided the least ink diffusion and the brightest 1,2-indanedione luminosity (significant difference with a moderate effect size p-value 1.772 ×10-13; ε2 0.0434) but the HFE formulation turned cloudy more quickly and needed regular replacements. Phase 3 pseudo-operational trials of 100 porous items followed a similar trend whereby HFE7100 formulations detected the highest number of marks followed by Opteon SF33 and Solstice PF. Although HFE7100 is still the best performing carrier solvent, this study demonstrates that, in the short-term, Opteon SF33 and Solstice PF may have potential as non-flammable replacement carrier solvents while developing the long-term goal of solvent-less methods.

Modelling the Condensation Process of Low-Pressure Refrigerants in Mini-Channels.

The measure of the energy efficiency of the non-adiabatic two-phase condensation process of refrigerants in mini-channels is both the value of the heat transfer coefficient α and the flow resistance expressing the external energy input required to realize the flow. The modelling of this very complex process is effective if the condensation mechanism in mini-channels is correctly identified. It has been proven that the effects of changes in the condensation mechanism are the different structures of the two-phase flow resulting from process interactions both in the channel cross-section and along the flow path. The research aimed to connect the value of the heat transfer coefficient with the flow structures occurring during condensation. Thermal and visualization studies of the condensation process of low-pressure refrigerants were carried out: Novec649, HFE7100 and HFE7000 in tubular mini-channels with diameters dh = 0.5; 0.8; 1.2; 2.0 mm. Based on visualization studies, flow structures were proposed to be divided into 3 main groups: dispersive, stratified and intermittent. Based on this, a computational correlation was derived for determining the heat transfer coefficient and frictional resistance depending on the type of flow structure. The research shows that the highest values of the heat transfer coefficient occur during the mist flow and the lowest during the bubble flow.

Effect of carrier solvent in 1,2-indanedione formulation on the development of fingermarks on porous substrates.

As an important technique for the detection of fingermarks on porous surfaces, 1,2-indanedione is widely used due to its excellent detection performance. In order to optimize the effectiveness of 1,2-indanedione, several institutions have modified the original formulation. In this study, four different 1,2-indanedione formulations were used to treat fingermarks deposited on different porous substrates to determine the most suitable formulation and whether Solstice-PF can be an alternative carrier solvent for the currently used HFE7100. It was found that the Solstice-PF-based formulation performed similarly to the HFE7100-based formulation on copy paper, but when treating fingermarks deposited on brown paper and newspaper, Solstice-PF was superior to HFE7100 by developing up to 10% more marks graded 3 and 4 regardless of the ageing period. The results confirm that Solstice-PF can be used as an alternative carrier solvent for 1,2-indanedione formulations with good detection rates and lower costs.

An alternative carrier solvent for fingermark enhancement reagents.

Solstice® Performance Fluid (PF), trans-1-chloro-3,3,3-trifluoropropene, is presented as an alternative to HFE7100, methoxy-nonafluorobutane, as a carrier solvent in a number of chemical formulations used for the visualisation of latent fingermarks. The supply of HFE7100 may be at risk due to a recent European Union regulation to control global warming. Laboratory trials using split depletions and a pseudo-operational trial of 1000 porous samples have shown that Solstice® PF is a viable alternative to HFE7100 for the chemical formulations of ninhydrin and 1,2-indanedione. Other preliminary trials have also indicated that Solstice® PF can be used as a carrier solvent for the zinc toning of marks found using ninhydrin as well as the α-naphtholflavone fixative solution for iodine developed marks. Results from the pseudo-operational trial demonstrate that the number of marks detected by ninhydrin and 1,2-indanedione formulations for each carrier solvent is comparable. When compared to HFE7100, advantages of Solstice® PF include a very low global warming potential and atmospheric lifetime in addition to a higher wetting index and lower costs. This study also provides a validation study that supports the potential replacement of DFO with 1,2-indanedione.

Development of fingermarks on Latex gloves: The solution to a challenging surface.

Used Latex gloves found at crime scenes can provide strong evidence against a suspect as they almost certainly contain both the fingermarks and DNA of the perpetrator who had worn them. However, over the years, Latex gloves have proved to be a rather difficult substrate for fingermarks development, with most of the standard techniques producing poor results. In this study, the two main protocols for development on either porous or non-porous surfaces: Ninhydrin-HFE and superglue fuming followed by crystal violet (CV) dyeing, respectively, had been examined on 100 disposable Latex gloves from twenty five donors. The results distinctly showed a high superiority of Ninhydrin-HFE over the superglue fuming indicating the porous rather than the non-porous properties of the interior of the gloves. Yet, not all the usual ninhydrin development formulations yielded the desirable results, leading to the conclusion that the success of development rests on the solvent-sensitive structure of the gloves. As natural latex contains contaminant proteins, that were found to cause allergic reactions in different people, the manufacturing of disposable gloves had been altered over the years to prevent contact with these proteins by adding an intrinsic polymer-coating. Thus, it was essential to use an inert solvent system that should keep the interior polymer-coating intact, allowing a reaction only with the amino acids on the surface rather than the latex proteins in the glove. The SEM analyses showed that HFE-7100 as opposed to petroleum ether, does not harm the inner coating, hence, providing the ideal solution to this challenging surface.