Fingermark visualisation with iron oxide powder suspension: The variable effectiveness of iron (II/III) oxide powders, and Tween® 20 as an alternative to Triton™ X-100

Abstract

The effectiveness of the current UK iron oxide powder suspension formulation, ‘C-IOPS-09’ (Triton X-100 based), for fingermark or latent fingerprint visualization is shown to be affected by variations between batches of the recommended iron oxide powder from Fisher Scientific (I/1100/53). When incorporated into the C-IOPS-09 formulation, a 2015 powder batch resulted in the detection of ∼19% fewer fingermarks, of broadly reduced contrast, when compared to powder suspension prepared with a 2008 batch of the same product. Furthermore, the 2015 powder batch was found to be unsuitable in experimental reduced-surfactant concentration powder suspension, because it caused surface-wide or background staining. The studies in this paper also investigated the use of Tween 20 surfactant as an alternative to the currently utilised Triton X-100, in preparation for the potential unavailability of Triton X-100 in the future. Powder suspensions prepared with Tween 20 surfactant solutions of 4% and 40% were shown to offer similar effectiveness to the currently recommended C-IOPS-09 formulation, when compared using the same batch of Fisher Scientific iron oxide powder (2008 or 2015). The difference between the 2008 and 2015 iron oxide batches was hence also evident with these alternative surfactant solutions. Particle size distribution analysis of the iron oxide powders in Tween 20 and Triton X-100 based surfactant solutions show that the more effective powder exhibits a higher sub-micrometre particle population than the less effective powder. This work leads to an improved specification for powder suspension formulations. This is demonstrated with an example powder suspension formulation which uses a 10% Tween 20 surfactant solution and iron oxide nanopowder (50–100nm) from Sigma Aldrich, which was shown to visualise 27% more fingermarks than the C-IOPS-09 formulation prepared with the 2015 Fisher Scientific powder batch, in a comparative study.