Talanta 77 (2009) 1555–1557 Contents lists available at ScienceDirect Talanta journal homepage: www.elsevier.com/locate/talanta Short communication Bleach interference in forensic luminol tests on porous surfaces: More about the drying time effect Ana Castelló 1 , Francesc Francés 1 , Fernando Verdú ∗ University of Valencia EG, Facultad de Medicina, U. D. Medicina Legal, Av/Blasco Iba˜ nez n ◦ 15, 46010 Valencia, Spain article info Article history: Received 16 May 2008 Received in revised form 25 August 2008 Accepted 4 September 2008 Available online 13 September 2008 Keywords: Latent bloodstains Presumptive test Luminol Chemiluminescence Forensic science abstract As criminals try to avoid leaving clues at the scene of a crime, bloodstains are often washed away, but fortunately for investigators, they are difficult to eliminate completely. Porous surfaces easily retain blood traces, which are sometimes invisible to the naked eye. The reagent of choice for detecting latent blood traces on all types of surfaces is luminol, but its main disadvantage is a high degree of sensitivity to oxidising contaminants in the blood sample. If household bleach is used to clean bloodstains, presumptive tests are invalidated. Hypochlorites, however, are known to be unstable and deteriorate over time, and this feature could be of help in preventing household bleach-induced interference. Previous studies have evaluated the effect of the drying time on nonporous surfaces, but nothing has as yet been published about this effect on porous surfaces. Consequently, this paper reports on hypochlorite interference with luminol reagents used on this type of surface, evaluating the effects of drying time on the household bleach–luminol reaction, and ascertaining whether the drying procedure could be applied to prevent household bleach interference on bloodstained porous surfaces. The results indicate that the drying method may very well overcome household bleach interference in luminol reaction tests, if the investigation allows for an appropriate waiting time. © 2008 Elsevier B.V. All rights reserved. 1. Introduction As criminals will usually try to avoid leaving clues at the scene of a crime, bloodstains are often washed away. Fortunately for investigators attempting to find clues, bloodstains are difficult to eliminate completely. Porous surfaces easily retain blood traces, even if they are invisible to the naked eye. The mortar layers between bricks, porous bricks themselves, carpets and armchairs may retain latent blood traces that become visible when chemical reagents are applied during investigation. Luminol (3-aminophthalhydrazide) is currently considered to be an effective reagent for detecting latent blood. This compound has been known since 1853 [1,2], although it was only in 1937 when investigators proposed its use for detecting blood during criminal investigations [3,4,5]. It is considered to be a highly sensitive reagent, capable of detecting latent stains even when these are quite old, and useful ∗ Corresponding author. Tel.: +34 96864820; fax: +34 963864165. E-mail addresses: Ana.Castello@uv.es (A. Castelló), Francesc.Frances@uv.es (F. Francés), Fernando.Verdu@uv.es (F. Verdú). 1 Tel.: +34 963983774; fax: +34 963864165. for investigating large expanses of surfaces and helping to recon- struct the events that may have occurred at a crime scene [6]. It has also been shown that, following luminol treatment, DNA can be extracted and subsequently analysed using PCR [7,8]. Despite this, luminol cannot be considered a specific proof of blood detection. Studies on its selectivity show that, like other pre- sumptive reagents, luminol is sensitive to contaminating oxidising compounds which produce oxidation in the reagent (giving a pos- itive reaction) both in the presence and absence of blood, thereby giving rise to a non-specific reaction [9]. Consequently, the luminol reaction to contaminating oxidising agents is the main stumbling block when it is used to detect blood- stains. The author of a crime can easily prevent latent blood from being found by washing bloodstains with household bleach and water (or other household cleaning products with an oxidising capacity). The hypochlorites contained in household bleach react with luminol resulting in an invalid test, as the results of a luminol test performed on surfaces that have been washed with household bleach are unreliable. To solve this problem various solutions have been proposed: (a) an alternate formula for luminol, consisting of adding 1,2- diaminoethane. This amine reacts with the hypochlorites to prevent interference [10,11]; (b) other authors have shown that house- 0039-9140/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2008.09.008