Increasing the specificity of the forensic luminol test for blood

Abstract

It is shown that the presumptive luminol chemiluminescence test for the presence of traces of blood can be made more determinative by measuring the peak emission wavelength of the luminol chemiluminescence. When sprayed onto a surface containing traces of human haemoglobin, a 1 g/L solution of aqueous luminol containing 7 g/L sodium perborate gives an emission peak at 455 +/- 2 nm, whereas the same mixture gives an emission peak at 430 +/- 3 nm when sprayed onto a surface containing traces of sodium hypochlorite (household bleach). This spectral difference can readily be determined using spectroscopic equipment that either scans the spectrum before significant luminescence decay occurs or corrects the spectrum for the effects of any decay. It was found that bovine haemoglobin and human haemoglobin showed no significant spectral differences.

A Comparison of Four Presumptive Tests for the Detection of Blood on Dark Materials

“…The reaction of luminol to bleach and cleaning products containing hypochlorite is well documented (6,(21)(22)(23)(24)(25). However, bleach has been observed to provide a more intense and brighter reaction to luminol than blood, and it is suggested that an experienced user of luminol could differentiate between the reactions of blood and bleach (26)(27)(28)(29).…”

A study of common interferences with the forensic luminol test for blood

“…In view of such problems, it is surprising that there are few quantitative studies of interferences with the luminol test that may occur in industrial and domestic situations. A recent paper (2) from the present research group has shown that sodium hypochlorite (a common component of domestic and industrial bleaches) produces substantial interference with the luminol test, as it catalyses* the formation of chemiluminescence which is easily as bright as that caused by haemoglobin. This is a particularly serious issue, as attempts to clean up a crime scene and remove a trace of blood may well involve the use of commercial and household bleaches.…”

“…The test involves spraying suspected blood samples with a standard mixture of luminol (5-amino-2,3-dihydro-1,4-phthalazinedione) dissolved in alkaline, aqueous solution containing either dilute hydrogen peroxide or sodium perborate (2). Traces of human blood as small as 1 ng can be detected (3) by the pale blue chemiluminescence emitted when they come into contact with the forensic luminol mixture.…”

Age determination of blood spots in forensic medicine by force spectroscopy

“…For the evaluation of suspected bloodstains solutions such as phenolphthalein, tetramethylbenzidine can be used, as they change color when they come into contact with peroxidase or hemoglobin in the blood [1]. For the detection of even minute amounts of blood traces the presumptive luminol chemiluminescence test is widely used in forensic practical work [2]. It is further possible to unambiguously attribute the blood to a certain individual by using molecular biological techniques, such as genetic fingerprinting [3].…”