To all,
I found some quotes in Barni et al., Talanta 72 (2007) 896–913. This paper is linked at the Friends of Amanda web site, and I have discussed it previously.
“The most problematic chemicals for a correct interpretation of luminol test results are those which provoke intensification or a generation of a chemiluminescence emission even if blood is not present, leading to false-positive results. Due to the possible presence of these substances at the crime scene, the luminol test must not be considered sufficiently specific to permit an unequivocal identification of blood [15,18,51,88,89].
Those compounds which generate luminol chemiluminescence, or enhance the luminol emission in the presence of bloodstains can be divide into three major categories (Fig. 13):
1. compounds showing a catalytic true peroxidase or peroxidase-like activity;
2. compounds with a high oxidizing capacity towards luminol;
3. compounds with a complex chemical composition with an undefined action mechanism towards luminol mixture.
The first group encompasses inorganic or bioinorganic species and undoubtedly is the major source of luminol interferences as these compounds often show excellent catalyzing properties in redox reactions such as that involving luminol oxidation and are widely distributed in the environment and in plants. In general three main types may be characterized in this group: free metal ions, in most cases included in inorganic compounds such as rust or soils; biological complexes between metal ions and organic components (such as metal–porphyrins, and including bacterial or plant pigments) often within protein structures; enzymes belonging to the oxidoreductases class such as horseradish-peroxidases.” (emphasis added)
SNIP
“Generally visual examination is used when the luminol test is employed in a forensic situation, rather than instrumental detection of the luminescence. An experienced practitioner may
distinguish the true blood-catalyzed chemiluminescence from that produced by other substances by the evaluation of parameters observable to the naked eye such as emission intensity,
duration and spatial distribution. However this approach may also lead to misinterpretation, due to a subjective, informal and non-quantitative evaluation, for example, because its intensity is
qualitatively much weaker than that expected for blood. In other circumstances an emission of similar intensity may be thought to derive from diluted bloodstains and is accepted. Therefore,
caution should be exercised when using the test. Any confusion which may arise over a stain can usually be resolved by an intelligent observation and, if necessary, by further testing [73], for example, by using a different presumptive test for blood, such as the immunochromatographic test for the confirmation of human blood presence Hexagon OBTI (Human GmbH, Wiesbaden, Germany) [137].”
I doubt presumptivity is a word (yet), but perhaps Lewis Carroll would be amused. It is intended to differentiate between whether a test is presumptive or conclusive.
