Kaosium
Philosopher
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- Oct 12, 2010
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Maybe based on the literature that you have read in the last two days.
But there is literature about luminol being far more sensitive than TMB without ascorbic or citric acid or other equivalent reducents, and its being more specific. Reducents are very common on living organisms including human beings, since the body defends its tissues though anti-oxidizing agents; not to speak about that strong chemical reductant called THC (Cannabis) that Knox and Sollecito had assumed in significant amount that day. But his is irrelevant: researches found that luminol is just more sensitive than TMB and more specific, full stop.
There is for example - but it's just an example - this article:
S. Tobe; N. Watson; Nic Dae´id – “ Evaluation of Six Presumptive Tests for Blood, Their Specificity, Sensitivity, and Effect on High Molecular-Weight DNA” - (2007)
It is worth reading; I just quote a table about compared specificities of luminol (left) and TMB (right). NR = no reaction; in brackets the number of positive samples of a total of 25; out of brackets the number of minutes. Dilution is probably 1:10'000 but I'm not sure should read again for that figure.
The number of minutes within the reaction needs to be 1 or less for TMB to be declared a positive result. There is a list of substances reacting with luminol and TMB. In parentheses the number of positive results out of 25 samples. For example, tomato gave positive reaction to TMB on 23 samples out of 25; while luminol gave no reaction (“NR”). Red onion yielded 21 positive results to TMB.
Interestingly, chlorine was found non reactive to luminol. Authors assume this is because sample stains were all 18 hours "old". Sodium hypochlorite solution is believed to loose its property of triggering luminol reaction as the time passes due to evaporation.
I see you found Tobe et al again. Last time around I told you why Tobe didn't get reactions from materials you known damn well from other papers will get a false positive with luminol.
Tobe didn't cheat, but his findings puzzled even you--remember? The last paper sums it up pretty well near the end of page 5:
Webb et al. [22] conducted a study where the luminol test was compared to four other forensic blood tests. These tests where phenolphthalein, LMG, Hemastix (Bayer) and a forensic light source. The luminol test used was found to have by far the greatest sensitivity. Under laboratorial conditions CL was detected from luminol treated stains of the used hemoglobin solution (corresponding to blood) diluted up to 5·106 times. A comparably high sensitivity of the luminol test has been reported in other studies [22].
However the sensitivity is probably not as great under the conditions found at a crime scene and here, depending on several factors, perhaps one may “only” see blood diluted to about 1:10000 [14].
However the sensitivity is probably not as great under the conditions found at a crime scene and here, depending on several factors, perhaps one may “only” see blood diluted to about 1:10000 [14].
'Lab conditions' which allow for those ungody sensitivities include LI goggles to discern the reactions. If you look at the materials section in Tobe you won't find he used those goggles, just 'near or total darkness' as I believe he put it. If you go to the results section and look at his charts, as I recall you'll find he didn't show any greater sensitivity for luminol than he did TMB, they both bottomed out at about 10k:1. That's because he wasn't wearing the goggles and couldn't detect the reactions at lower levels--or with those items that give off weak CL glows with luminol. Thus luminol is only more specific employed like that because the reaction of those other items can't be detected...and neither can blood at those very diluted states. So it's actually not any more sensitive for blood than TMB under those conditions.