Phenophthalien Test: Investigating Blood Evidence in Bathtubs

[munky99999]

The Phenophthalien(i know i can't speel) test:

This one show they have a dead body, from the desert. They test a bathtub as they think the murder and blood was there. They use the pheno-blood test often.

But if its in the bathtub.

As pheno is just a ph indicator. Couldn't a base cleaner, as most are, change the readings, or make it look like there is blood where there isn't any?

Or is this just a fancy word that they are using for the fictional show and i am just being fanatical?

 

[chem_tr]

I am sorry but I could not understand your query fully. Are you asking this? "Can the presence of blood be determined with phenolphthalein, if the victim is in a bathtub?" Well, phenolphthalein may be a fluorescent material, and when mixed with a dried blood sample, it may cause the sample fluorescence; haemoglobin or other things in blood may combine with phenolphthalein to show a fluorescence. This is just a guess, though.

 

[Gokul43201]

I imagined that phenolphthalein was used as an indicator, since blood is mostly slightly basic.

However, it looks like the pH of human blood is only 7.35, whereas phenolphthalein only changes color at about pH 8. So, I'm not sure how well that would work.

But, as chem_tr said, it may be some fluorescent behavior that is important, rather than the pH. I think I recall seeing detectives (on TV) using a UV lamp to detect blood, but can't remember if the surfaces were treated prior to illumination.(excitation).

 

[iansmith]

Most of these tests rely on the activity of peroxidase enzymes in blood to react
with a chemical stain causing it to change color, or in the case of luminol, glow in the dark.

http://www.colorado.edu/Outreach/BSI/pdfs/for_bloodstud.pdf

 

[munky99999]

well i learned something, yaay.

 

[Moonbear]

I never expected such a thorough explanation from Court TV, but they've done a nice job of it http://www.crimelibrary.com/criminal_mind/forensics/serology/3.html?sect=21

The Kastle-Meyer Color Test uses a solution of phenolphthalein and hydrogen peroxide on a piece of filter paper, and when blood of any quantity is present, it turns pink.* However, it also turns pink in the presence of potatoes or horseradish, so care must be taken at the scene.