The Naked Scientists

The Naked Scientists Forum

Author Topic: How do detectives detect blood?  (Read 1997 times)

Offline colarris

  • Full Member
  • ***
  • Posts: 54
    • View Profile
How do detectives detect blood?
« on: 23/02/2010 21:45:21 »
  What is the liquid you see the people in these CSI shows use to detect whether a substance is blood or not?
« Last Edit: 04/08/2011 16:40:00 by BenV »


 

Offline RD

  • Neilep Level Member
  • ******
  • Posts: 8126
  • Thanked: 53 times
    • View Profile
Re: How do detectives detect blood?
« Reply #1 on: 23/02/2010 21:57:16 »
Quote
Phenolphthalein is used to perform a presumptive blood test, and is commonly known as the Kastle-Meyer test. A dry sample is collected with a swab or filter paper. First a few drops of alcohol, then a few drops of phenolphthalein and finally a few drops of hydrogen peroxide are dripped onto the sample. If the sample turns pink then it is a positive test. This test is nondestructive to the sample; it can be kept and used in further tests at the lab. This test has the same reaction with blood from any animal, so further testing would be required to determine whether it originates from a human.
http://en.wikipedia.org/wiki/Phenolphthalein#Uses

« Last Edit: 23/02/2010 22:01:27 by RD »
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8660
  • Thanked: 42 times
    • View Profile
Re: How do detectives detect blood?
« Reply #2 on: 23/02/2010 22:01:50 »
phenolphthalin

(And that's the right spelling; I don't mean the relate chemical phenolphthalein)
http://www.fbi.gov/hq/lab/fsc/backissu/oct2004/technote/2004_10_note01.htm
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8660
  • Thanked: 42 times
    • View Profile
Re: How do detectives detect blood?
« Reply #3 on: 24/02/2010 19:59:46 »
The red colour developed in the test isn't due to haemoglobin.
You could use thymolphthalin and it would turn blue (even if the blood weren't royal).
 

The Naked Scientists Forum

Re: How do detectives detect blood?
« Reply #3 on: 24/02/2010 19:59:46 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums