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Phenolphthalein blood evidence tests

Crumbly Writer

I tried to locate this information online, and couldn't get a clear answer anywhere.

Phenolphthalein is mentioned as a simple chemical test for the presence of blood--not restricted to human blood. A couple questions:

1) Is this chemical widely used by the police to test for the presence of blood?
2) If so, does the typical police patrolman/officer in a car, have access to these tests (i.e. can they test a knife (for example) to tell whether it was potentially used in or crime) or
3) would it only be accessible by Detectives who are called in after the fact?

I've got an entire chapter resting on the results of this question. :)

Replies:   Dominions Son  REP  REP  bondsman
Dominions Son
Updated:

@Crumbly Writer


1) Is this chemical widely used by the police to test for the presence of blood?

2) If so, does the typical police patrolman/officer in a car, have access to these tests (i.e. can they test a knife (for example) to tell whether it was potentially used in or crime) or

3) would it only be accessible by Detectives who are called in after the fact?


It will vary a bit depending on the size of the force.

1. I think the use of alternative light sources is more common these days. It will detect all manner of bodily fluids in one pass. The chemical test are left for the crime lab.

2. No, a uniformed officer in a marked car would not likely carry such tests. Some might carry a small UV flashlight. These are available on the open market, not restricted to law enforcement.

3. A detective would not have the chemical tests, he will probably have a compact UV light source.

The various CSI shows get it half right. Most large PDs have specialized crime scene teams. These are science techs who process the scene for evidence.

What the CSI shows get wrong is that the crime scene techs are a completely separate group from the lab techs that process the evidence in the crime lab.

The crime lab processing also usually takes weeks or months.

REP

@Crumbly Writer

2) If so, does the typical police patrolman/officer in a car, have access to these tests (i.e. can they test a knife (for example) to tell whether it was potentially used in or crime) or

3) would it only be accessible by Detectives who are called in after the fact?


Logic would say No to both questions.

2) In general, a patrolman's job is to secure a crime scene not investigate it. However, in smaller police departments there may be no crime scene investigation group, so the patrolman may be called on to do limited investigation. However, such departments would probably call in county or state agencies to do the investigation.

When my brother worked patrol as a County Sheriff's Deputy, he was required to carry certain investigative equipment, so it would probably depend on department policy.

3) A Detective's job would require him to ensure evidence was collected by the appropriate people. They may be familiar with the techniques, but I doubt they are fully trained in the use of the techniques used to collect evidence. Once again, it would depend on local policy and capabilities.

REP

@Crumbly Writer

1) Is this chemical widely used by the police to test for the presence of blood?


It was my understanding that they used luminol. I don't know how luminol is produced, so Phenolphthalein may be used in luminol.

Dominions Son

@REP

It was my understanding that they used luminol. I don't know how luminol is produced, so Phenolphthalein may be used in luminol.


Field chemical tests for body fluids are falling by the wayside in favor of alternative light sources since most body fluids will fluoresce under UV light.

Crumbly Writer

@REP

It was my understanding that they used luminol. I don't know how luminol is produced, so Phenolphthalein may be used in luminol.

That's what I recall, but while searching, about all I could come up with were rudimentary chemical tests performed in high school labs. Phenolphthalein is a straightforward chemical test which turns different colors when exposed to different biological markers, while (I believe) luminol causes dried blood (and other fluids, like semen) to show up under UV light.

What I'm going for is: someone is seen waving a bloody knife, the police pounce, but then cannot find any evidence (with only a cursory view) of any blood.

The natural follow-up would be to pull out a quick test, but if there's no evidence of a crime, they couldn't send it to a lab for a followup investigation.

Replies:   Dominions Son  REP
Crumbly Writer

Nope. Luminol is a complete no-go. It's a liquid (either a spray or a dip, which also requires precise lighting (dark room in addition to a strong blue light, UV preferred). None of those things would a typical patrolman have on them.

Guess I'll have to drop the entire follow-up issue.

Dominions Son

@Crumbly Writer

while (I believe) luminol causes dried blood (and other fluids, like semen) to show up under UV light.


Luminol does not require UV light, only darkness as the light is generated by a chemical reaction.

Replies:   Dominions Son
REP

@Crumbly Writer

What I'm going for is: someone is seen waving a bloody knife, the police pounce, but then cannot find any evidence (with only a cursory view) of any blood.


The concept of a bloody knife that has no blood sounds like a flaw. Unless of course, you intended to have some other red substance on the knife that was misidentified as blood.

Dominions Son

@Dominions Son

http://www.crime-scene-investigator.net/alternatelightsources.html

Apparently I was wrong alternate light sources can't be used for blood.

Dominions Son

@REP

The concept of a bloody knife that has no blood sounds like a flaw. Unless of course, you intended to have some other red substance on the knife that was misidentified as blood.


No, wiping the blade off with a cloth would remove any naked eye traces of blood but unless chemical cleaners are used, there would still be enough blood on the blade to be detected by luminol.

Replies:   REP
REP

@Dominions Son

CW's description of his scene included the patrolman pulling out his test kit and testing for blood and finding none. It also suggested that the knife wielder did not have time to properly clean the knife of all traces of blood.

Replies:   Dominions Son
Lugh

Ninydrin perhaps, but phenolpthalein is principally an acid-base indicator. It's also the laxative in Ex-Lax.

Replies:   Ross at Play
Dominions Son
Updated:

@REP


It also suggested that the knife wielder did not have time to properly clean the knife of all traces of blood.


Visible blood would probably be enough for probable cause to seize the knife and arrest the wielder even without a specific field test, unless the knife wielder has a reasonable explanation for having a knife covered in blood (it's animal blood and he's a butcher, a hunter who just field dressed a kill, hey we're shooting a movie here, it's fake blood.)

That's why I was assuming that he had at least enough time to wipe it down with a rag and toss the rag (only take a couple of seconds) so that by the time the cops caught him there wasn't blood visible to the naked eye on the blade.

An experienced cop is not likely to be fooled by paint, or ketchup.

Replies:   Not_a_ID  Crumbly Writer
Not_a_ID
Updated:

@Dominions Son

The one problem with testing a knife for it having "encountered blood" is that unless that knife has been cleaned using atypical methods, it'll test positive months or even years later.

I remember that much from an investigative report by 48 hours, IIRC(its probably been close to 20 years since I saw this one). They went back to the suspects house, where they think the crime occured, based on new evidence, YEARS later(other people were living in it by then), and tested the garage floor. They found evidence that a rather large pool of blood had existed there at one point.

Edit to add: And considering they later discovered the suspect had bleached the area as part of his cleanup....

Yeah, seems to me that trying to remove all evidence of blood having been somewhere is like descenting somewhere an animal(or person) urinated at. The only way be sure is to outright replace the impacted area/items.

Dominions Son

@Not_a_ID

Edit to add: And considering they later discovered the suspect had bleached the area as part of his cleanup....


Bleach is pretty good. It will destroy any DNA, so they might be able to determine that there had been blood there, but they won't be able to prove who or what the blood came from.

Dominions Son

@Not_a_ID

The one problem with testing a knife for it having "encountered blood" is that unless that knife has been cleaned using atypical methods, it'll test positive months or even years later.


The important tests are not for detecting the presence of blood, but getting blood type / DNA information to determine what/who the blood came from.

Crumbly Writer
Updated:

@Dominions Son


Visible blood would probably be enough for probable cause to seize the knife and arrest the wielder even without a specific field test, unless the knife wielder has a reasonable explanation for having a knife covered in blood (it's animal blood and he's a butcher, a hunter who just field dressed a kill, hey we're shooting a movie here, it's fake blood.)


Don't forget, we're talking sci-fi here, so there are alternatives to their not finding evidence of the blood. But the whole point of the chapter rests of the cops having a ready access to the test while ON the street. If they have no direct evidence of blood (Hint: it wasn't wiped off), then they'd have no cause for seizing it for later testing.

Thus the whole exchange rests upon the cops having 1) access to the equipment and 2) being able to use it in bright sunlight on a busy street (I need a crowd for the scene).

As to why blood might disappear, I'll leave that to your imaginations, as often, these explanations often degrade into story spoilers.

Frankly, requiring UV light would be easy to incorporate, but requiring a dark room to observe the blue light wrecks the entire scene. :(

@Not_a_ID

The one problem with testing a knife for it having "encountered blood" is that unless that knife has been cleaned using atypical methods, it'll test positive months or even years later.


I know we're discussing 'traditional usage' here, but the point isn't what evidence could be used in a trial, but rather, given the complete lack of on-the-scene evidence, the cops would really have no justification to seize the weapon for later testing.

That's the fallacy of the entire scene, not the fact that someone quickly wiped the blade clean and there's some dead body lying there requiring a full forensic team and seasoned detectives.

P.S. I don't object to everyone discussing the use of luminol, but rather than continuing to discuss my story (and giving away vital story elements), I'd prefer moving the discussion to private emails. There are specific reasons for the 'lack of blood', but it's not open to discussion here.

Replies:   Dominions Son
Dominions Son

@Crumbly Writer

Don't forget, we're talking sci-fi here


This is the first you've mentioned that we're talking about sci-fi.

If they have no direct evidence of blood (Hint: it wasn't wiped off), then they'd have no cause for seizing it for later testing.


If they see a knife with what appears to be fresh blood on it visible to the naked eye, that would be cause enough to size it for later testing, at least under current US law. I pay attention to police issues, especially where it edges into official misconduct. Probable cause is a much weaker standard than most people realize.

I'm open to an email discussion. I'll let you make first contact.

Ross at Play

@Lugh

Ninydrin perhaps, but phenolpthalein is principally an acid-base indicator. It's also the laxative in Ex-Lax.

So the patrolman drops his pants, does a number two on the knife and sees if it glows?

sejintenej

@REP

The concept of a bloody knife that has no blood sounds like a flaw. Unless of course, you intended to have some other red substance on the knife that was misidentified as blood.

Looking at the books, if the knife had been cleaned with bleach there would still be the same (but slower) reaction. Cleaning a crime scene with bleach could cause a few problems for the police!

Incidentally, whilst Phenolphthalein is normally used in titration to identify the degree of acidity it SEEMS to be connected chemically with luminol

Replies:   Crumbly Writer  REP
remarcsd

The beverage industry uses phenolphthalene to test for residual caustic in pipelines after a caustic cleaning solution had been pumped through it. I never understood the confidence crime scene shows had in using it to prove the presence of blood.

Crumbly Writer

@sejintenej

Incidentally, whilst Phenolphthalein is normally used in titration to identify the degree of acidity it SEEMS to be connected chemically with luminol

I'm pretty sure it's one of the central components in luminol, as the side-effects (including the laxative effects) are identical in the two products (one natural, one produced in a factory).

@remarcsd

I never understood the confidence crime scene shows had in using it (phenolphthalene) to prove the presence of blood.

That's why they don't rely on it alone. It's mostly used for lab experiments in high-schools. It's got a high-rate of false positives, and all it detects is the presence of A blood substance, without the ability to distinguish between human, rat or pig's blood. Luminol is a better indicator, but it still needs to be followed up with a DNA analysis to determine who's blood it is. Even so, the police routine use it to argue guilt given a lack of other evidence when an area has been 'wiped clean' using bleach.

Replies:   REP
REP

@sejintenej

Looking at the books, if the knife had been cleaned


Not a complaint, but one of the problems I've noticed in the Forum is our discussions are rarely limited to the described scenario. In this case, CW did not define the knife as being wiped clean. A second problem is scenario descriptions that do not provide full disclosure of the scenario's details until we hypothesize what-if situations that do not conform to the actual scenario.

Replies:   Crumbly Writer
REP

@Crumbly Writer

I'm pretty sure it's one of the central components in luminol,


In researching Luminol I wanted to know if phenolphthalene was a component of luminol. The article gave a chemical breakdown. Not my area of expertise. If it is I didn't recognize it in the description.

Replies:   sejintenej
Crumbly Writer

@REP

Not a complaint, but one of the problems I've noticed in the Forum is our discussions are rarely limited to the described scenario. In this case, CW did not define the knife as being wiped clean. A second problem is scenario descriptions that do not provide full disclosure of the scenario's details until we hypothesize what-if situations that do not conform to the actual scenario.

That was a point I raised, as often, the 'requested context' requires a detailed explanation of the basic plot. Seeing as how the first draft isn't entirely written yet, I hate giving away plot details before they're even cemented yet.

For the described scene, there IS no bleach, no one wiped anything down, the blood simply Disappears with no chemical trace left whatsoever. However, that should sidetrack the larger discussion about how these products are used by police departments around the world. That's more apropos to most authors anyway.

bondsman

@Crumbly Writer

As I read the details of the scene you've provided; crowd of people, on the street, etc. Just the situation of someone waving a knife around, with or without blood, would be sufficient cause for arrest and seizure of the knife. (Note: I did not say it would lead to successful prosecution of the individual.) That's unless you've built a rather unusual legal system into the story. The exact charge would vary from state to state and perhaps city to city but it would likely boil down to endangering the public.

Replies:   Crumbly Writer
Crumbly Writer

@bondsman

As I read the details of the scene you've provided; crowd of people, on the street, etc. Just the situation of someone waving a knife around, with or without blood, would be sufficient cause for arrest and seizure of the knife. (Note: I did not say it would lead to successful prosecution of the individual.) That's unless you've built a rather unusual legal system into the story.

Ha-ha. Yeah, normally that's the case. However, if you want to see how the MC works around the issue, you'll eventually have to read the story! :)

sejintenej

@REP

In researching Luminol I wanted to know if phenolphthalene was a component of luminol. The article gave a chemical breakdown. Not my area of expertise. If it is I didn't recognize it in the description

The correct technical name of luminol is
5-Amino-2,3-dihydrophthalazine-1,4-dione

The manufacturing process does not include phenolphthalene, hence my caution about a direct connection

Replies:   REP
REP

@sejintenej

I know that was why did not to say it definitely did or did not contain the chemical.

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