July 08, 2020, 07:17:06 AM
Forum Rules: Read This Before Posting


Topic: Chemical Forensics Questions  (Read 16781 times)

0 Members and 1 Guest are viewing this topic.

Offline forensicsresearcher

  • New Member
  • **
  • Posts: 4
  • Mole Snacks: +0/-0
Chemical Forensics Questions
« on: June 20, 2011, 03:31:19 AM »
Hello -- I'm a writer with a couple forensics questions. Sorry if these sound a bit macabre, but it's purely for fiction purposes, I swear.

1) Is there any way to detect blood with household chemicals? I know that crime scenes use luminol or phenolphthalein, but -- as far as I know -- there's no moderately easy way to mix up a homemade batch of anything comparable. Preferably, I'd like a way for a forensically knowledgable protagonist to detect traces of blood that have been wiped away from a surface without the help of a blacklight. Any way to do this? Any easy substitute for phenolphthalein?

2) Somewhat related to question one, I read somewhere that if you put a cloth that has a blood stain on it into a glass of hydrogen peroxide that the hydrogen peroxide would start bubbling because iron in the red blood cells catalyze the decomposition. Would this work if the blood stain were on a piece of wood, or metal, or some material other than cloth?

3) Do recently deceased corpses give off heat before they cool down? If so, how much? If a person died outside in the winter, would it be enough to melt some of the snow around them?

4) Does any scientific story or neat trick come to mind of how chemistry has been (or could be) used to gather criminal evidence? For example, I've read that the younger a person is, the faster their hair dissolves in lye (could be useful in solving a mystery case).

Thanks, looking forward to some interesting answers.

Offline AWK

  • Retired Staff
  • Sr. Member
  • *
  • Posts: 7390
  • Mole Snacks: +516/-86
  • Gender: Male
AWK

Offline rjb

  • Regular Member
  • ***
  • Posts: 65
  • Mole Snacks: +8/-0
Re: Chemical Forensics Questions
« Reply #2 on: June 20, 2011, 06:03:50 AM »
Hello,

In answer to your questions...

1) Sadly not! The two most commonly used presumptive tests for blood in the UK are Kastle-Mayer (a reduced form of phenolphtalein) and Leucomalachite Green (a reduced form of malachite green indicator). Both can be made relatively simply (if you can do a simple reflux and have access to zinc, acetic acid and potassium hydroxide), but you can get hold of either (without resorting to 'homebrewing') from any Crime scene company in the UK and USA whether you're in the business or not! Neither require a 'blacklight' as both give distinct colour changes, but will both react with many non-blood substances (Fresh horseradish is always the classicly demonstrated example) which can always add a nice twist to a plot line perhaps. Same deal with Luminol (also sold as a variant called 'BlueStar'), which contrary to Dexter and other forensic related TV programmes does not require a 'blacklight' for visualisation... I suspect that your forensically aware protagonist would have the sense to buy his presumptive test kits rather than make his own from household chemicals in an 'A' team style!

The following link may be of interest
http://www.nfstc.org/pdi/Subject02/pdi_s02_m02_02_a.htm

2) That is true and is in fact the basis of the tests described above, all of which include addition of hydrogen peroxide as a final step. The blood (through a surprisingly complex reaction) causes hydrogen peroxide to decompose oxidising KM, LMG or luminol to their coloured or luminiscent forms... One point to make is that the blood stain is rarely directly tested, a small spot is normally transferred to a filter paper and this is itself subjected to KM or LMG testing as immersing the original stain in testing reagent could compromise downstream analysis... Although you could in theory dump an item in hydrogen peroxide and observe efferevescence I suspect it would be a pretty poor method for detecting blood especially at low concentration.

3) I don't profess to be any kind of expert in this area but from what I am aware body cooling follows a sigmoidal curve, with the initial lag phase being due to residual anaerobic respiration which probably lasts from about 30mins to 3hrs at typical ambient. Following this is the typical 'newtonian' cooling... How this would all figure with a hypothermic individual is quite a complex question and depends upon a load of factors. Would some of the snow melt? Probably!

4) I shall give this one some thought and get back to you!

Good luck with the writing and I hoped this helped a bit...

R


Offline forensicsresearcher

  • New Member
  • **
  • Posts: 4
  • Mole Snacks: +0/-0
Re: Chemical Forensics Questions
« Reply #3 on: June 20, 2011, 01:43:28 PM »
Thanks! That's very helpful, just a few more questions now...

You said "[Kastle-Meyer and LMG] can be made relatively simply (if you can do a simple reflux and have access to zinc, acetic acid and potassium hydroxide)". How would I do this? The only chemistry I ever learned was simple high school stuff years ago, so I'm pretty dumb when it comes to science. The idea is that my character finds themself in a situation where they don't have access to their presumptive tests and would have to use household items instead. Are there common items with zinc, acetic acid, and potassium hydroxide that could be mixed to create a makeshift blood indicator? For interest's sake, I found this video on how to make luminol with household items: http://www.youtube.com/watch?v=lB_g2ddZZYk&feature=channel_video_title. A little too time consuming and complicated, though!

Also, I found out that phenolphtalein used to be used in laxatives, but has since been banned because it's carcinogenic. Say a peson found an old laxative pill that had it, though -- would the following instructions I found online work to turn it into a blood indicator?
1. Smash the tablets while wrapped in wax paper.
2. Add 30 mL of 2-propanol (rubbing alcohol) to the jar.
3. Add the powdered tablets to the jar and stir (may not fully dissolve).
4. Prepare aqueous solutions of household products.
5. Add 2-3 drops of the phenolphthalein indicator until colour change occurs (if the pH of the solution is below about 8, colour change will not occur).

Edit: Someone else told me that in order for the hydrogen peroxide test to work (described in my original post in question 2), the blood would have to be relatively fresh because catalese in blood breaks down relatively quickly. Is this true? Do the other tests require fresh blood or would dried blood be fine too?

Offline rjb

  • Regular Member
  • ***
  • Posts: 65
  • Mole Snacks: +8/-0
Re: Chemical Forensics Questions
« Reply #4 on: June 20, 2011, 05:06:26 PM »
My pleasure...

The following is the protocol I use for KM

http://static.dna.gov/lab-manual/Linked%20Documents/Protocols/pdi_lab_pro_2.15.pdf

If I were to make it at home (and I didn't have access to the required reagents), I would get hold of Phenolphthalein from a school, university or buy from ebay... Potassium Hydroxide from from a fine art photography shop of the type you only find in the pretentious parts of London (alternatively you could probably replace with Sodium Hydroxide (Lye)). Zinc from, well... have a look at the following link, some interesting ideas! 
 
http://www.hyperdeath.co.uk/chemicals/inorganic.php
http://www.hyperdeath.co.uk/chemicals/

The following is the recipe I use for LMG

http://static.dna.gov/lab-manual/Linked%20Documents/Protocols/pdi_lab_pro_2.18.pdf

Interestingly, last time I made up LMG, it didn't even need refluxing!
If I were to make it at home, I would buy malachite green online or from an aquarium shop, acetic acid could be distilled from vinegar I suspect and Zinc you already know!

As far as your recipe is concerned, assuming that your tablets did actually contain phenolphthalein in the first place (which is unlikely), I would use ethanol rather than propanol to extract the PP. This would then need to undergo the process described at the top of the page before it could be used as anything other than a pH indicator.

Regarding you last point, this is an interesting question... Catalase is present in liver at relatively high levels, but levels in blood (as far as I know) are nowhere near as high... What's actually causing the presumptive tests to do their thing is the Haem (heme if you live in the USA) complex and not catalase or peroxidases. From experience, presumptive tests work just as well on aged blood as they do on fresh blood. Even spot several year old will give a lovely pink or blue green KM or LMG response...

Hope this helps...

R


Offline forensicsresearcher

  • New Member
  • **
  • Posts: 4
  • Mole Snacks: +0/-0
Re: Chemical Forensics Questions
« Reply #5 on: June 20, 2011, 06:10:30 PM »
Again, extremely helpful! I hadn't really heard of LMG before this thread, but now I think it just might be the solution I'm looking for.

Regarding the catalese/peroxide question, here's what the other person told me: "Peroxide fizzes in the presence of blood because of an enzyme called catalase that breaks the H2O2 down into H2O and oxygen free radicals, which rapidly bond with another oxygen to form O2 that creates the bubbles. Dried blood won't fizz because the catalase breaks down fairly rapidly, I'm not sure of the half-life off the top of my head but unless the blood is fairly fresh I don't think you would get bubbles." Do you think he's right or wrong?

In any case, the peroxide, KM, and LMG methods are useful for determining if a stain or substance is potentially blood. Now a couple trickier questions...

1) Is there any homemade way to determine if two blood samples came from the same person? What if you knew one of the person's blood types? For example, Smith gets stabbed (Smith knows that his blood type is O+) and a cop finds a guy three blocks away with fresh blood on his shirt. Could the cop test the blood on the criminal to know if it is or isn't O+?

2) Back to blood that's been washed away from a surface. My character doesn't have luminol, but what if they used clear adhesive tape to remove any unseen blood cells from the surface and then examined the tape under a microscope. Would the blood cells show up?

3) On an un-blood-related topic, is there any way to make a homemade plaster substance that could be used for casting footprints from snow? I read that paste, wet breadcrumbs, and porridge can be used in an emergency; would this work?

Again, thanks for fielding my morbid questions!

Offline fledarmus

  • Chemist
  • Sr. Member
  • *
  • Posts: 1676
  • Mole Snacks: +203/-28
Re: Chemical Forensics Questions
« Reply #6 on: June 21, 2011, 07:29:55 AM »
A couple of suggestions:

For zinc, many boats have a chunk of zinc attached to the propellor shaft. This is a sacrificial anode, and it acts by corroding faster than the metal you want to protect. See http://en.wikipedia.org/wiki/Sacrificial_anode

For molding footprints, how about gelatin? Or a cooked mixture of egg-white and sugar, the type used for the hard-shell meringue cookies? Or for that matter, just plain sugar cooked to the hard-ball stage? Although the latter two might be too hot to get an impression from snow. You could also make a form of papier-mache from white glue and shredded paper that might be thin enough to pour into a footprint. Or if there is a workshop in the house, a spray foam insulation like Great Stuff http://greatstuff.dow.com/ might be perfect - goes in soft and fast, expands to fill the space, and dries hard.

Offline rjb

  • Regular Member
  • ***
  • Posts: 65
  • Mole Snacks: +8/-0
Re: Chemical Forensics Questions
« Reply #7 on: June 21, 2011, 12:21:13 PM »
Forensic Researcher,

Your other contributor is correct, catalase along with a variety of other peroxidases and inorganic catalysts breaks down hydrogen peroxide to water and oxygen. If the catalase concentration in blood is sufficient, I suspect addition to H2O2 would cause effervescence, but at the sorts of dilutions and volumes encountered at crime scenes the breakdown would not be visible as distinct from that which occurs naturally... H2O2 breaks down all by itself! Not a method that is is remotely useable... Additionally, nobody in their right mind would immerse an item of evidential value in H2O2! 
 
You might find the following interesting if you can access it via science direct... Forensic Science International. Volume 188, Issues 1-3, 1 July 2009, Pages 1-17

1) Sadly no... Unless your hero has a shed full of rabbits producing Anti-A and B immunoglobulins all day and if he has, someone surely must have rung up the RSPCA (or whatever the US animal cruelty equivalent is) by now! Test cards however can be readily bought or probably 'borrowed' from hospitals, surgeries; however, my view is that it would be best to avoid blood grouping altogether... The method is astonishly poorly descriminating, especially given that there are around 114 Million O+ individuals in the US alone!

2) I suspect that this technique may possibly work... The problem you have is that red blood corpuscles probably don't remain intact all that long. I also wonder if sticky tape would be an appropriate lifting medium. Other obvious point (as with all presumptive tests) is that you could well be looking at non-human blood... 

3) Dental Stone is the industry standard for forensic casting with good reason. I see no real point in using wet breadcrumbs, porridge etc. as you'll end up with (at best) a vague outline of a footwear mark with none of the fine detail necessary to descriminate between shoes of the same class, which is the whole point of the process in the first place! Why not take an image? Dentstone in your only real choice except in snow when (if you don't use snowprint wax first) the heat of the reaction melts your impression! Alternatives that have been used with limited success are: molten Sulphur (Marks in snow) and Molten paraffin wax (Marks in snow), but these are pretty crappy and are prone to bubbles.

Kind Regards

R

 

Offline forensicsresearcher

  • New Member
  • **
  • Posts: 4
  • Mole Snacks: +0/-0
Re: Chemical Forensics Questions
« Reply #8 on: July 31, 2011, 02:26:48 AM »
Sorry for the delayed reply, but I'm back to ask a couple more blood-related questions.

Which of the following would bubble if submerged in hydrogen peroxide: ketchup, paint, rust, barbeque sauce, and/or a fresh tomato (smashed). I know it has to do with which ones contain catalase, but Google's not being cooperative and isn't providing the answers easily.

Also, a couple posts back, rjb suggested that an LGM test could potentially be created by mixing malachite green, acetic acid distilled from vinegar, and zinc. Suppose my novel's character could come up with those three things -- would it be as easy as tossing all of them in a glass and stirring it up? The scene that I've conjured up so far is that my character is in a house and they find malachite green by the homeowner's fishtank; next, they distill some vinegar and mix it with the malachite in a glass, then drop a few pennies inside (US pennies are made of zinc apparently). Again, because of dramatic reasons, this character would not have time to run to the store to grab anything else and, since they don't have any presumptive tests handy, they must use things only found around the house. I can take some creative license (like finding malachite green by a fishtank), but I want it to be at least semi-believable. So I guess my main questions are: 1) How would they combine this solution? and 2) If these ingredients could work, what are some rough rough measurements? I.E. how pennies would be needed?

Thanks for continuing to field my odd questions!

csiguy55

  • Guest
Re: Chemical Forensics Questions
« Reply #9 on: May 16, 2012, 10:19:51 AM »
I find it very interesting what the real ways that people can test blood and other samples from crime scenes compared to what the average person would think. Based off tv shows and what they read online, we only know the small facts of what happens with either deceased bodies, blood samples or how crime scenes are handled. I think based off what rjb posted below me it'd be a very interesting and fun job to have in this industry http://www.atf.gov/careers/forensics/ after completing a degree in the forensics field. If you are interested in this field of study check out (spam link deleted) which answers any questions you may have in regards to the forensic industry, career opportunities and different programs that offer these kind of degrees.    
« Last Edit: May 16, 2012, 12:24:46 PM by Borek »

Offline Babcock_Hall

  • Chemist
  • Sr. Member
  • *
  • Posts: 4195
  • Mole Snacks: +263/-17
Re: Chemical Forensics Questions
« Reply #10 on: May 16, 2012, 11:12:16 AM »
I am not sure why this thread got bumped, but I just wanted to emphasize a point that has already been made, that the KM test and others like it are presumptive tests, not confirmatory tests.  The review article by Virkler and Lednev already cited is a good source of information on this topic.

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 25831
  • Mole Snacks: +1690/-401
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Chemical Forensics Questions
« Reply #11 on: May 16, 2012, 12:25:15 PM »
I am not sure why this thread got bumped

To post spammy link to the user site.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline Babcock_Hall

  • Chemist
  • Sr. Member
  • *
  • Posts: 4195
  • Mole Snacks: +263/-17
Re: Chemical Forensics Questions
« Reply #12 on: May 18, 2012, 06:55:29 PM »
rjb,

The subject of false positives and the KM test sometimes comes up.  Reduced phenolphthalein (phenolphthalin) will slowly oxidize in the air, even in the absence of blood.  Your protocol does not give a recommended maximum time, beyond which the observation of a pink color would not be trusted.  I was just curious how long you used.

Offline rjb

  • Regular Member
  • ***
  • Posts: 65
  • Mole Snacks: +8/-0
Re: Chemical Forensics Questions
« Reply #13 on: May 21, 2012, 08:39:38 AM »
rjb,

The subject of false positives and the KM test sometimes comes up.  Reduced phenolphthalein (phenolphthalin) will slowly oxidize in the air, even in the absence of blood.  Your protocol does not give a recommended maximum time, beyond which the observation of a pink color would not be trusted.  I was just curious how long you used.

BH,

Now that's a very good question... In most cases, pretty much regardless of dilution factor (up to ~1:10,000), a colour change occurs (with both LMG and KM) within 5-10s. I typically advocate the use of a 30s cut-off after which any colour change reaction is described as 'inconclusive' or 'KM/LMG -ve' depending upon how the colour develops.

I tend to find that vegetable peroxidases produce a comparatively slow developing colour change (quite unlike that of blood) which takes more than 30s to develop, whilst oxidation from air tends to begin to develop after a few minutes of exposure. I dispose of used filter papers before the oxidation process begins, so that I don't fool myself into thinking a reaction has taken place when in reality it's just oxidation... 

Kind Regards

R

Sponsored Links