# Talk:Forensic chemistry

Well, there is aproximetly zero information about what really are chemical forensics, there are not mentioned fibers, glass, paint, metal, polymer . . . (and so on), FTIR is only one of the methods, and it is used for polymer investigation. 
I think this article must be expanded
The author does not seem to have a good understanding of his tools.  Not only does he make generalizations (not all mass specs use EI), but he is flat out wrong about the FTIR:
"The molecular bonds of all compounds react differently and create unique patterns upon exposure to a beam of infrared light. The unique pattern created is known as the fingerprint for that drug."
there are so many problems with that description, I barely know where to begin.  first of all, not all compounds absorb IR, although most compounds of forensic interest will.  
secondly, "react" is a bad word to use in this description, because anyone who can accurately claim to be a chemist knows that IR light does not have enough energy to essentially any chemistry (there is surely a counter example to this, but they are few).  
Thirdly, and most importantly, the absorption of IR light by a sample does not "create unique patterns."  Basically what I am saying is that FTIR does not work on the principle of emission, it works on the principle of ABSORPTION.  the pattern that you look at is the pattern representing the wavelengths of light that have been absorbed, contrasted with those wavelengths that have NOT been absorbed.  you are not looking at the pattern of light that was "created" by the compound when it was irradiated with light (emission).  In fact, when you are discussing a macroscopic sample (milligrams:  you are looking at ensemble properties, not single molecule properties) the EMISSION of IR light is a CONTINUOUS function of wavelength, because the sample, sample holder, hell the entire instrument is a blackbody, and therefore the discrete and highly specific pattern that you are hoping for does not exist for emission, only absorption.
also the grammar is kind of poor, not that I claim any better; that is why I did not edit the article.Gordonliu420 (talk) 06:42, 18 June 2008 (UTC)

So expand and change where needed. I did not write the original but have added forensic details.Peterlewis (talk) 06:54, 18 June 2008 (UTC)

Please explain why law enforcement tag has been removed from the article. It is a topic which should be studied by every investigator, police or otherwise. Peterlewis 17:08, 15 May 2007 (UTC)

Restored.  We have a lot of editors who make mistakes. Viriditas (talk) 05:30, 27 February 2013 (UTC)

Hello, I edited the definition of forensic chemistry because it was wrong (in the sense of the English Language). As I pointed out in the article, Forensics is anything of/or pertaining to the courts. This was hammered into me ever since my first day in college as a Criminal Justice major. I cringed when I saw that they had the definition wrong. Don't mean to step on anyone's toes, but I just had to fix it. Sorry and thank you.  — Preceding unsigned comment added by 68.201.116.160 (talk) 20:15, 2 October 2011 (UTC) 

This review is transcluded from Talk:Forensic chemistry/GA1. The edit link for this section can be used to add comments to the review.
Reviewer: Delldot (talk · contribs) 16:17, 23 October 2015 (UTC)

I will take this one on.  My first question is about how referencing works: many paragraphs have a reference in the middle somewhere, am I to understand it covers the whole thing?  What about paragraphs with two references in the middle but none at the end?  I prefer each sentence to have its own ref so there's no confusion or problem if the sentences get rearranged.  delldot ∇. 16:17, 23 October 2015 (UTC)

Hello again. No, I took your advice on my last GA review. The references are after sentences that contain information that could possibly be challenged.  If there isn't a reference the sentence, I believe the information is basic knowledge or can be gleaned from the main article regarding the sentence subject.  I may have missed one, and I can add a ref anywhere you think needs one.  It is a little difficult for me to separate what needs references and what is common knowledge since I have gone to school for forensics.  Any suggestions you have that will make the article better are appreciated. --Stabila711 (talk) 18:54, 23 October 2015 (UTC)
My opinion is when in doubt, cite.  My understanding is you would not cite a sentence stating the hand has 5 fingers, but more complex than that, go ahead and cite.  But it's definitely been a while since I've read these policies so I can be corrected if I'm wrong.  I don't know about relying on the other wiki articles, because what if they're not well cited?  delldot ∇. 19:31, 23 October 2015 (UTC)
Most of the ones you marked were a result of my old habit of referencing at the end when the reference covers more than one sentence.  I have fixed those.  The only one that I actually changed was the paragraph on the testing for alkaloids invented by Jean Stats. I removed the claim that was causing the issues and reworded the paragraph. Let me know what you think.  Also, I am not sure if I like the skinnier table.  On larger monitors it results in a whole lot of empty white space from the end of the prose to the see also section.  I may have to get used to that format. --Stabila711 (talk) 21:03, 23 October 2015 (UTC)
Oh, ok, great.  Glad the tags weren't too much of a pain.  Yeah, change the table however you think is best, I just saw it in my own browser.  I'm about halfway through, and I just have a few little wording comments for the time being.  Here's a few things:

This sentence is obscure to someone not familiar with the topic.  For example, a stretch of alkyl groups will result in a peak between 2,950 and 2,850 cm-1.  We don't know what the numbers or notations mean.  Maybe something more vague like "a signature peak in wavelengths specific to alkyls (950 and 2,850 cm-1)."  I'm not sure if that wording actually makes sense.
I added a link to wavenumbers. I was aiming for the sentence to pair with the picture.  The ATR FTIR spectrum for hexane has a peak between 2,950 and 2,850 since hexane is basically just all alkyl groups. If you have a suggestion to make this better explained please let me know.
I went through and defined the acronyms in the body because I was getting lost having to refer back to the lead.  If you don't like them repeated in parentheses in both places, what do you think about taking the parentheticals out of the lead?  The acronyms aren't used there anyway.
Done. Removed parentheticals out of lead.
Awkward sentence.   The wavelength of light that the sample is subjected to depends on which element is being tested for. Better to avoid passive voice when possible.
I was always terrible at passive voice. How does this sound, Each element has a specific wavelength of light that is used to force the atoms to a higher energy state during the analysis
That's fine if you're not concerned about the slight loss of meaning. Alternately something like Forensic chemists can test for each element by using the corresponding wavelength of light that forces that element's atoms to a higher energy state during the analysis?
You are obviously much better at this than I am. I tweaked a word or two but I really like your phrasing and have put it in.
presumptive tests have indicated the presence of a specific element of probative value to the case. Is there a simpler way to put this?
I have to think about that one. I was shooting for the idea that AAS is destructive so you don't use it as a fishing expedition.  You should have some idea of what you are looking for before you go ahead and destroy the sample with atomic absorption.  There are presumptive color tests that can be used to show the possibility of specific elements.  For example, if arsenic poisoning is suspected, you can run a color test to see.  If that is positive then, and only then, would you run AAS.
I just mean how would you explain this to someone  didn't understand "presumptive tests" and "probative value"?  Maybe something like to confirm the presence of a specific element that might be important in solving the case, after preliminary (or earlier?) tests have suggested it is probably present. Only not that terrible.
This is what I went with, AAS should be used as a confirmatory technique after earlier, preliminary, tests have indicated the presence of a specific element in the sample.  Preliminary or presumptive, same thing.  Since the paragraph then goes right into heavy metal poisoning with a list of elements I decided that saying "elements important/probative to the case" was redundant.
More to follow tomorrow.  delldot ∇. 22:01, 23 October 2015 (UTC)

Responses added. --Stabila711 (talk) 22:52, 23 October 2015 (UTC)
Added --Stabila711 (talk) 09:46, 24 October 2015 (UTC)


### Second part
Ok, here's a few more comments mostly around wording.  I'm kind of ill-equipped to peer review this I'm finding, but on the other hand I can definitely tell you what doesn't make sense to the uninitiated (I had ochem like 10 years ago).  So these are all really minor:

This can be used to investigate notes or fibers left at the scene.. what kinds of fibers? fibers of paper with ink on them?  Cloth?
Well paper is made of cellulose fibers but I was more leaning towards fibers in general with that sentence. Fibers is a generic word used in forensics to describe cloth, string, paper, ect. The sentence is not supposed to be specific since a crime scene can contain any number of things.
explain unfamiliar words inline; just a link to another article will require the reader to leave your article. e.g.:
by looking at the retention factor (Rf) for each extracted component
whatever solution is used as the mobile phase.
This is useful in drug analysis where the pharmaceutical is a combination drug since the components would elute at different times 
The most common type of detector is an ultraviolet-visible spectrometer 
I will work through the article and add explanations.
 Done
Awkward: The detector used by a specific lab is decided by the lab's funding and the exact work they are performing.  How about The choice of which detector a lab uses depends on its funding and the precision needed for the type of work it performs.
Fixed. Your wording is much better. Thank you.
other limiting factors, such as the age of the individual parts --parts of what? The machine or the sample?
The instrument. Parts have to be replaced every so often. Chromatography columns get dirty, spectroscopy light sources burn out, ect. I added "of the instrument" to the sentence in question so now the part reads such as the age of the individual parts of the instrument.
 GC-MS is also capable of quantifying substances which can be used by forensic chemists to determine the effect the substance would have on an individual. Let me see if I understand this: GC-MS is also capable of quantifying the substances in a body, to help forensic chemists determine what effect each substance would have had?
Correct, for example a DWI case where the suspect was suspected of driving drunk. The blood test and the analysis is what confirms or denies that. If the presence of alcohol is confirmed but the levels were too low to make a difference then DWI would not be the proper charge. Since these instruments can detect at such low levels it is necessary to quantify what they find. Or, if a suspected overdose body comes in and the tests confirm the person took cocaine.  If the levels of cocaine were far too low to have caused death, overdose (cocaine) would not be used as the cause.
Both of these examples are very helpful.  Any chance of adding one or adding wording to the sentence to clarify? delldot ∇. 01:04, 26 October 2015 (UTC)
See below on my plan to add a section on this.
The limit of quantification for GC-MS instruments is higher than the limit of detection I don't like 'higher': a higher limit sounds like it's better. Maybe 'coarser'? 'more gross'? 'less specific'? Or could you just say The limit of quantification for GC-MS instruments, unlike detection, is typically in the nanogram (10−9) range.
Hmm, I am not a big fan of this wording since it can detect in the nanogram range (and even lower) and the phrase "unlike detection" makes it seem like it can't. The idea I was aiming for was that GC-MS can detect substances down to a very low level. However, quantification (which is a large part of forensic chemistry) needs more.  It needs a 1,000 times more of the substance to quantify it accurately.  It is a much higher bar for quantification than detection.
Oh, good point. How about GC-MS instruments need around 1,000 times more of the substance to quantify the amount than they need simply to detect it; quantification is typically in the nanogram (10−9) range.  If this is too overwrought, we can just not worry about "higher limit". Or, what about The precision of quantification...is lower (worse) than that for detection? delldot ∇. 01:04, 26 October 2015 (UTC)
I went with the first one, and added "the limit of quantification" to the second part of the sentence. Can't really say that the precision of quantification is worse since it really isn't as long as it is above the limit of quantification.
There's a subfields section, but it's only got one field.  Are there more fields?  Or might it make sense to eliminate that header and just have the Forensic toxicology as a level 2 header?
I made it a level 2 header. That was a remnant from when I first started rewriting the page.
In general I'm finding as I'm reading that I want to hear more about the specifics of the crime investigation but I'm getting bogged down in the workings of each instrument.  e.g. there's one sentence, GC-MS can be used in investigations of arson, poisoning, and explosions in order to determine exactly what was used.  I'm like, what sorts of things might it detect? What would they do with that knowledge? I guess I'd like to see more about how a forensic chemist's work fits in with an investigation team's.  Does that seem doable to add a few sentences about that?  Maybe in the modernization section?  delldot ∇. 23:04, 24 October 2015 (UTC)

That is the problem with this topic. Forensic chemistry is such an instrument heavy subject that the entire process is about the instruments.  I can certainly add more detail about what can be detected.  Arson investigations would detect fire accelerants like gasoline, kerosene, ect.  Explosive investigations would detect explosive residues like RDX, TNT, C4, ect.  Poisoning investigations would detect exactly what poison was used.  I will add these tomorrow as I am going through and explaining terms.
Basically, forensic chemists are there to tell investigators what to look for or to confirm/deny suspicions.  If RDX was used in an explosive, that would narrow down the list of possible suspects considerably since RDX is a military explosive.  Unlike, TNT which is used by demolition companies. The detection of TNT would still narrow down the list of possible people but not as far as RDX or C-4.  During poisoning investigations, the detection of ricin would tell investigators to look for the precursors to ricin when they go through their suspect list (precursors being castor oil plants).  The same thing for arsenic and other poisons.  If arsenic is found and one of the people on the suspect list recently made a credit card purchase for a large amount of rat poison that is probably the person the police should be looking at.  Or if strychnine is used and one of the suspects just happens to have a strychnine tree growing in their yard (which outside of India and southeast Asia would not happen naturally). It is all about giving investigators a direction to work off of. Or if something is suspected (overdose, DWI, ect.) to confirm or refute those suspicions. --Stabila711 (talk) 07:42, 25 October 2015 (UTC)
Wow, I definitely think all that is extremely interesting and I would definitely like to see it in the article!  It would be great to have examples from history (e.g. a famous bombing) but either way it would be great.  Are you thinking of expanding the history section? Or adding an "as part of the investigative team" section or something?  Well I guess I'll wait and see.  delldot ∇. 00:05, 26 October 2015 (UTC)
I am going to add another section on this.  That should work out a lot of the questions on how they are part of the investigative team.  I have already decided to add a picture of the Oklahoma City bombing since the detection of ANFO at the site helped track down the people responsible and I already have a New York Times article as a source.  I am having a hard time thinking of a good header though.  Thoughts?
Nice! I guess the header will be determined by how you present the info.  Maybe something like 'Role in investigation'?  Or 'Notable examples'?  delldot ∇. 23:26, 26 October 2015 (UTC)


### third part
In the identification of unknown samples, protocols have been grouped into three categories based on their identification ability. I don't like 'identification ability', would it be accurate to say based on the precision with which they identify substances? or accuracy?
Accuracy would be wrong.  Category C tests are not accurate since they have a lot of false positives but they are precise since they will always have these errors.  For example, the color test for marijuana (the Duquenois–Levine reagent) will come up positive if there are some brands of coffee or aspirin in the sample.  Even if there is no marijuana present.  It will always have a false positive with these so it is precise but it is not accurate.  Perhaps it would be better to say "based on the possibility for a false positive"?
Sure.  Or "the potential for errors"? delldot ∇. 23:17, 26 October 2015 (UTC)
 Done
The references that just go to a webpage, like Mentalfloss or csi.net, are not the greatest, but I'm not too worried about replacing them since it's just that couple and it's not too outrageous of a claim they support. But if you do happen to come across a book chapter or review article that supports the same info it would be good to replace them.
I made sure to limit those to just basic definitions and, like you said, not too outrageous claims.  I can certainly look for other references.
That's all I got, but I'm eager to see the new info you mentioned above. It occurs to me you might even be able to add an image if you wanted, e.g. of the site of a bombing or fire. delldot ∇. 00:53, 26 October 2015 (UTC)

Added responses to both sections. --Stabila711 (talk) 03:15, 26 October 2015 (UTC)
Sorry it took so long, real life got in the way. Let me know what you think of the new section. I am thinking of what else I can add to it.  Any suggestions would be appreciated. --Stabila711 (talk) 08:42, 28 October 2015 (UTC)

No problem, I was busy too.  I love the new section.  A couple thoughts:
Do you think it would be good to mention ANFO in the body as well as the caption, and how/why it led to the suspects?
So I had to change the caption to remove the claim that the ANFO helped lead them to the suspects. After rereading the New York Times source it was clear that the detection of ANFO didn't really help catch them (the source can still be used though as it confirms ANFO was found). They were caught for doing stupid things afterwards.  Debating on removing the photo altogether.
Be nice to have a cite for the drug/alcohol para.
Done. Finally found a world chart for BAC limits. Took me a while but I found one from the World Health Organization.
Explain what 'identification cases' are, since this is unclear: In identification cases, the determination of the substance that was used can tell investigators what to look for.
Sentence rewritten as In cases where an unknown substance is found at the scene, the identification of the substance can tell investigators what to look for during their search
delldot ∇. 16:54, 29 October 2015 (UTC)

Responses added. --Stabila711 (talk) 11:34, 30 October 2015 (UTC)
Fantastic.  Thanks for all the hard work on this, I know it was a slog.  I have nothing left to quibble about.  I have made some edits, as always feel free to make any changes to my edits if they need it.  Promoting now.  delldot ∇. 16:19, 30 October 2015 (UTC)
Great! Thank you for all the work on your end too. I appreciate all the assistance. --Stabila711 (talk) 16:30, 30 October 2015 (UTC)

A proposal has been made to form a WikiProject for forensic science. Please add your name to the list if you wish to contribute to this endeavour. TimothyPilgrim (talk) 17:26, 22 September 2020 (UTC)