Chromatography Forum

Hi guys,

I'm fairly new to chemical analysis; it was a topic I chose for my end of semester project, and it's well over my level so I'm stumped on a lot of points.

My presentation to the class will be based on the hypothetical analysis of an unknown compound (I will act as though I do not know the identity of the chemical, but will reach it through analytical methods). I have chosen 2,4,6-Trimethylaniline, as it is simple enough for me to understand it's properties and be able to explain what happens in each of the analytical steps, but also complex enough that I hope I can go through a good sum of analytical techniques.

Below is my framework of the presentation; if it isn't too much, can someone look it over and tell me my mistakes? Thank you!

1, Explain the concepts of ground/excited states, and to use a flame test on the compound. (Just for a random demonstration)
- Should this compound show a yellow color in the flame? I will not have access to this chemical, so my demo will use substitutes (i.e. table salt) that will hopefully show the same color as the compound

2, Solubility tests:
- Not soluble in water, but very soluble in acetone
- Does this automatically tell me the compound is organic? If not, what simple tests can I do to confirm that it is organic?

3, Assuming that I know the compound is organic (need a method to determine that first)
- Dissolve in 6M NaOH - Soluble = acid (then dissolve in NaHCO3 to find strong/weak)
- 2,4,6-Trimethylaniline will be insoluble
- Dissolve in 6M HCl - Insoluble -> then dissolve in H2SO4
- 2,4,6-Trimethylaniline will be soluble
- Reach conclusion that it is a base, but can I automatically assume that it is an amine? Simply from knowing its basic and organic?

4, At this point, should I use a liquid chromatography machine to separate the sample? An university professor tried to explain to me how this works but I'm still confused. How would I know which compound is the one I want? Should I analyze all compounds separated? How do you determine the identity of the separated compounds?

5, Use ICP-atomic emission spectroscopy
- Determine metal composition
- Assuming results from chromatography is a pure sample: therefore no trace metals

6, ICP-Mass Spec
- Determine molecular composition, find molecular formula? Is that possible with mass spec?

7, Fourier Transport Infrared Spectrometer
- Determine bond types/locations, find structure of molecule = find isomer of the original molecular formula

8, Analysis complete?

Thank you for reading all of this. I'm sure there are many mistakes in there, so I hope you guys can help me out. Thank you again!

Damn, I was distracted with the identification of stocks. Who knows what lies where and when will it all end. Well, instruct youth on the right path.
Hello, tribe young and unknown.

There are no guys. Here, mostly adult uncles and aunts who have themselves have children and even grandchildren. So come on you stranger forum - just say "Hi" , or better yet, "Hello", "Good day" , "Regards Member, I have some questins"
It is a trifle. But in the future prove useful. 90% of any job is dealing with people.
I understand you newfangled product of the "Bologna Process " http://en.wikipedia.org/wiki/Bologna_Process , ie "bolonka " (
http://ru.wikipedia.org/wiki/%D0%91%D0% ... 0%B5%D0%B7 - lapdogs were withdrawn in the same city) ,or similar process, in the U.S., I forgot what it is called, had already begun under Reagan.
As in the university /university (old) design of scool process: first simple common bricks , secondry stand basic foundament , only after this bilding bild/ where the remains of the old theoretical school - half of the questions would not exist. Unfortunately, this process is now gripping the world. You're not first, you will not last. In general, after graduating from high school you have to teach yourself, teach yourself and then teach yourself(c Lenin 1870-1924 http://en.wikipedia.org/wiki/Lenin - russian revolutioner,worshiped with us as J Washington you ).More precisely, "teach myself"

1)Combustion of organic matter and color of the flame with metal ions is two different chemistry process.
2,3)Well, you never know what is "insoluble in water, soluble in acetone" . Cocaine base is insoluble in water and soluble in acetone. A cocaine hydrochloride is soluble, and here and there.This is not an indication of the substance but method of its sample preparation.
With fluids it is most convenient to work.
Its base .To say that this amine - need to communicate C-N(R ,R2)
4)What is going separeted to share?
5,6) Its first step. But not AS ,ICP- its method. Step is element analysis.
6,7)Well, get a bunch of peaks, more precisely a stack of papers. And "then depending on your head ?". If there is no knowledge about what these peaks mean - you can wipe out this papers of ass.
8)"Stand beside the gun - not to shoot a gun" c Mendeleev.
You were at the gun, memorized as it is called some of the mechanisms - the barrel, recuperator, the bolt. But how the gun you not understand and projectiles to shoot and understand "how the gun works", you also do not give.
Set down. Zero.

If this problem describes the student grade 6 schools, but with "university approach" to teaching it would have many options.

1) Describe how the substance is identified at the time of von Liebig, Butlerov and Markovnicov, Louis Pasteur. Whithout NMR, ICP and Fourer IR spectroscopy.
For example how to burn a substance in a crucible, and caught the combustion products of alkali and acid. As synthesized substance. Which on this basis to draw conclusions.
But for this we must be familiar with the chemistry. And to demonstrate - to hold a counter-synthesis based on xylene, methanol and nitric acid. Nitration, nitrosation and recovery is well described in Organikume-Bekker.It is true there must also keep the hands not of asshole rose.
2)How is it done now.
There will need to bring the spectra, tables for spectral interpretation and observers to decipher the spectrum of an unknown substance (at least as a dramatization).The main train with tables in advance and find the correct spectra, but it would be embarrassing.
Google translate, I corrected

WOW, DSP007...you come to this board with strange translations/citations of Russian jokes and then advice somebody not to say " Hi, Guys!". May be you need to learn first how people address each other in English speaking boards. There is nothing wrong to say "guys" or "folks". I think you know science well, but lack communication skills. Despite numerous request from numerous people on this board to tone down your style you continue doing this. I am already skipping all your replies and I believe a lot of people will do the same pretty soon.

Tiange

you can go by this by different approaches
like DSP007 said so impolitely you can first start by viewing things has they were done 1-2 centuries ago
this reminds me of my high school chemistry test were we needed to find out if we were given a 1st, 2nd or 3rd type cohol. the solution was found doing clever and simple "wet chemistry"

if your compound has something like that then use it. maybe the amin group?

these days we have an aray of high tech instruments do find out what stuff is made of
for example for simple small molecules with the use of FTIR, NMR and MS you can find their chemical structure. always have one of each in your pocket when you leave home
to know which type of instrument and procedure to use is mainly based on why you need it for?

the process is that of investigation.
and it is based on the what for?
my advice is to add a certain story for your work.
why do you need that compound? why were you asked to find out what it is?

here is a hint:
is it the result of an industrial process to market the compound?
is it an unexpected impurity for a certain process?
maybe you want to prove that it was a known impurity that you cleaned from a process? and you need to show indeed that it is out of there

also always try to show things by 2s
1st to show the possibilty, 2nd for confirmation

You need to get some advice from your tutor about how broad you should make this. You cannot possibly hope to cover the whole of analytical chemistry in one presentation.

As ummgvar said, you could do a historical perspective, analysis through the centuries, or alternatively you could concentrate on what a modern analyst might do with one particular application.

If you choose the latter, and use a small organic molecule as your example, then I think some parts of your work are best trimmed out to make room for others:

1, flame tests: I don't know many organic chemists who routinely set fire to their product (except by accident). Flame tests are very good for spotting some elements, but not so good for general organic analysis. Incidentally, I feel strongly that demonstrations should be genuine, and never artificial. If you do go ahead with this, and use salt, be honest: say you're using it as a flame test for sodium.

2, solubility; of limited value in pinning down what something is. Similarly acid/base. I don't want to undermine your interest in these simple and fundamental tests, but I doubt their value nowadays. They may help a little, but nowadays you would expect to use NMR, MS and IR in looking at any organic molecule, and all three will give you better clues about acid and base groups (simple example: in LC-MS most carboxylic acids will give good negative ions, often fragmenting by loss of 44, CO2, while primary amines will very often fragment by loss of 17, ammonia). Solubility is more a practical concern of finding some solvent in which we can handle the sample! Solubility in acetone unfortunately doesn't prove it's organic.

4, Chromatography. Chromatography doesn't tell you what a chemical is. It separates things. The retention time may be a clue to what it is, but because no chromatogram can be long enough to separate every chemical in the universe, chromatography can only identify a chemical from amongst a limited subset of chemicals known to separate in the conditions you choose. If you have a genuine complete unknown, then chromatography is most useful when the unknown is part of a mixture. That way, you can separate it from the mix, so down-stream analytical techniques only have to examine one unknown chemical at a time. If you absolutely know that your chemical is an amino acid, of course you can identify it by comparison of its retention time with those of a complete set of amino acids. If you want help in finding out more information about chromatography, you've come to the right board.

5, 6 Use ICP-atomic emission spectroscopy., ICP-Mass Spec . Yes, elemental analysis is valuable even with simple organics. It's good to know how much C, H, N, O is involved. Maybe mention how to convert from percentage content to a minimal empirical formula? Even without ICP etc., you can sometimes get a molecular formula from mass spec. Consider discussing exact mass; given mass correct to 3 or 4 decimal places, there will be limited combinations of elements that add up to exactly that mass. This is the area of ToF, Orbitrap, and FT mass specs.

7, Fourier Transport Infrared Spectrometer. Yes, this is valuable. (By the way, it's Fourier Transform, and the FT bit isn't really important; even before FT, people routinely used scanning infra-red spectrometers to identify the functional groups of organic chemicals)

8, Analysis complete? No, there are two big things that leap out at me as needing mention. Firstly GC-MS. For small organic molecules, GC-MS (Electron ionisation) yields a useful fingerprint of fragments that can be searched against many commercial libraries (NIST etc.). Secondly NMR, which is the lynch-pin of organic analysis. It's almost impossible to fully identify any non-trivial organic molecule without some use of NMR.

Good luck!

thank you everyone for your professional and speedy responses! it's all much appreciated.

Imh: Thank you for that detailed breakdown of the entire process. I agree with the genuineness of a demonstration, and I'll proceed through with that route. As for NMR, it's at a level that's too complicated for grade 11; rather than pretending that I know what I'm talking about, I'll most likely leave the details of that one out.

unmgvar: my group has come up with a kind of crime scene chemical analysis backstory. Not the best one, but it should work. We decided that rather than explaining each process independently, that we would show how chemists would use these techniques together on a sample in real situations. Your show by 2 rule is indeed what we are going to use to prove that the compound is organic, Would this work? :

Step 1: Show that the compound is a weak base through the solubility tests
Step 2: since most, if not all weak organic bases are amines, we can prove that it's organic through a carbylamine reaction. If it's positive, it's organic/amine; if it's negative, then it's inorganic.

DSP007: I appreciate your help greatly. Sir.

Tiange

so far you got the amine group
how do you get the methyls
anf the fact that they sit on an aromatic ring?

FTIR NMR and MS these days can easily show all of this and get you to get the correct compound and its structure.

FTIR will show all on the spectra that there is an aromatic ring, that there is an amine connected to this ring, and also the methyl on the ring
the NMR will confirm all of this and also show that there are 2 methyls there, because you will get a strong signal of those sepcific spins.
the MS will also confirm the presence of 2 methyls and not just one,

you can also go with again chemistry, in order to guide you and fruther prove your claim
for example after you think that the compound is an aromatic ring with an amine group to it, you can check it out by doing a chemical reaction
because of the presence of the 2 methyls you have a steric interfrence (the methyls are blocking the possibility of reaction with the amine)
so if you use a reagent that also has a large volume (with a 2 methylpropane for example) to it then the reaction will occur only very slightly if at all compare to doing the same reaction on aniline.

have fun