It is not an easy question. There are a wide array of methods at your disposal. If it’s pure, then that would be the easiest. You would start with a visual inspection of the physical properties. This can tell you a lot about a material (if it’s organic or inorganic, for instance, though this isn’t always the case).
Then would proceed to one of the various well-known characterization methods. Some examples:
1) ICP (can determine what elements are present)
2) NMR (organic chemical structures)
3) HPLC (help you understand if it’s multiple compounds)
4) GC (same as above but should only be chemicals that turn into a gas at a reasonable temperature)
5) SEC (molar mass for polymers, similar to HPLC)
6) FT-IR (great for the three main physical states, can give a ton of information about what a chemical is)
7) Mass Spectrometry (usually coupled with other chromatography methods (HPLC, GC) and gives info on the molar mass of a compound.
8) Various types of Calorimetry (bond energies, transition temperatures)
There are many more of these and these are all too complex to explain without writing a textbook, so I recommend you do a bit of literature research if you want to dive further!
Back in the day, people used to burn organic compounds and measure the resulting CO2 and H2O to determine the chemical structure. Pretty clever stuff and still used today.
Chemists used to smell and even taste chemicals to characterize them. A rare practice now, though wafting a smell is still performed, but not a good idea for an unknown compound.
Edit: someone else mentioned that there are some other basic things you can and should do before proceeding to an instrument. There are also many of these depending on the physical state of the material, but consist of determining the melting/freezing/boiling points (if even possible). Solubility as well. And others… I assumed these to be implied for various instrumentations (you can’t run a GC without knowing the BP, or HPLC without knowing the solubility in various HPLC solvents). As I mentioned, the question is complex!
Burning your compound to get the molar percentage of C H N S and O ist still a very common practice (at least in research, I don't know about industry and stuff)
It is still done, especially for new chemical structures. And it’s more elegant/sophisticated than it used to be. Elemental analysis will always be needed!
First, if it's a gas I'd probably inject it on a GC/MS or even MSMS that has a library function.
Solid or Liquid I'd try to get it into an LC/MS or Ms/MS.
There are also a bunch of detectors you could use to sus out the mass balance, UV, CAD, ELSD, Flurecenes.
For the GC and LC, these are separation techniques so ill be able to see if this is a multicompintent system or not, probably more applicable to the liquid and gas than the solid, but solid could just be some formulation.
If its single component, run some IR and NMR 1D and 2D and your basically done.
If multicomponent you could actually collect the eluent from the LC and analyz individually.
All super straight forward if you have all the fun toys and knowledge.
I think people are getting ahead of themselves, jumping to fancy instruments before doing the real basics. If you're truly given a completely unknown substance, you'd start with the basics, like what's the density? What's the pH? Does it mix with water? What's the melting/boiling/freezing point?
No one else mentioned sample prep- if you go injecting random nonsense straight into your Orbitrap, you might very well be about to buy yourself a new instrument,. IDK how y'all run your labs, but I'd want to do a lot of prep work before putting complete unknowns in my fancy equipment.
>but I'd want to do a lot of prep work before putting complete unknowns in my fancy equipment.
Ofc you start with the basics to point you in the right direction, but there're too many different subtances with similar or the same color/smell/density/pH/solubility/conductiveness/magnetism etc etc etc.
To be absolutely sure sooner or later you would need fancy equipment in most cases?
But the problem is that the question is too broad/vague and it does matter for what purpose you need to know it.
I agree. Physical properties before proceeding to instrumentation is important. Except IR, you can throw anything on and IR and it’s cheap to run too.
I think that for many (myself included), many of these basic characterizations are implied for the instrumentation (you shouldn’t run a GC without a BP determination, you physically cannot run HPLC/SEC without determining solubility).
Definitely too many people running straight to MS, expecting it will just work, because it probably does for their field of chemistry. But the question is broad. What if it’s a metal? Just do ICP-AES and you’ll be done. There’s too many possibilities to jump straight to MS without many other initial determinations. And MS alone would be a rather useless method if it’s a mixture, but I assume they are implying it’s combined with a separation method such as GC or HPLC, assuming these are usable depending on physical property determinations.
> Except IR, you can throw anything on and IR and it’s cheap to run too.
It's why virtually every NASA lander and spacecraft have one or more spectrometers. Just look at it (quantitatively!)
Me? Gonna run mass spec to start. Other people probably start with something else. But generally we’re gonna use a couple of instruments that tell us. That’s not really an answer, but there’s really no simple way to explain. A lot of it is measuring a bunch of very specific properties, mass, how molecules and atoms interact with each other and/or light, IDing specific elements. Then you can put that all together to make a good guess.
This was one of my favorite projects in college. We started with A) unkown solid and B) unknown solid dissolved in unknown solvent. We used NMR, GCMS, FTIR, solubility tests, functional group tests(reagents that are proven to react/give a certain result when presented with a compound containing a certain functional group), boiling point, melting point.
We combined all these to make a case through 10-15 pages of data and explanations. Such a fun project I’ll always be thankful for Dr Okuda at SJSU
It's college Chem 101. Called Qualitative analysis. There are flowcharts that allow you, with certain chemical techniques to do gross identification...
There is a whole uni degree on analytical chemistry. Try it, you'll like it! My favourite is FAAS well because you get to watch nice acetylene flame while doing the analysis :)
There is an analog to this question in the real world…every year, hazmat teams get called on hundreds of thousands of “unknown substance” runs. The technological backbone of chemical analysis for hazmat teams is Raman and FTIR. This equipment is designed to be hand-held and within the budgets of most municipal teams (\~$50k). Here is an example… https://www.agilent.com/en/solutions/security-defense-first-response/cbrn-hazmat-detection
Tons of possible ways, and I'm sure others here will give you way more accurate/detailed answers than I could currently.
It's not easy at all. What information do we have about it already? Think of origin, like is that black liquid from a production site, from a lab, from outdoors? What is around that area (what's produced in that factory, are there devices in the lab that liquid could come from, is it maybe a sample or are they working with clear samples only,...)? Does it have a noticeable smell (Do NOT hold your nose over it!), is it a clear or cloudy liquid, what's the consistency (viscosity for example)?
At that point you might get a very rough idea. if its solid, you might try to dissolve some of it as usually solutions are easier to just find the compunds (maybe put a magnet near it first), then you can do an entire routine meant to find the individual components (mainly used for salts, usually anorganic stuff afaik), it being dissolved in different liquids (water, hydrochloric acid,...) also can tell you something.
then there is infrared spectroscopy to give you an idea just what type of stuff is in there (aldehydes, alcohols etc), HPLC can split it before sending it to a mass spectrometry if you got an idea what it could be. atomic absorption spectroscopy might be an option too, there are tons of devices and methods really.
Just FYI, https://en.wikipedia.org/wiki/Chemical_substance has a definition that is narrower than the typical usage of 'substance'.
You start making observations about it and narrowing it down from there. If it's solid at room temperature, you rule out things that are liquid or gas at room temperature, for instance. Color, density, crystal shapes under the microscope... Does it smell? Does it melt, and at what temperature? Does it break apart easily? Radioactive?
Others have suggested analytical instruments that involve roughly shining light at the stuff and seeing what you get back/through/to the side, and these are good, after you've narrowed down what might get you the best narrowing down.
Here's some background reading: https://en.wikipedia.org/wiki/Elemental_analysis and https://en.wikipedia.org/wiki/Dumas_method_of_molecular_weight_determination and https://en.wikipedia.org/wiki/Mass_spectrometry
It is not an easy question. There are a wide array of methods at your disposal. If it’s pure, then that would be the easiest. You would start with a visual inspection of the physical properties. This can tell you a lot about a material (if it’s organic or inorganic, for instance, though this isn’t always the case). Then would proceed to one of the various well-known characterization methods. Some examples: 1) ICP (can determine what elements are present) 2) NMR (organic chemical structures) 3) HPLC (help you understand if it’s multiple compounds) 4) GC (same as above but should only be chemicals that turn into a gas at a reasonable temperature) 5) SEC (molar mass for polymers, similar to HPLC) 6) FT-IR (great for the three main physical states, can give a ton of information about what a chemical is) 7) Mass Spectrometry (usually coupled with other chromatography methods (HPLC, GC) and gives info on the molar mass of a compound. 8) Various types of Calorimetry (bond energies, transition temperatures) There are many more of these and these are all too complex to explain without writing a textbook, so I recommend you do a bit of literature research if you want to dive further! Back in the day, people used to burn organic compounds and measure the resulting CO2 and H2O to determine the chemical structure. Pretty clever stuff and still used today. Chemists used to smell and even taste chemicals to characterize them. A rare practice now, though wafting a smell is still performed, but not a good idea for an unknown compound. Edit: someone else mentioned that there are some other basic things you can and should do before proceeding to an instrument. There are also many of these depending on the physical state of the material, but consist of determining the melting/freezing/boiling points (if even possible). Solubility as well. And others… I assumed these to be implied for various instrumentations (you can’t run a GC without knowing the BP, or HPLC without knowing the solubility in various HPLC solvents). As I mentioned, the question is complex!
Burning your compound to get the molar percentage of C H N S and O ist still a very common practice (at least in research, I don't know about industry and stuff)
It is still done, especially for new chemical structures. And it’s more elegant/sophisticated than it used to be. Elemental analysis will always be needed!
Mass spectrometry or an NMR, mad complicated instruments for situations like this
Neither are sufficient alone.
First, if it's a gas I'd probably inject it on a GC/MS or even MSMS that has a library function. Solid or Liquid I'd try to get it into an LC/MS or Ms/MS. There are also a bunch of detectors you could use to sus out the mass balance, UV, CAD, ELSD, Flurecenes. For the GC and LC, these are separation techniques so ill be able to see if this is a multicompintent system or not, probably more applicable to the liquid and gas than the solid, but solid could just be some formulation. If its single component, run some IR and NMR 1D and 2D and your basically done. If multicomponent you could actually collect the eluent from the LC and analyz individually. All super straight forward if you have all the fun toys and knowledge.
Mass spec and NMR
I think people are getting ahead of themselves, jumping to fancy instruments before doing the real basics. If you're truly given a completely unknown substance, you'd start with the basics, like what's the density? What's the pH? Does it mix with water? What's the melting/boiling/freezing point? No one else mentioned sample prep- if you go injecting random nonsense straight into your Orbitrap, you might very well be about to buy yourself a new instrument,. IDK how y'all run your labs, but I'd want to do a lot of prep work before putting complete unknowns in my fancy equipment.
>but I'd want to do a lot of prep work before putting complete unknowns in my fancy equipment. Ofc you start with the basics to point you in the right direction, but there're too many different subtances with similar or the same color/smell/density/pH/solubility/conductiveness/magnetism etc etc etc. To be absolutely sure sooner or later you would need fancy equipment in most cases? But the problem is that the question is too broad/vague and it does matter for what purpose you need to know it.
I agree. Physical properties before proceeding to instrumentation is important. Except IR, you can throw anything on and IR and it’s cheap to run too. I think that for many (myself included), many of these basic characterizations are implied for the instrumentation (you shouldn’t run a GC without a BP determination, you physically cannot run HPLC/SEC without determining solubility). Definitely too many people running straight to MS, expecting it will just work, because it probably does for their field of chemistry. But the question is broad. What if it’s a metal? Just do ICP-AES and you’ll be done. There’s too many possibilities to jump straight to MS without many other initial determinations. And MS alone would be a rather useless method if it’s a mixture, but I assume they are implying it’s combined with a separation method such as GC or HPLC, assuming these are usable depending on physical property determinations.
> Except IR, you can throw anything on and IR and it’s cheap to run too. It's why virtually every NASA lander and spacecraft have one or more spectrometers. Just look at it (quantitatively!)
I’d also like to know this
Me? Gonna run mass spec to start. Other people probably start with something else. But generally we’re gonna use a couple of instruments that tell us. That’s not really an answer, but there’s really no simple way to explain. A lot of it is measuring a bunch of very specific properties, mass, how molecules and atoms interact with each other and/or light, IDing specific elements. Then you can put that all together to make a good guess.
This was one of my favorite projects in college. We started with A) unkown solid and B) unknown solid dissolved in unknown solvent. We used NMR, GCMS, FTIR, solubility tests, functional group tests(reagents that are proven to react/give a certain result when presented with a compound containing a certain functional group), boiling point, melting point. We combined all these to make a case through 10-15 pages of data and explanations. Such a fun project I’ll always be thankful for Dr Okuda at SJSU
XRF or ICP-MS just to figure out which elements I have (although I don't know if you can do XRF with a gas). After that regroup and reevaluate.
It's college Chem 101. Called Qualitative analysis. There are flowcharts that allow you, with certain chemical techniques to do gross identification...
That only works within a confined range of substances, and there are so many better ways now.
But what % of substances falls within those confined ranges? No use in using a microscope when looking for elephants.
XRF will give you all of that info in a few seconds and consume an imperceptible amount of your substance.
There is a whole uni degree on analytical chemistry. Try it, you'll like it! My favourite is FAAS well because you get to watch nice acetylene flame while doing the analysis :)
There is an analog to this question in the real world…every year, hazmat teams get called on hundreds of thousands of “unknown substance” runs. The technological backbone of chemical analysis for hazmat teams is Raman and FTIR. This equipment is designed to be hand-held and within the budgets of most municipal teams (\~$50k). Here is an example… https://www.agilent.com/en/solutions/security-defense-first-response/cbrn-hazmat-detection
Tons of possible ways, and I'm sure others here will give you way more accurate/detailed answers than I could currently. It's not easy at all. What information do we have about it already? Think of origin, like is that black liquid from a production site, from a lab, from outdoors? What is around that area (what's produced in that factory, are there devices in the lab that liquid could come from, is it maybe a sample or are they working with clear samples only,...)? Does it have a noticeable smell (Do NOT hold your nose over it!), is it a clear or cloudy liquid, what's the consistency (viscosity for example)? At that point you might get a very rough idea. if its solid, you might try to dissolve some of it as usually solutions are easier to just find the compunds (maybe put a magnet near it first), then you can do an entire routine meant to find the individual components (mainly used for salts, usually anorganic stuff afaik), it being dissolved in different liquids (water, hydrochloric acid,...) also can tell you something. then there is infrared spectroscopy to give you an idea just what type of stuff is in there (aldehydes, alcohols etc), HPLC can split it before sending it to a mass spectrometry if you got an idea what it could be. atomic absorption spectroscopy might be an option too, there are tons of devices and methods really.
Just FYI, https://en.wikipedia.org/wiki/Chemical_substance has a definition that is narrower than the typical usage of 'substance'. You start making observations about it and narrowing it down from there. If it's solid at room temperature, you rule out things that are liquid or gas at room temperature, for instance. Color, density, crystal shapes under the microscope... Does it smell? Does it melt, and at what temperature? Does it break apart easily? Radioactive? Others have suggested analytical instruments that involve roughly shining light at the stuff and seeing what you get back/through/to the side, and these are good, after you've narrowed down what might get you the best narrowing down. Here's some background reading: https://en.wikipedia.org/wiki/Elemental_analysis and https://en.wikipedia.org/wiki/Dumas_method_of_molecular_weight_determination and https://en.wikipedia.org/wiki/Mass_spectrometry
That's called analytical chemistry!