So if I could sweet-talk GC-MS and LC-MS-MS techs at work into testing my e-liquids, unofficially, does anyone have suggestions for which columns and conditions to use? Also, which would be the most interesting compounds to zoom in on (I don't care about PG, VG or nicotine since I already know they are there)?
What would you look for and how?
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I guess contaminants:
DEG - diethylene glycol
diacetyl - butanedione
pesticides - chlordane,
www.who.int/heli/risks/toxics/bibliographyikishi.pdf
DEG - diethylene glycol
diacetyl - butanedione
pesticides - chlordane,
www.who.int/heli/risks/toxics/bibliographyikishi.pdf
Both of these instruments need to be high-res enough to have a databank of compounds that the peaks can be matched with. I do not know the column oven protocols, but the compounds being analyzed for are not ultra-high masses or BPs, so I would start with a standard oven ramping protocol and carrier flow, and see what you get. The time consuming part of these is to find what works best, and that can sometimes be trial and error, depending on the machine. Low-res MS will not identify well, but should give accurate nic levels, if you find the 162 peak.
I'd start with a 5% diphenyl dimethyl polysiloxane phase. A real workhorse. Maybe 0.32mm I.D. x 30M length and run the helium around 1.5 cc/min constant flow. Just a steady ramp from the appropriate solvent focusing temperature up to around 330°C over an hour.
Kurt, I think I have to disagree about the ability of low -vs- high res to make good identifications. Running in full-scan mode, a low-res can identify quite well assuming a non-coeluted peak. With coelutions, even a high res instrument won't be able to sort out the mix of masses from the coeluting compounds and the library fits will be poor. So the real limiting factor would be the complexity of the mixture... thus the ability of the column to resolve the close eluters.
You want your library spectra to be run at a resolution similar to the resolution that you're using.
Generally, you'll find the higher resolution instruments running in a selected ion monitoring mode where only a small subset of masses are being scanned thus increasing the mass dwell time and sensitivity, and using the filtering capability of higher resolution to distinguish masses of interest from very close masses coming from coeluting non-interest compounds.
The mass filtering capability of a high res instrument comes into play when doing such a SIM analysis since at 1000 resolution (low res), mass 162.26 can be distinguished from a mass about 0.16 amu different (162.26/1000), thus if you're trying to look at mass 162.26, you'll be seeing a mass range of 162.10 - 162.42, thus non-interest coeluters can interfere if the mass is close enough to mass 162.26. Raise the resolution to 10,000 (high res), and discrimination increases to 0.016 amu (162.26/10000), thus lowering the indistinguishable mass range to 162.244 - 162.276. Much higher resolutions can be used, but with higher resolution, there is a sacrifice in sensitivity due to the physical focusing of the ion beam.
Kurt, I think I have to disagree about the ability of low -vs- high res to make good identifications. Running in full-scan mode, a low-res can identify quite well assuming a non-coeluted peak. With coelutions, even a high res instrument won't be able to sort out the mix of masses from the coeluting compounds and the library fits will be poor. So the real limiting factor would be the complexity of the mixture... thus the ability of the column to resolve the close eluters.
You want your library spectra to be run at a resolution similar to the resolution that you're using.
Generally, you'll find the higher resolution instruments running in a selected ion monitoring mode where only a small subset of masses are being scanned thus increasing the mass dwell time and sensitivity, and using the filtering capability of higher resolution to distinguish masses of interest from very close masses coming from coeluting non-interest compounds.
The mass filtering capability of a high res instrument comes into play when doing such a SIM analysis since at 1000 resolution (low res), mass 162.26 can be distinguished from a mass about 0.16 amu different (162.26/1000), thus if you're trying to look at mass 162.26, you'll be seeing a mass range of 162.10 - 162.42, thus non-interest coeluters can interfere if the mass is close enough to mass 162.26. Raise the resolution to 10,000 (high res), and discrimination increases to 0.016 amu (162.26/10000), thus lowering the indistinguishable mass range to 162.244 - 162.276. Much higher resolutions can be used, but with higher resolution, there is a sacrifice in sensitivity due to the physical focusing of the ion beam.
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Thank you, DVap. Excellent information! You are clearly more up on GC-MS details than I am. Its been about 7 years since I ran spectra for my organic classes on our Agilent GC-MS, and because it was for particular reaction mixtures and solvents, it was about as plug and play as you could get. During the later part of my grad work and then postdoc, I was asking one of the local organic chemists if they had GC-MS, and could they ID compounds. The response was no, because it was low-res, and it was LC-MS not GC-MS, so I took that to mean you needed high-res. Clearly I wasn't getting the whole story. Glad you are bringing more hands-on knowledge here.
Have a look also for Tin (and if there;s something there but perhaps not tin, what is it?).
It's a great chance to get such data. Do kee and post the original plots. Ans thanks for doing this.
+++
Oh, i see you will test the liquids not the vapor. In that case there won't be any tin. What might turn up post-vaping would be more of interest, but of course not so easy to arrange.
It's a great chance to get such data. Do kee and post the original plots. Ans thanks for doing this.
+++
Oh, i see you will test the liquids not the vapor. In that case there won't be any tin. What might turn up post-vaping would be more of interest, but of course not so easy to arrange.
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Reading kinabaloo's comment made me think that there may be an opportunity to test a given atomizers affect upon vapor produced by looking at a post-atomization condensate for the presence of additional elements and compounds.
Since Chem is not my field, take this mention with a grain of salt.
That said, I am happy to see the range of expertise participating in the vaping community.
Since Chem is not my field, take this mention with a grain of salt.
That said, I am happy to see the range of expertise participating in the vaping community.
There is a possibility of a trace of tin from soldered joints. From my own tests I know that the joins do heat up and the solder melts away from the hot nichrome. I wouldn't have expected any tin to get into the vapor stream but a GC trace did have a spike that if it wasn't tin had no obvious cause (but it could of course be some other compound).
Unbonded metals (transistion ones especially) in the vapor woud be bad news. But it's just a possibility.
just a post to keep this subforum on my radar! and a little disappointed in the sparse responses. i really had hoped that our american vendors would use this venue to show us what they are doing as to qc and testing.
alas, only nick from dc has shown an interest .......
alas, only nick from dc has shown an interest .......
Any updates with this?
Too bad I've been away from GC/MS and LC/MS for about four years now
. It is getting about time for another internal transfer; maybe get back into analytical
Too bad I've been away from GC/MS and LC/MS for about four years now
. It is getting about time for another internal transfer; maybe get back into analytical
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