We are doing a GC/MS demonstration lab for some students from an advanced placement high school chemistry class. We would like to do something that would interest and excite them about chemistry. Any ideas for things we could analyze that would impress them. We have done some other labs for this group and they are impressed by things that they see as useful and that they can relate to .

bill tindall bjtindall@mindspring.com

How about comparing fatty acids in butter with those in sunflower oil? Transesterify the lipids with BF3/MeOH . . . . Should be a splendid demo for essential FA contend of food, GC, and MS.

household items would be good:

-ether extraction of orange juice (or other drinks), look for limonene and other stuff. They would get to learn about sample prep issues here.

-perfume, complex sample, but probably a pretty neat chromatogram with a bunch of identifiable peaks

-gasoline, maybe not so good for id purposes, but easily available and more fun that looking at "mixed xylenes"

-mineral spirits for a hydrocarbon series, maybe compare to naptha to see the lower hydrocarbons in naptha and higher hydrocarbons in mineral spirits

-household cleaning products such as Formula 409. Should be able to see some glycol ethers here.

-THF or ether extraction of some plasticized PVC product and look for phthalates. These chromatograph well on a 5% diphenyl/95% dimethyl polysiloxane column. Tygon tubing or an old electrical cord (computer cord) sheath would be easy to find samples.

-fatty acids in foods (I saw HW also mentioned this). Do the separation of the acids and then derivatize to see how peak shape improves with the methyl ester (nonpolar column). I would use a quaternary ammonium method for simple derivatization. Make the tetramethylammonium salt with a little excess of tetramethylammonium hydroxide and the salts will quantitatively crack to the methyl ester in a hot injector (~250C+ or so). For fun, do the same thing with an a few different tetra-alkyls and see different spectra for methyl vs. ethyl vs. propyl. Could even add some phenolphthalein to the mix and make sure the mix is slightly basic and a small titration lesson could be had.

-call up J & W (or your favorite GC column supplier), they would definitely have some ideas about neat, demonstrative separations with interesting MS responses. I have a catalog at work with hundreds of test chromatograms. I'll flip through it and see if anything jumps out at me.

Spencer:
We have tried sundry quick esterification or transesterification methods and quickly dropped all of them, the last being trimethylsulfonium hydroxide. This last one prompted posting of questions in several groups. Nobody could provide unequivocal evidence for its robust use, some also acceeded to problems. Thus it would be very interesting to see any convincing evidence that the TMA-OH works, ROBUSTLY.

HW,

I actually don't know how robust TMA-OH would be in long term situations, but I have used it once or twice on rosin acids and it seemed to work OK. For "real" work, I would turn to dimethylformamide-dimethyl acetal, but I hesitate to suggest using such an alkylating agent at the high school level. Of course there's diazomethane for methyl ester formation, but my previous point holds true here about dangerousness in untrained hands... I strayed away from BF3/MeOH when I was doing this sort of work, because of the literature saying it had a propensity to do some rearranging of certain di-unsaturated fatty acids that I was concerned with at the time. Other than that, I would say BF3/MeOH would be fine choice as well. I made the TMA-OH suggestion due to its utter simplicity at getting decent results in Bill's application...

Spencer,
ok, then TMA-OH is also one of those quickies which are useful if you are not super serious and the if if if ifs are kept constant.
But now you got me curious about DMF-DMA. Pierce used to advertise this as reacting instantaneously with FA (not esters!), they have been more careful recently, stating that it "rapidly...converts..." It turns out that it does not react with FA at RT (you need a highly reactive carboxyl for reaction: Eschenmoser, et al, Helv Chim Acta, 48, 1746 (1965)). We noted that it reacts in the injector at 280+°, and then with esterified lipids as well (J Chrom, 228, 75 (1982)). How do you use it? For acids, esters? What temp.?

Incidentally, diazomethane is good (very good) only for acids it does not react with the inactive esters usually found in lipids (J Chrom B, 679, 208 (1996)).

I used DMF-DMA on rosin acids and fatty acids (tall oil acids) and I typically heated in a heating block at 80C for 30 min. I tried it without heating and did NOT get instant conversion - the recoveries varied; consistent with your comments. I have a reference at work and if you're interested, I'll attempt to find it in the bowels of my desk. The procedure outlined in that paper worked very well for quantitative analysis of real-world samples.

Thanks, Spencer.
If you find the mentioned paper it would certainly be interesting to see the refs therein.

Hans