I did something a few days ago that I thought some of you might find interesting, and I'll post the results if anyone is interested in it.
Basically, I had the GC-MS at work down for maintenance, and since I otherwise had a lull in samples to run for it, I put a column in suitable for hydrocarbon analysis. I could probably find something better(actually I think I had something a little better) but I had an old Hewlett Packard HP-1 column already set-up and ready to fit. For reference, this is a .20mm ID column, 12m long, .14µm film. I have a similar 20m column that would probably be better, but it was untested and given my time constraints I didn't want to risk running it down.
I took two samples of gasoline, both collected on separate dates from separate stations. One was 93 octane from the Casey's up the road from me, the other 87 octane from Sam's Club. In both cases, I dispensed several gallons into my car before filling the containers to ensure I was not getting any left-overs from the hose.
Ideally I would have collected samples on the same day at the same station, but this is what I had to work with.
I can give full separation parameters if anyone is interested, but basically I injected neat gasoline at a 50:1 split ratio. This probably "loses" some trace compounds, but I didn't really have a suitable low-boiling solvent like CS2 on hand, and this let me look at basically everything there. I was able to distinctly see the ethanol peak, which has actually been quite difficult in the past when I've tried to analyze gasoline.
Among other things, across several runs for both samples, I looked at the extracted ion chromatogram(EIC) for m/z 45, a prominent ethanol fragment(and with little background spectral interference). Without further work, it would be difficult for me to quantitate the amount of ethanol, but the peak area was consistent(RSD~5%) across both samples over several runs. This tells me that both samples had similar amounts of ethanol, probably close to the stated maximum of 10%.
I analyzed both gasoline samples by feeding them into AMDIS, a software package that is able to separate mass spectra of co-eluting compounds and provide identification. I set the threshold for identification at an 80% quality match.
I found hydrocarbons as small as propane, along with a surprising amount of butane and isobutane in both samples. I had been under the impression that summer blends contained little butate. On the whole, though, I found similar hydrocarbon blends between both and overall they were more alike than different.
I'd like to repeat this with better chromatographic resolution, and I suspect that the real differences between the two are in compounds at relatively low concentrations, ones that disappear into the background and/or are at the limit of detection for a full scan method, especially on this relatively old mass spectrometer.
I realize this isn't anything groundbreaking, but thought folks might be interested in what I'd found just in playing for my own curiosity.
