Sometimes discussions get focused on the wrong questions, and for the purpose of this discussion may I suggest we discuss and answer the following questions:
1.0 Is there a significant difference in the salubrious/wholesomeness between n-propane, n-butane, and Isobutane?
1.1 Not according to governmental industrial hygienists.
2.0 Is there any advantage afforded by one, but not the others?
2.1 They all have different properties, starting with their effectiveness on the C-30 triterpene sized molecules like plant waxes and anthrocyanin plant color pigments, and ending with how easy they are to purge, while holding on to the monoterpenes.
As you lower the temperature, n-Butane gets too thick to pump, so we use up to 50% n-Propane to thin it down, and minimize pickup of molecules longer than C-21.
3.0 Is there a difference in the levels of unwanted longer chain hydrocarbon residuals in cheap versus certified reagent grades.
3.1 They are present in all grades at some level, but the 99.5% Praxair Instrument grade we get from Apis Labs tests at 99.9% purity as received, and it tests 99.995% relative to molecules longer than C-4, after we distill and post filter it.
Our results from lighter brand LPG mixed gases pretty much parallel the work done by Skyhighler above, which is to say that they don't typically have enough to exceed established Permissible Exposure Levels, but what is there is concentrated in your oil, and once you see, smell and taste it, you won't want it in your concentrate.
4.0 How consistent is their quality level?
4.1 Very consistent with the reagent grades that come with certifications and test results, but the bad news is that quality can vary significantly in lighter butane from Asia, per the above charts, as well as in refrigerant grades like R-290/600/600A, as evidenced by the episode with Ecogreens R-290 and 70/30 blend last year.
I highly recommend pre-distilling 100% of LPG used for extraction, regardless of source.
