Xylene and "technical grade" N-Heptane were tested for purity. A glass slide was prepared by cleaning with dish detergent and dried with paper towel. Several drops of each solvent were applied to a glass slide and allowed to evaporate. Each left a faint shadow of an outline after evaporation. It's definitely something, but not much, and only visible when the light hits at a certain angle. The residue can be smudged with a finger. The slide feels dry, not oily and there is no residual smell. A taste was ventured and nothing was detected.

Could it be Ok?

MSDS for the Xylene

No MSDS yet for the Heptane but will ask. Here is a link to the Mfg's product page.

Further research shows that even the highest grades of heptane will leave some measurable residue, so can we really say If it leaves residues of any kind, dont use it?

This grade for liquid chromatography leaves 0.0002% (2 ppm) residue after evaporation.

This "reagent grade" leaves 0.001% (10 ppm) residue after evaporation.

The same manufacturer also has a life science grade that leaves only 0.0001% (1 ppm) residue after evaporation. Is that what should be used? It's only $122 for a half liter.

Question is, what's an acceptable level of residue left after evaporation? Is "not visually detectable" truly an appropriate criteria? Or would even 1 ppm residue levels still be visible?

Hoping this helps

One love

This is such a controversial topic with a lot of inconsistencies depending on who you talk to or read. I have tested a couple different sources now and the cleanest evap test I have seen is a ring or water mark. Every single clean evap test I have seen online (whenever actual pics are posted) have a ring. I have tested some that leave a visible residue and of course those are set aside for cleaning or degreasing stuff. I am currently using Klean Strip VM&P Naphtha, one that seems to be recommended quite often, and is the cleanest evap test I have personally done. I took a cosmetic mirror, thoroughly wiped down with 99% IPA (which also evaporated to leave a ring) and then dropped several drops in the center to form a puddle and let it sit while I went to work in the home office. Came back about an hour or so later to a large misshaped ring in the center of the mirror. I tried it with fewer drops and I still get the same type of ring, just smaller. There is absolutely no residue inside the ring. You cannot feel it when you scrape your nail or finger across it, but you can see it. Bestine did the same thing for me.

I am not saying all this to say that it's fine, but rather to expand this conversation. I know there are already threads for this type of conversation, but I feel like this particular question never really has a clear answer, at least not one that makes sense to me. Aside from spending a ton of money on medical supply grade stuff (which I have not tried so I cannot say whether it leaves a ring or not), I have no idea what the absolute best practice is because the answer is always, "if it doesnt leave a residue...". What I would love to see are pics of these top shelf product evap tests. Or pics from people who claim that their solvent leaves no residue.

Are there any nexians here that have evap tested a solvent that truly leaves absolutely nothing on the mirror or glass? If that is the case, then I will continue my search and then re x my entire supply when I find what I'm looking for, but for now, I have been using spice extracted from solvent that does leave a ring.

I think some barely visible smudges are fine. Some of it could even be water/dust from the environment (absorbed and concentrated by the colder evaporation spot).

I consider the test passing if nothing visible is scraped up on a razor blade. That's what we are going to smoke/ingest anyway.

Now THAT is the kind of specificity I have been looking for.

Thank you.

And that is essentially what I figured and I think what confuses a lot of people. It makes me wonder how many people have thrown out good solvents because they misunderstood what "no residue" means. I have been extremely over cautious about stuff since my cancer scare and surgery. Even recrystalized an entire supply losing about 2/3 of product because I needed to certain it was clean lol. I went crazy retesting my solvents too, almost threw out my current supply and solvents because of the ring and then spent a good two hours reading comments and looking at pics before I convinced myself it is probably fine for those same reasons you mentioned.

I second this. It seems that if the ring left was really the solvent (and not dust and moisture particles), then the ring should be filled in, ever so slightly, because the solvent would have sat in that space too. In other words, if it did not evap clean the there should be a residue patch instead of a ring.

One love

Detergent leaves a residue which becomes visible when displaced by solvents. Glassware for wastewater detergent analysis is routinely washed with hydrochloric acid before use.