I have a bunch of test tubes that have a zinc residue that I can’t get off with my usual bleach soak followed by alkaline and acid washes. It is from a nitrate test if that makes any dfference.
Are there any common solvents I should try before I break out the nasty sulfuric/chromic acid cleaning solution?
Hydrochloric acid might work, maybe even vinager.
Agree with Christopher, soak in 1M aq HCl overnight.
In my first week of my US postdoc I was amazed to see lab colleagues throwing used test tubes into the glass waste and just buying new ones. It truly is the land of plenty says I to myself.
Thanks, I’ll give it a shot.
It’s been a while since my organometallic cleaning days, but if the HCl doesn’t work, what about a KOH/EtOH bath?
Sulfuric acid/H2O2 is less nasty than the H2SO4/chromic combo (chromic acid being banned for general use at my facility), but only slightly.
I’ve got them soaking in 1M HCL now, but I’ll try KOH/ETOH if that doesn’t work.
How do you make the H2SO4/H2O2 mix?
But the combination of H2SO4/H2O2 is pretty serious nasty stuff. It is usually used to oxidize organics down to constituent parts (CO2, N2, etc). I don’t think it will work any better on dissolving Zn then just H2SO4 (or other acid).
In order to really get your glassware clean of nasty oily, greasy crap, or just basically destroy a sample to its basic components H2SO4/H2O2 is very effective. Its a common USP method. Its sometimes called “piranha” because it eats everything. And to do it right, you have to heat up concentrated sulfuric to a very dangerous temperature, and add concentrated H2O2.
Man, unless you know what you’re doing; I’d stay away from it.
Besides, you don’t need it…you want to get rid of a metal residue, not completely oxidize an organic sample. A simple soak in dilute H2SO4 is probably all you need (HCl should work too)
How much do test tubes cost? 5 cents? How much is the cost of the material and effort to clean them?
Which is why I *really * wouldn’t mess with the chromic acid, which I’ve been advised is worse than piranha from a safety standpoint. I’ve never had a problem mixing up a little to clean a frit, and I’ve never heated the acid.
My typical cleaning protocol (in order of cleaning difficulty):
Acetone
Water, then acetone
Soap and water, then acetone
50% NaOH, water, acetone
37% HCl, water, acetone
(occasionally I’ll try hexanes here if I know the residue is greasy)
Toss in a base bath overnight (I no longer keep a base bath, though)
Throw it away and order a new one.
But then, 1L 4-necked flasks cost more than test tubes. . .
Yeah, I don’t see the need for piranha mix and I’d stay away from it. Aqua regia would probably be a better choice if you want something more reactive.
They’re penny wise and pound foolish around here. Getting the $87 to buy 1000 tubes is next to impossible, and I don’t need that many. They would rather pay me more than the tubes are worth to try to clean them than replace them.
I wouldn’t break out the serious stuff just for the test tubes. I keep a stash of can’t-get-it-clean-otherwise glassware, and do it all at once. I keep reusing the same acid until it won’t clean anymore.
I’d second aqua regia. We used it dissolve thallium from plating material at my last job. Sadly my current lab has neither HCl or nitric acid, so I have to go the sulfuric route if I really want to keep something.