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Life in the Drug Labs

Ah, Glassware

Well, while the mail continues to come in about my post yesterday, I’m going to pull back from the global perspective and zoom back into the glassware drawers of my lab bench today. A while back I wrote about the different sizes of ground glass joints that organic chemists typically use. People from outside the field are sometimes struck by the fact that we don’t have to do as much glassblowing and the like as they might have thought. Decades ago there was a lot more, but for a long time now we’ve been able to build up all sorts of apparatus (apparati?) by connecting standardized glass fittings together.
This has all sorts of advantages, letting us assemble odd custom configurations pretty easily, and change them without too much work. The downside is that the ground glass joints aren’t by themselves vacuum tight – not by the standards of inorganic chemists, for sure – and need to be anointed with thick, nasty vacuum grease before they can be trusted to that level. And if you don’t grease them for normal work, which we tend not to because the grease gets into your compounds, then the joints tend to freeze if left too long or too tight.
There are all sorts of voodoo tricks for unsticking them. I pride myself on being able to do it, but (objectively) I don’t think my success rate is all that greater than the norm. For the record, my technique is to put a few drops of silicon bath oil up around the edge of the stuck connection and let it soak in for a few hours. Then I rapidly heat the outside joint, grab it with a towel, and do the usual pulling and tapping while hoping for the best. There are better ways, but they’re typically found only in a glassblowing shop.
When I last wrote about this fascinating subject (hey, chemists like their glassware), I mentioned that I’d gotten in the habit of using 29/42 size joints. (That’s a measure of size: the first number is a diameter, and the second is the length or taper). That’s a larger one than is common in American labs; you see it more in Germany, among other places. I’m so used to it now that the standard 24/40 glass joints you see all over the place look narrow and shrunken to me – will I really be able to get my product out of that?
The standard small size these days is 14/20 – that’s the size of all our 5, 10, and 25 milliter flasks. (You can get 100 mL flasks (or larger) with that size joint, too, but they start to look disproportionate and weird, and there’s no real reason for large flasks to have such a small neck). In between that and good ol’ 24/40, though is the 19/22 size, which I really should look at again. It would be the wide-mouth counterpart to 14/20, in the same way that 29/42 is to 24/40. I’d probably like it.
But I’ve hardly seen a flask of that size since I was an undergraduate, and that whole range of glassware immediately recalls sophomore organic chemistry labs. I wondered why that was, but now I have the story thanks to reader Norm Neill of glassmaker NDS Technologies, who saw its birth at Kontes:
“The 19/22 Glassware kit was developed jointly by Eric Nyberg from Kontes Glass and Dr Howard Martin from Lake Forest College in the late 1950’s. . .they wanted to scale down the size of the glassware from the traditional 24/40 glassware to something smaller so it could be issued as a complete kit to a student and locked in his lab drawer. . .The next size down from 24/40 is 19/38 but the joint length was too long to allow us to scale down the kit (and) fit into a standard lab bench drawer. The 19/22 medium length joint was the best trade off at the time. . .The packaging of the kit was so popular that during the early 1960’s production had to be allocated. The overwhelming success of the 19/22 glassware started the development of an extensive line of 14/20 glassware under the Bantamware® brand.”
It’s my impression that the 14/20 glassware has been taking over the student market in recent years as well, what with the move to smaller and smaller amounts of solvents and reagents. That makes me wonder if 19/22 glass has a future, which means that I’ll probably find some lunatic reason to switch my small-scale stuff to it really soon, giving me the most oddball glass collection in the place. . .

26 comments on “Ah, Glassware”

  1. Merkwurdigliebe says:

    At a large pharmaceutical company in Nutley, NJ 24/40 glassware is smashed immediately upon discovery. 29/42 is preferred among the larger size. 14/20 is, of course, still necessary for smaller reaction. 19/38 joints were used on vacuum lines.
    I found that switching companies is made most difficult by having to grow accustom to the inferior 24/40 joints. Touting the advantages of 29/42 are met with blank stares, condescending looks, and that finger gesture that means “the monies.”

  2. yttrai says:

    Oh, the odd sizes have one major invaluable feature:
    No one will steal them, since no one else has compatible glassware!

  3. Nick K says:

    In Europe we have 24/29 and 29/32 joints, which are squatter, less prone to jamming, and look better, IMHO. I love 29/32 because the flasks go straight on the Buchi without an adaptor. Incidentally, whatever happened to Clearfit joints? As the name suggests, they were perfectly clear and smooth, being moulded rather than ground. A delight to work with, and they never jammed.

  4. philip says:

    There was a different and very practical reason that I heard 35 years ago for using 19/22 joints in the undergraduate labs. At the end of the year, when students had to cough up cash to pay for any glassware they had broken, they couldn’t steal it from the adjoining research labs, where they would only find the 14/20 and 24/40 sizes.

  5. HelicalZz says:

    If I had to pick one skill only that I most value from my undergraduate research project it would be glassblowing – even though I don’t do it anymore (at all).

  6. agogmagog says:

    To unstick a stubborn ground glass joint: Place dry ice on inside of joint. Allow to cool for 10min or so. Then apply flame to outside of joint (Bunsen burner or propane torch).

  7. CMC guy says:

    My undergrad institution switched organic lab kits from 19/22 to 14/20 the summer I worked in the stock room. I was able to salvage what ever I wanted of the old stuff so had quite a collection (and my odd look from my mother at what I brought home). Most items have gotten lost or damaged in various moves but I still have a complete intact kit that I hope to display rotating set ups one day once kids are gone and can have true home office.
    I know there was a push to go to micro glassware kits that never caught on as far as I can tell. It was fine is you knew what you where doing but the regular stuff was better for teaching novices.
    I had stopped using grease in favor of teflon tape/sleeves long ago except for when a strong vacuum required. My grad prof always chastised us (mildly) for NMRs with extra peaks from grease and/or solvents.
    Maybe another Lowe’s Law could be “A good glassblower is a chemists best friend”.

  8. MTK says:

    Instead of grease, I like those teflon sleeves that fit in the joint. I’ve never had a frozen joint using those things.
    In the 250 mL to 2L range we have 24/40 on most of our glassware and now it would be too expensive to change to 29/42. That’s too bad, because it also seems like most of our funnels and bigger spinbars are just a hair too big to fit.

  9. Mark M says:

    agree with MTK about the sleeves except in one of the few instances in which teflon reacts: Na, Li, or K in liquid NH3 (of course this is one of the only times you will also break out the glass coated stir bar)

  10. cookingwithsolvents says:

    29/26 (yes 26. . .much easier to deal with than 42) and 19/22 ALL the way. It is SO much easier to deal with solids and if you have oils and solutions you shouldn’t care, anyways.
    I use the heat gun on a frozen joint to get it very hot then heavy gloves to simultaneously pull and twist the joint free. Occasionally I’ll tap it here and there, too.

  11. milkshake says:

    You can easily shave off some teflon from large spinbar egg with a new razor blade – takes only about 5 min of work and you have one big stirbar that fits.
    After coming from Europe it took some adjustment to get used to 24/40, beilng longer and narrower than the stuff I was using before (the 29 joint).
    I still like to use 14/20 for reaction run on small scale, the distillatrions of few mL, small volume filtration etc.
    Joint compatibility is bit of issue especially for vacuum work (you combine pieces from two different manufacturers with supposedly the same joint and they dont always fit) so tend to buy everything jointed from Chemglass now, they have been pretty respectable.
    As for unstucking frozen joints, I use Dereks method, the direct flame heating is important, it does not work with a heat gun. I like to soak the frozen joint in kerosene or light mineral oil (like the petroleum that is used to package sodium lumps) bicause it has very low viscosity and soak in much better than silicone oil.
    (I wonder how the common household WD-40 in can would work instead of mineral oil for the purpose, I have not tried it yet.)

  12. Andrew says:

    Teflon sleeves are almost worthless when working on organometallics. Drying a pot of TBA-ReOCl4 on the Schlenk line, a ring of the yellow flakes nearest the Teflon sleeve turned black simply from the humid air leaking through.
    Try Krytox? No peaks near 0 ppm.

  13. Jose says:

    Tiny thread hijack- new book out, excerpted on the AP wires from of “snapshot of life in 2058 as envisioned by 60 top thinkers whose short essays make up “The Way We Will Be 50 Years From Today”
    Amusing, me thinks!
    1. We’ll all know our personal DNA sequencing, allowing medical treatments and health-prevention strategies to be tailored to our genetic profiles.
    2. Life spans will reach triple digits as we learn to reprogram cells to compensate for failing organs.
    4. The recognition that infection causes most chronic diseases will lead to vaccines against schizophrenia, bipolar disorder, heart disease, Parkinson’s disease, Alzheimer’s disease, obesity, multiple sclerosis, rheumatoid arthritis, dental caries, autism and some cancers. AIDS will be eliminated.
    10. Nanotechnology will let us turn information files into physical products. For example, we can e-mail a toaster and print it out on a desktop “nanofactory.”
    16. Nanotechnology will allow paralyzed people to walk. Molecules injected into the spinal cord will form into nanofibers that prevent scar tissue and promote new cell growth.

  14. Curious says:

    Why does Teflon react with Na, Li or K in NH3? I’ve always noticed that, but used the black stirbar anyways.

  15. MTK says:

    Yeah, I’ve done that to a number of spinbars. I just hate the way they look afterwards. I know it doesn’t hurt the reaction or anything, it just annoys me.
    Now that I think about it, I might take a few of those home with me and take my Dremel to them to smooth them out. I could bring my Dremel to work, but I’m not sure what I would tell the boss if he saw me spend a morning sanding spinbars. 🙂

  16. HelicalZz says:

    And by the way…. RB flask joints are the easy subject. Can someone explain to me (rhetorical) if there even exists any kind of standard for stopcocks on separatory funnels?

  17. Nick K says:

    Curious: alkali metals react with teflon by single electron reduction of the carbon-fluorine bond, giving alkali metal fluoride and (presumably) some form of elemental carbon. Back on topic now: beware of the larger egg-shaped spinbars as they exactly the right size to jam irreversibly in 29/29 sockets. I’ve ruined a number of flasks that way.

  18. MTK says:

    The stopcocks do have sizes as in a number 2 or 4. Stoppers have sizes that we’re all familiar with like a 22, 27, or 38. Of course, none of these numbers are the same as the joint sizes or correspond to any dimensions, even though they’re all generally the same shape, a truncated cone, properly called a frustum. I don’t know the origin of these, but a friend of mine always said, “If there’s an accepted, but F-ed up way of measuring something, it’s probably British in origin.”

  19. CMC guy says:

    HelicalZz I can offer operational sep funnel stoppers standards based on experience (may apply to stopcocks as well):
    Type 1: Leaks a little, wear nitrile gloves
    Type 2: Leaks a lot, wear nitrile gloves and apron (and curse)
    Type 3: Change clothes, and start reaction again (after going outside to curse) ALSO should throw away and not place back in general stock
    Type 4: Does not Leak, can’t remove without breaking stopper and/or funnel (back to curse)
    Type 5: Perfect fit/utility (rare of course, keep in cotton lined locked box to prevent breakage or theftage, you know what to do then)

  20. Anonymous says:

    stopcocks on sep funnels.. ARGH! now that is a sore subject indeed!
    Got into the habit of just leaving the damn thing assembled during washing if it wasnt too filthy just to avoid the headache of finding the perfect match again.
    came to love the glass stopcocks with very judicious use of grease on both sides of the hole. grew so damn tired of imperfectly fitting teflon ones with a funnel they didnt arrive with or whose orifice they no longer properly filled. (that doesnt sound right, does it)

  21. mrj says:

    I am surprised to find nobody mentioning Glindemann sealing rings ( They are just so superior to grease or teflon sleeves, there is no comparison. I don’t use anything else for high vacuum work (

  22. Anonymous says:

    On the topic of glassware….I was wondering if anyone knows of any good procedures for neutralising glassware.
    I’m having a bit of trouble with epimerisation in untreated or base-washed glassware while carrying out a reaction at 190 oC!!
    Any help would be greatly appreciated

  23. milkshake says:

    I would try to silanise your glassware – I think it is done by rinsing the glassware with a mix of Me2SiCl2 with tributylamine in dichloroethane, for about 10 min. There are commercial ready-made solutions of this kind – the silanisation is not very stable though and gets destroyed by base or acid.
    If you worry about basicity of KOH-washed glass I would try to give it a dip in 2M HCl after the alkaline soak bath and then maybe run the reaction under a CO2 baloon.
    The carbonyl epimerisation can be promoted by many things – high temperature, base, acid, polar solvents, lewis-acidic salts. I have not thought of glass but it is possible.

  24. philip says:

    Putting a silane surface on a lot of glassware is real easy if you have a vacuum oven and a good vacuum pump. Just toss all your (preferably clean) glassware into the oven. Put it under full vac and heat it up to 110 C for a day. Then, isolate the oven from the pump and inject about 15 mL of hexamethyldisilazane into the oven. Let it cook for a day at 110 C, then cool , vent and, voila, nicely silated glassware. It’s the only way to do hundreds of vials. I don’t know how robust it is but water beads up on it real different from normal glassware.

  25. LBB says:

    Can anyone help me with ground glass joints… If the US size of 24/40 is the same as Europe 29/32??

  26. LBB says:

    Can anyone help me with ground glass joints… If the US size of 24/40 is the same as Europe 29/32??

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