What Do I Even Do All Day: Part 2
Sep. 25th, 2019 09:39 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
kaberettLast time I talked (in the main post) about weighing and digestion (and in comments about HF handling protocols), and left matters at "so now it gets to sit and stew in its own juices for 48 hours".
Which means that I return to twelve very small pressure cookers of rock soup, not to be confused with stone soup.
The first step is to lay out a bunch more Kimwipes inside the hood. The second is to, double-gloved, gingerly remove the vials from the hotplate and put them onto the Kimwipes. Again, you want to check your hands every ten seconds or so: although you can close the screw-cap vials pretty tightly, there's always a chance that you'll wind up with some of your hot acid mixture condensing around the cap and gradually working its way down the threads, all the better to drip on you. Which you don't want.
And you especially don't want that happening while it's still hanging out at 140°C, so having gently placed it down upon a piece of expensive glorified tissue, you leave it 20 minutes to cool down while you get on with other bits and bobs. (It is in the nature of the beast that there is almost always something else to be doing, and usually it's beaker cleaning, but now is also the point at which you increase the hotplate temperature to 150°C for the next step, and ideally sling the vial rack on to start heating too.)
Once the samples are cool, you come back to the hood and you gently and carefully lift each one up to eye level while wearing your safety specs with the hood sash in between your hands and your face[1]. Rotate the beaker slowly: you're looking for any weird light refraction effects flagging up that you do in fact have drops of condensed HF+HNO3 in the threads. Any that look dodgy, set down in a distinct group from the ones that are Basically Fine.
It is now time to start uncapping the vials, very slowly and carefully. You've already established whether or not there's condensation in the threads; you now take another Kimwipe, fold it up, wrap it around the vial, and very gently tap it against the worksurface, in order to get condensation drops from the inside of the lid down into the main body of liquid. They contain tasty tasty sample, you see, and while ordinarily you'd just check the cap was on tight and then invert the vial to make sure you'd picked up all the drops, this is... not... something... you do with HF, just no, please don't, it's a bad idea.
And now it's time to take the lid off and then, even more gingerly, still using the Kimwipe as a bonus barrier between you and the vial's outards, lift it back onto the hotplate and drop it into a well on the rack, and balance its lid in the adjacent well. You do this for all of them, being particularly careful of any with HF condensation in the threads, once again checking both your hands and your Safety Tissue after every vial for any evidence of Wayward Drops.
And then you breathe a sigh of relief and go do something else for two and a half hours, or longer if you haven't managed to requisition one of the appropriate vial racks. (The thing the vial rack does is provide insulation and steady heat transfer most of the way up the vials, rather than heating them only from the bottom and letting airflow around the outsides cool them down rapidly from there. This means you evaporate faster, which is Convenient.)
What's going on at this point is that the HF has reacted with the silica, the SiO2 in your rock (for my basalts, typically around 50% by weight), to form silicon fluorides. It's quite difficult to break up SiO2, which is why we use HF at all (for digesting rocks; for tricking rocks into thinking via the magic of electricity), and is in turn why we have to store it in Teflon bottles (if you store it in quartz it will just eat its containment), but while the fluorides are easier to get rid of than silica they're still not super willing to budge. In particular, they aren't soluble in the reagents I need to use later on in this process, so now I need to to evaporate them off to get rid of (1) them and (2) all the remaining HF. I further want to do the initial evaporation relatively gently: the aim is to get the samples to the point where they're almost but, crucially, not quite dry. We call this the "gel stage", because it's sort of weird and lustrous and viscous and oozy, which is how you can tell you've got it Just Right. (If you're digesting a carbonatite rather than a basalt it's also a fascinating delicate shade of purple! Normally it is not purple, it's just sort of grumpy off-white.) Again: the fluorides you're attempting to get rid of aren't actually very soluble, so you don't want to dry them out completely, so you wait til they're Almost But Not Quite There and then... you redilute them with some more concentrated nitric and crank the temperature up to 180°C.
You may now do the tiny victory dance of NO MORE HF NO MORE HF NO MOOOOOOOOORE H FFFFFFFFF TIL NEXT TIIIIIIIIIME, and also the Ceremonial Disposal Of Your Outer Gloves With Great Relief.
You gotta add more conc nitric to this party at least another two times, about a third of a millilitre at a go, and then you start letting things dry all the way down and eyeballing them. If they're Not Cooked Yet they'll be stubbornly white(ish); if they're Ready For The Next Stage they'll have charming crinkly crispy brown edges. It's not actually a Maillard reaction but it looks enough like one to amuse me.
Your next problem is that this is a whole heckin' lot of Solid Material (by which I mean "we're now looking at about, ooh, 50mg"), and it's been thoroughly saturated in nitric acid, which is suboptimal given that we actually want it to end up in hydrochloric acid without detouring via aqua regia, "water of kings", so called because it will quite cheerfully dissolve lumps of actual gold.
It's... not as nasty as HF? It's still not actually something you want to piss around with if you don't need to.
So now what you do is you take the temperature right back down to 120°C, you whack 4ml of 6M HCl in each of your sample beakers, and you set them back on the hotplate - open - and let it very gently evaporate again, to make absolutely certain that insofar as there's any liquid hanging around in your sample once it Looks Dry, it's HCl not HNO3. In practice this takes long enough that I normally set it going overnight so I can come back to it in the morning; I think I have once or twice managed "hanging around until it's done" and it was so tedious and took so long that I have by-and-large given up on it, especially now my commute's as much longer as it is.
When you show up the next morning you have... literally about ten minutes' work to do. Each sample -- now dry -- gets another 2ml of 6M HCl, but this time you put the lid back on tight, tidy away the vial rack for someone else to use, and pop them back on the hotplate overnight. What we're after now is letting it get nice and soupy again: we want all the solids to dissolve properly in the acid, this time, so we don't have any misery chonks left to clog things up down the line.
So you do your ten minutes' work and then you find something else to do, and the next day you come in again and you add 10ml of MQ (ultra-pure) water to everything, cap it up again, and stick it back on the hotplate again, still at 120°C. This step brings the acid concentration down from 6M to 1M, which is where I want it, and makes absolutely certain that everything's really and truly properly dissolved with no remaining solids at all whatsoever...
... for The Column Chromatography, tune in next time, etc.
[1] In my very first term a labmate managed to get hot HNO3 + HF on their face in a feat of stunning incompetence that should never have happened. Just. Don't lift a hot beaker up above your head outside of the hood without a sash to protect you and then shake it, w h a t.
Which means that I return to twelve very small pressure cookers of rock soup, not to be confused with stone soup.
The first step is to lay out a bunch more Kimwipes inside the hood. The second is to, double-gloved, gingerly remove the vials from the hotplate and put them onto the Kimwipes. Again, you want to check your hands every ten seconds or so: although you can close the screw-cap vials pretty tightly, there's always a chance that you'll wind up with some of your hot acid mixture condensing around the cap and gradually working its way down the threads, all the better to drip on you. Which you don't want.
And you especially don't want that happening while it's still hanging out at 140°C, so having gently placed it down upon a piece of expensive glorified tissue, you leave it 20 minutes to cool down while you get on with other bits and bobs. (It is in the nature of the beast that there is almost always something else to be doing, and usually it's beaker cleaning, but now is also the point at which you increase the hotplate temperature to 150°C for the next step, and ideally sling the vial rack on to start heating too.)
Once the samples are cool, you come back to the hood and you gently and carefully lift each one up to eye level while wearing your safety specs with the hood sash in between your hands and your face[1]. Rotate the beaker slowly: you're looking for any weird light refraction effects flagging up that you do in fact have drops of condensed HF+HNO3 in the threads. Any that look dodgy, set down in a distinct group from the ones that are Basically Fine.
It is now time to start uncapping the vials, very slowly and carefully. You've already established whether or not there's condensation in the threads; you now take another Kimwipe, fold it up, wrap it around the vial, and very gently tap it against the worksurface, in order to get condensation drops from the inside of the lid down into the main body of liquid. They contain tasty tasty sample, you see, and while ordinarily you'd just check the cap was on tight and then invert the vial to make sure you'd picked up all the drops, this is... not... something... you do with HF, just no, please don't, it's a bad idea.
And now it's time to take the lid off and then, even more gingerly, still using the Kimwipe as a bonus barrier between you and the vial's outards, lift it back onto the hotplate and drop it into a well on the rack, and balance its lid in the adjacent well. You do this for all of them, being particularly careful of any with HF condensation in the threads, once again checking both your hands and your Safety Tissue after every vial for any evidence of Wayward Drops.
And then you breathe a sigh of relief and go do something else for two and a half hours, or longer if you haven't managed to requisition one of the appropriate vial racks. (The thing the vial rack does is provide insulation and steady heat transfer most of the way up the vials, rather than heating them only from the bottom and letting airflow around the outsides cool them down rapidly from there. This means you evaporate faster, which is Convenient.)
What's going on at this point is that the HF has reacted with the silica, the SiO2 in your rock (for my basalts, typically around 50% by weight), to form silicon fluorides. It's quite difficult to break up SiO2, which is why we use HF at all (for digesting rocks; for tricking rocks into thinking via the magic of electricity), and is in turn why we have to store it in Teflon bottles (if you store it in quartz it will just eat its containment), but while the fluorides are easier to get rid of than silica they're still not super willing to budge. In particular, they aren't soluble in the reagents I need to use later on in this process, so now I need to to evaporate them off to get rid of (1) them and (2) all the remaining HF. I further want to do the initial evaporation relatively gently: the aim is to get the samples to the point where they're almost but, crucially, not quite dry. We call this the "gel stage", because it's sort of weird and lustrous and viscous and oozy, which is how you can tell you've got it Just Right. (If you're digesting a carbonatite rather than a basalt it's also a fascinating delicate shade of purple! Normally it is not purple, it's just sort of grumpy off-white.) Again: the fluorides you're attempting to get rid of aren't actually very soluble, so you don't want to dry them out completely, so you wait til they're Almost But Not Quite There and then... you redilute them with some more concentrated nitric and crank the temperature up to 180°C.
You may now do the tiny victory dance of NO MORE HF NO MORE HF NO MOOOOOOOOORE H FFFFFFFFF TIL NEXT TIIIIIIIIIME, and also the Ceremonial Disposal Of Your Outer Gloves With Great Relief.
You gotta add more conc nitric to this party at least another two times, about a third of a millilitre at a go, and then you start letting things dry all the way down and eyeballing them. If they're Not Cooked Yet they'll be stubbornly white(ish); if they're Ready For The Next Stage they'll have charming crinkly crispy brown edges. It's not actually a Maillard reaction but it looks enough like one to amuse me.
Your next problem is that this is a whole heckin' lot of Solid Material (by which I mean "we're now looking at about, ooh, 50mg"), and it's been thoroughly saturated in nitric acid, which is suboptimal given that we actually want it to end up in hydrochloric acid without detouring via aqua regia, "water of kings", so called because it will quite cheerfully dissolve lumps of actual gold.
It's... not as nasty as HF? It's still not actually something you want to piss around with if you don't need to.
So now what you do is you take the temperature right back down to 120°C, you whack 4ml of 6M HCl in each of your sample beakers, and you set them back on the hotplate - open - and let it very gently evaporate again, to make absolutely certain that insofar as there's any liquid hanging around in your sample once it Looks Dry, it's HCl not HNO3. In practice this takes long enough that I normally set it going overnight so I can come back to it in the morning; I think I have once or twice managed "hanging around until it's done" and it was so tedious and took so long that I have by-and-large given up on it, especially now my commute's as much longer as it is.
When you show up the next morning you have... literally about ten minutes' work to do. Each sample -- now dry -- gets another 2ml of 6M HCl, but this time you put the lid back on tight, tidy away the vial rack for someone else to use, and pop them back on the hotplate overnight. What we're after now is letting it get nice and soupy again: we want all the solids to dissolve properly in the acid, this time, so we don't have any misery chonks left to clog things up down the line.
So you do your ten minutes' work and then you find something else to do, and the next day you come in again and you add 10ml of MQ (ultra-pure) water to everything, cap it up again, and stick it back on the hotplate again, still at 120°C. This step brings the acid concentration down from 6M to 1M, which is where I want it, and makes absolutely certain that everything's really and truly properly dissolved with no remaining solids at all whatsoever...
... for The Column Chromatography, tune in next time, etc.
[1] In my very first term a labmate managed to get hot HNO3 + HF on their face in a feat of stunning incompetence that should never have happened. Just. Don't lift a hot beaker up above your head outside of the hood without a sash to protect you and then shake it, w h a t.
(no subject)
Date: 2019-09-25 09:24 pm (UTC)w h a t. that's -- I don't even. W H A T.
(no subject)
Date: 2019-09-25 10:53 pm (UTC)(they then tried to leave A&E before having their blood calcium levels checked but THANKFULLY our lab manager stopped them. I am all Arch Amusement that when the steps that had been taken to get human to hospital were described in an emergency lab meeting, my response was "okay well you should have done xyz". PIs were all "well we're going to talk to the hospital and work out a better action plan for next time". PIs came back next week and said "... we've talked to the hospital, and if this ever happens again we'll do xyz.")
(no subject)
Date: 2019-09-26 08:04 am (UTC)(no subject)
Date: 2019-09-26 11:19 am (UTC)0. Do not at any point stop the calcium gluconate treatment.
1. Call 999. If they say an ambulance will be 3 hours, insist it is a life-threatening emergency and they need to Talk To A Burns Specialist. Try not to take a taxi, but if you can't convince despatch that this is actually a bit more urgent than "an acid burn" Do That I Guess.
2. When you show up at the hospital, again emphasise that this is not a common or garden acid burn. Ideally, have the MSDS on you.
2a. Emphasise how concentrated it is (they prefer percentages to molarity).
2b. Emphasise that it's potentially fatal.
2c. Emphasise that it requires the specific attention of a consultant burns specialist. (Ideally you know who your local burns specialist is and can insist on them by name.)
3. Do not let the patient leave until blood calcium levels have been checked and ideally, at some point while they're rustling up the consultant, emphasise that blood calcium levels are critical here (because the thing HF does is scavenge up all the calcium in your bloodstream, such that your electrolytes are wrong, such that your heart stops. Among other things.)
Broadly.
What actually happened was they ended up getting a taxi, and then they sat around in A&E for ages because it was just "oh I guess you spilled? some acid on yourself?" not "THIS PERSON MIGHT DIE ANY MOMENT", because it took A While to get hold of the appropriate burns specialist, who promptly went HOLY FUCK WHAT. Just. The really key point is not being nice and polite and I'm Sure They Know Best when, in fact, most hospitals will have no idea what an HF is because why would they.
(no subject)
Date: 2019-09-26 09:23 pm (UTC)Death by HF was on ER once. I was 12; it scared me stupid.
(no subject)
Date: 2019-09-27 04:45 am (UTC)(no subject)
Date: 2019-09-30 03:29 pm (UTC)(no subject)
Date: 2019-09-30 03:31 pm (UTC)(no subject)
Date: 2019-09-25 09:42 pm (UTC)(no subject)
Date: 2019-09-25 10:54 pm (UTC)(no subject)
Date: 2019-09-25 09:51 pm (UTC)(no subject)
Date: 2019-09-25 10:54 pm (UTC)(no subject)
Date: 2019-09-25 10:42 pm (UTC)And they aren't even very good at cleaning your glasses of smudges either.
(no subject)
Date: 2019-09-25 10:55 pm (UTC)(no subject)
Date: 2019-09-30 10:12 am (UTC)(no subject)
Date: 2019-09-25 10:43 pm (UTC)are precipitates an issue? or just that agitating the HF is a v v bad idea?
(no subject)
Date: 2019-09-25 10:58 pm (UTC)(I'd say "precipitates aren't really a concern with HF" but iN FACT we do have... a bottle... of the home-distilled stuff... very carefully wrapped up in a box... that is full of brown precipitate and we have no idea what they are or where they came from or WHY THEY'RE NOT DISSOLVING, and sooner or later we'll probably get around to evaporating this half-litre of 48M HF that is contaminated with something it doesn't dissolve but for the time being it's just an object of appalled curiosity...)
(no subject)
Date: 2019-09-26 03:11 am (UTC)(no subject)
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Date: 2019-09-26 12:59 am (UTC)(no subject)
Date: 2019-09-26 09:56 am (UTC)(no subject)
Date: 2019-09-26 01:58 am (UTC)Best description evar for semiconductors!
(no subject)
Date: 2019-09-26 02:00 am (UTC)(no subject)
Date: 2019-09-26 09:36 am (UTC)(no subject)
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Date: 2019-09-26 02:31 pm (UTC)(no subject)
Date: 2019-09-30 10:13 am (UTC)(no subject)
Date: 2019-09-30 03:33 pm (UTC)