What Do I Even Do All Day: Part 3
Oct. 10th, 2019 10:51 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
kaberettHaving made rock stew, the next step is to delicately extract a single ingredient from it and then throw the rest away: enter column chromatography.
[Two Perspex racks containing quartz columns. Screw-top Teflon vials containing a yellow liquid are also standing on the racks. Also featuring a small bottle of red liquid, various beakers and bottles, and an Eppendorf micropipette.]
This is basically the same principle as filtering water through sand or charcoal or a Brita filter to render it potable, only fancier, and instead of aiming to get the water with all the gunk -- the sodium and potassium and calcium and misc other Things -- removed, and left on the filter, I'm aiming to end up with just my thallium.
The way this works is: the columns in the photograph above are my Big Columns, long quartz cylinders with a little bit of a pinch at the bottom and a much wider cup-shaped reservoir at the top. On top of the pinch is a bed of quartz wool; on top of the quartz wool is approximately a millilitre of anionic exchange resin. This resin is positively charged, so negatively charged ions -- atoms or molecules plus some bonus electrons -- will stick to it, to varying degrees. In general, column chromatography relies on those varying degrees being consistent and repeatable -- so that, for example, you know that all of the element (or molecule, or...) you care about will wash off in a certain interval of eluent, such that if you collect everything from your fifth millilitre of eluent to, say, your eighth, you'll get all of your element-of-interest and relatively little of anything else, because Science. (If you want me to explain more about how this bit works, I can explain it more! Please ask.)
Happily for me, thallium chemistry is even simpler than that: it's got two available oxidation states (i.e. how many electrons it has), and in one of them it'll stick to the resin we use -- AG 1-X8 -- incredibly stubbornly even while nothing else does, and in the other it just cheerfully washes right off. We call this "on-off" chemistry: no need to worry about the intervals, just about the oxidation state, and that's pretty easy to manipulate with the chemicals that you're putting through the columns.
Less happily for me, the chemicals in question are... slightly awkward. The thing that works best to keep thallium stuck to the resin is having a bunch of bromide ions around in the presence of acid: the H+ ions in the acid will happily scavenge electrons from thallium, giving you Tl3+, which is a cation; this then complexes with Br- to give you a compound that, in spite of the fact that the thallium itself is carrying a positive charge, will stick to the resin that is also positively charged. To get these bromide ions, I have a ~125ml Teflon bottle stashed in the hood containing ~15ml of liquid bromine (one of the only two elements that's liquid at room temperature and pressure!) and, floating on top of it, because it is Much Less Dense, a bunch of MQ water: this gives me water that's saturated with bromine, which I can then add to my other acids, and indeed to my samples themselves: either the night before or the morning of, the samples (in their 12ml of 1M HCl) get 400µl of bromine-water each, and left to oxidise for at least three hours.
But this is not, in fact, the most tedious reagent I have to use.
The most tedious reagent is the solution of SO2 in weak hydrochloric acid.
The reason it's the most tedious reagent is that it needs making up fresh every single time: as it hangs around the SO2 gradually reacts with the acid it's dissolved in to give you H2SO4, which unfortunately does not do what I need it to, in terms of the chemistry, so once it's been hanging around for a week it needs chucked.
Consequently, a few days before any round of columns ever, I get to spend some Quality Time with a cylinder of compressed SO2 (yes it's metal, yes I take it into the metal-free clean lab, yes this makes everyone else even more unhappy than I am about it), two bottles of 0.1M HCl, a set of scales, and a lot of tubes. (I need a solution that's 5% SO2 by weight; depending on how cooperative everything's feeling this takes between 20 and 40 minutes to achieve via the medium of Patient Bubbling With Some Bonus Swirl.)
... so, right, having done all that we get to the point of setting up the photograph you see above. At the beginning of every round of chemistry, I clean the racks with MQ (particularly scrubbing around the holes the column stems pass through, using a Kimwipe); I wipe down the interior of the laminar flow hood thoroughly with more MQ and more Kimwipes; and then I rinse the columns through three times, with 1M HCl and 1M HNO3 and, finally, MQ.
Actually loading the resin onto the column is... kind of inevitably messy. You take your squeeze bottle of 0.1M HCl, and your squeeze bottle of AG 1-X8 (200-400 mesh) in ~0.1M HCl, and then you dump a load of acid in a column and squeeze some resin in on top of it (the idea being that the resin gets to settle through liquid, which reduces the chances of Trapping An Air Bubble, which you really don't want to do, because if there's an air bubble all the liquid you subsequently put through the column has to squidge around its edges i.e. it's got a much narrower tube to travel through. This is what we call a bottleneck and it makes everything much slower and then you Never Leave This Basement Again and also, possibly, cry.
I mentioned up above that for the Big Columns we want a millilitre of resin. We work out how much a millilitre is by, back in the mists of time, pipetting one in with a pen clutched in our other hand and then swooping in to mark the volume as soon as we've done so: this is going to be at a different height for each column due to slightly different total lengths, different volumes of quartz wool, etc. So you mark this once, and then you do your best to forget about it, and on every subsequent occasion (at least until you have to change the quartz wool) you just squirt resin in up to the line, BUT this is always a matter of trial-and-error and going-back-and-doing-a-bit-more until you're reasonably happy with it. This part tends to take somewhere between twenty minutes and half an hour, depending on how fussy you are...
... and once you've loaded the resin (your clean resin, which you cleaned a big bottle of in the past) onto the column, It's Time To Clean The Resin Again In Situ.
Well. "Condition" the resin: only the first step is really cleaning, in that you take your painstakingly concocted tedious 0.1M HCl-5wt% SO2 and dump 11 resin volumes (RV) of it through the column (in an initial small batch of 1ml, and a subsequent large batch of 10ml), just to make absolutely certain that there is really truly definitely no thallium at all whatsoever hanging around before you get started.
Then you take another 11 RV of 0.1M HCl and slosh it in (again as a small initial lot to get the resin used to the idea, followed by the rest of it in one big whack): we've made sure there isn't any thallium, but now we want to make sure there isn't any SO2 still hanging around either, because if there is it might stop the thallium we do care about and want -- the sample thallium -- from sticking to the resin as effectively as it ought.
So we've rinsed the resin with SO2 to make sure it's free of thallium before we get started, we've rinsed it again to make sure there isn't any remaining SO2, and as the final conditioning step we introduce it to the general concept of the acid the sample's in: 1M HCl, with some bromine kicking around, so that when we actually add the sample it's entering a hospitable and welcoming environment that's already been set up just so: the carrier acid doesn't have to rearrange the metaphorical furniture to be comfortable (risking some of the thallium deciding it doesn't like it here and doesn't want to stop), so the bits of the sample I care about can just settle in.
From getting into lab to loading my sample onto the column, for the big columns, takes about three hours. It's not just that it takes a while for the liquid to percolate through the resin: it's also that it's important to avoid disturbing the top of the resin bed as much as possible when introducing new acid, because the resin's designed to work by sitting still and having acid wash over and past it, not by just sort of floating around in the liquid portion of the column on its own merry little adventure. Stuff doesn't stick as well, or for that matter wash through as well, without the gravity pushing stuff through. (I'm quite sleepy and probably need to revisit this simile in the morning, but -- it's kind of like trying to fish a fragment of something untoward out of a bowl of liquid and having it keep running away from you, compared with straining the liquid through a sieve.) This means that at least the first 2ml of each acid gets dropped in slowly and delicately and gently from a pipette, though I do thank goodness then get to fill the reservoir from a measuring cylinder, rather than having to do everything the long slow way.
There's then a convenient break of half an hour or so while the columns are draining during which the most sensible thing for me to do is Acquire And Consume Lunch, so this point is generally where that happens.
[Another photograph of a laminar flow hood, from further back: this time a wooden stool is visible, as are two narrow sets of plastic drawers being used as tables. On the drawers to the left of the stool is a lab book, pen, small IKEA clock in shades of blue, box of Kimwipes, and box of Eppendorf 1ml pipette tips. On the right are some bottles of acid. In the hood, the columns contain a yellow liquid and the top of the resin bed is red. There is a new set of empty, differently labelled Teflon vials on the rack.]
The next chunk of work is aimed at washing everything that isn't thallium through the resin and into the waste beakers (in principle I could collect it for further separation but in practice I don't care). There are three steps to this: (1) get the columns used to the idea of switching over to HNO3, while making sure the thallium stays sticky, by rinsing through 18ml of 0.5M HNO3-3% Br2 (as 1ml/1ml/1ml/5ml/10ml); (2) using a more concentrated HNO3 solution (2M HNO3-3% Br2) to get rid of everything that isn't thallium (1ml/1ml/4ml/10ml); and (3) getting the resin used to the idea of hydrochloric again (0.1M HCl-1% Br2, 1ml/1ml/4ml/10ml). Each of these bromine solutions is made up in a set of dedicated low-density polyethylene Br2-mix bottles that never get used for anything but these reagents; the day before I start column chemistry I bung them all on a hotplate at ~95°C in 4M HNO3 to make sure they're good and clean, and then prior to making up each reagent flux them for a little while in either more 4M HNO3 or a wee bit of 1M HCl, depending on what's going into them next. (The idea of this is that if there's any grot on the bottle that might dissolve in the acid you want to use next, it'll all come out in hot acid of a higher concentration than the cold acid that actually constitutes your reagent, so you won't get contamination of the thing you care about.)
At this stage, the top of the resin bed is red-to-orange because of all the bromine that's sticking to it (left entirely to its own devices it's yellow). Once the last of the 0.1M HCl-1% Br2 has drained through, the waste beakers get emptied and I put some new Teflon vials under the columns to collect the thallium fraction. This gets washed through in another 16 RV of the 0.1M HCl-5wt% SO2, as 1ml/1ml/1ml/3ml/9ml/1ml, done gradually and piecewise to make absolutely certain that we coax all the thallium back off the resin; by the time that's finished running through, if I've been working efficiently and the heating's been working it's getting on for 6pm, assuming at ~8am start.
I am now faced with a choice between Going The Fuck Home and Getting It All Ready For The Next Stage Now To Save Myself A Commute In Future. I've got 16ml of acid in a bunch of beakers; it contains sulphur, so it's a bit sticky and miserable; and I need to get rid of all of that sulphur again, or at least as much of it as is possible. To get this done, the vials all go back onto a hotplate, in a rack, uncapped, at 200°C -- and, if I'm hanging around for the evening, I go and get dinner. (Sometimes with A; this Tuesday just gone, when I took these photos,cesy came to hang out with me.) Depending on the hotplate I'm using, it takes 2-3 hours to dry the full volume down, which together with the commute adds up to a very long day, but once it's dry all I have left to do is add ~0.1ml of concentrated (~12M) HCl to each vial, let that dry down again, take them off the heat, add 1.5ml of 1M HCl and 60µl of bromine water, cap them, and tidy up (emptying waste beakers, throwing away disposable pipette tips, cleaning the resin out of the columns with MQ and giving the racks another clean, ...)
... and then I'm just about ready to do it all again, only this time in miniature.
[The Perspex racks containing the large quartz columns have been moved to the back of the hood and covered with Perspex lids. The hood now also contains a set of much smaller Perspex racks, with small shrink-fit Teflon columns. The reservoirs contain a yellow liquid. The pipette is on a rack at the side of the hood; in the centre is a small dropper bottle containing an orange acid-bromine mix. The Perspex rack has green paper tape affixed to its outside surface to make the tops of the Teflon columns easier to see.]
[Two Perspex racks containing quartz columns. Screw-top Teflon vials containing a yellow liquid are also standing on the racks. Also featuring a small bottle of red liquid, various beakers and bottles, and an Eppendorf micropipette.]
This is basically the same principle as filtering water through sand or charcoal or a Brita filter to render it potable, only fancier, and instead of aiming to get the water with all the gunk -- the sodium and potassium and calcium and misc other Things -- removed, and left on the filter, I'm aiming to end up with just my thallium.
The way this works is: the columns in the photograph above are my Big Columns, long quartz cylinders with a little bit of a pinch at the bottom and a much wider cup-shaped reservoir at the top. On top of the pinch is a bed of quartz wool; on top of the quartz wool is approximately a millilitre of anionic exchange resin. This resin is positively charged, so negatively charged ions -- atoms or molecules plus some bonus electrons -- will stick to it, to varying degrees. In general, column chromatography relies on those varying degrees being consistent and repeatable -- so that, for example, you know that all of the element (or molecule, or...) you care about will wash off in a certain interval of eluent, such that if you collect everything from your fifth millilitre of eluent to, say, your eighth, you'll get all of your element-of-interest and relatively little of anything else, because Science. (If you want me to explain more about how this bit works, I can explain it more! Please ask.)
Happily for me, thallium chemistry is even simpler than that: it's got two available oxidation states (i.e. how many electrons it has), and in one of them it'll stick to the resin we use -- AG 1-X8 -- incredibly stubbornly even while nothing else does, and in the other it just cheerfully washes right off. We call this "on-off" chemistry: no need to worry about the intervals, just about the oxidation state, and that's pretty easy to manipulate with the chemicals that you're putting through the columns.
Less happily for me, the chemicals in question are... slightly awkward. The thing that works best to keep thallium stuck to the resin is having a bunch of bromide ions around in the presence of acid: the H+ ions in the acid will happily scavenge electrons from thallium, giving you Tl3+, which is a cation; this then complexes with Br- to give you a compound that, in spite of the fact that the thallium itself is carrying a positive charge, will stick to the resin that is also positively charged. To get these bromide ions, I have a ~125ml Teflon bottle stashed in the hood containing ~15ml of liquid bromine (one of the only two elements that's liquid at room temperature and pressure!) and, floating on top of it, because it is Much Less Dense, a bunch of MQ water: this gives me water that's saturated with bromine, which I can then add to my other acids, and indeed to my samples themselves: either the night before or the morning of, the samples (in their 12ml of 1M HCl) get 400µl of bromine-water each, and left to oxidise for at least three hours.
But this is not, in fact, the most tedious reagent I have to use.
The most tedious reagent is the solution of SO2 in weak hydrochloric acid.
The reason it's the most tedious reagent is that it needs making up fresh every single time: as it hangs around the SO2 gradually reacts with the acid it's dissolved in to give you H2SO4, which unfortunately does not do what I need it to, in terms of the chemistry, so once it's been hanging around for a week it needs chucked.
Consequently, a few days before any round of columns ever, I get to spend some Quality Time with a cylinder of compressed SO2 (yes it's metal, yes I take it into the metal-free clean lab, yes this makes everyone else even more unhappy than I am about it), two bottles of 0.1M HCl, a set of scales, and a lot of tubes. (I need a solution that's 5% SO2 by weight; depending on how cooperative everything's feeling this takes between 20 and 40 minutes to achieve via the medium of Patient Bubbling With Some Bonus Swirl.)
... so, right, having done all that we get to the point of setting up the photograph you see above. At the beginning of every round of chemistry, I clean the racks with MQ (particularly scrubbing around the holes the column stems pass through, using a Kimwipe); I wipe down the interior of the laminar flow hood thoroughly with more MQ and more Kimwipes; and then I rinse the columns through three times, with 1M HCl and 1M HNO3 and, finally, MQ.
Actually loading the resin onto the column is... kind of inevitably messy. You take your squeeze bottle of 0.1M HCl, and your squeeze bottle of AG 1-X8 (200-400 mesh) in ~0.1M HCl, and then you dump a load of acid in a column and squeeze some resin in on top of it (the idea being that the resin gets to settle through liquid, which reduces the chances of Trapping An Air Bubble, which you really don't want to do, because if there's an air bubble all the liquid you subsequently put through the column has to squidge around its edges i.e. it's got a much narrower tube to travel through. This is what we call a bottleneck and it makes everything much slower and then you Never Leave This Basement Again and also, possibly, cry.
I mentioned up above that for the Big Columns we want a millilitre of resin. We work out how much a millilitre is by, back in the mists of time, pipetting one in with a pen clutched in our other hand and then swooping in to mark the volume as soon as we've done so: this is going to be at a different height for each column due to slightly different total lengths, different volumes of quartz wool, etc. So you mark this once, and then you do your best to forget about it, and on every subsequent occasion (at least until you have to change the quartz wool) you just squirt resin in up to the line, BUT this is always a matter of trial-and-error and going-back-and-doing-a-bit-more until you're reasonably happy with it. This part tends to take somewhere between twenty minutes and half an hour, depending on how fussy you are...
... and once you've loaded the resin (your clean resin, which you cleaned a big bottle of in the past) onto the column, It's Time To Clean The Resin Again In Situ.
Well. "Condition" the resin: only the first step is really cleaning, in that you take your painstakingly concocted tedious 0.1M HCl-5wt% SO2 and dump 11 resin volumes (RV) of it through the column (in an initial small batch of 1ml, and a subsequent large batch of 10ml), just to make absolutely certain that there is really truly definitely no thallium at all whatsoever hanging around before you get started.
Then you take another 11 RV of 0.1M HCl and slosh it in (again as a small initial lot to get the resin used to the idea, followed by the rest of it in one big whack): we've made sure there isn't any thallium, but now we want to make sure there isn't any SO2 still hanging around either, because if there is it might stop the thallium we do care about and want -- the sample thallium -- from sticking to the resin as effectively as it ought.
So we've rinsed the resin with SO2 to make sure it's free of thallium before we get started, we've rinsed it again to make sure there isn't any remaining SO2, and as the final conditioning step we introduce it to the general concept of the acid the sample's in: 1M HCl, with some bromine kicking around, so that when we actually add the sample it's entering a hospitable and welcoming environment that's already been set up just so: the carrier acid doesn't have to rearrange the metaphorical furniture to be comfortable (risking some of the thallium deciding it doesn't like it here and doesn't want to stop), so the bits of the sample I care about can just settle in.
From getting into lab to loading my sample onto the column, for the big columns, takes about three hours. It's not just that it takes a while for the liquid to percolate through the resin: it's also that it's important to avoid disturbing the top of the resin bed as much as possible when introducing new acid, because the resin's designed to work by sitting still and having acid wash over and past it, not by just sort of floating around in the liquid portion of the column on its own merry little adventure. Stuff doesn't stick as well, or for that matter wash through as well, without the gravity pushing stuff through. (I'm quite sleepy and probably need to revisit this simile in the morning, but -- it's kind of like trying to fish a fragment of something untoward out of a bowl of liquid and having it keep running away from you, compared with straining the liquid through a sieve.) This means that at least the first 2ml of each acid gets dropped in slowly and delicately and gently from a pipette, though I do thank goodness then get to fill the reservoir from a measuring cylinder, rather than having to do everything the long slow way.
There's then a convenient break of half an hour or so while the columns are draining during which the most sensible thing for me to do is Acquire And Consume Lunch, so this point is generally where that happens.
[Another photograph of a laminar flow hood, from further back: this time a wooden stool is visible, as are two narrow sets of plastic drawers being used as tables. On the drawers to the left of the stool is a lab book, pen, small IKEA clock in shades of blue, box of Kimwipes, and box of Eppendorf 1ml pipette tips. On the right are some bottles of acid. In the hood, the columns contain a yellow liquid and the top of the resin bed is red. There is a new set of empty, differently labelled Teflon vials on the rack.]
The next chunk of work is aimed at washing everything that isn't thallium through the resin and into the waste beakers (in principle I could collect it for further separation but in practice I don't care). There are three steps to this: (1) get the columns used to the idea of switching over to HNO3, while making sure the thallium stays sticky, by rinsing through 18ml of 0.5M HNO3-3% Br2 (as 1ml/1ml/1ml/5ml/10ml); (2) using a more concentrated HNO3 solution (2M HNO3-3% Br2) to get rid of everything that isn't thallium (1ml/1ml/4ml/10ml); and (3) getting the resin used to the idea of hydrochloric again (0.1M HCl-1% Br2, 1ml/1ml/4ml/10ml). Each of these bromine solutions is made up in a set of dedicated low-density polyethylene Br2-mix bottles that never get used for anything but these reagents; the day before I start column chemistry I bung them all on a hotplate at ~95°C in 4M HNO3 to make sure they're good and clean, and then prior to making up each reagent flux them for a little while in either more 4M HNO3 or a wee bit of 1M HCl, depending on what's going into them next. (The idea of this is that if there's any grot on the bottle that might dissolve in the acid you want to use next, it'll all come out in hot acid of a higher concentration than the cold acid that actually constitutes your reagent, so you won't get contamination of the thing you care about.)
At this stage, the top of the resin bed is red-to-orange because of all the bromine that's sticking to it (left entirely to its own devices it's yellow). Once the last of the 0.1M HCl-1% Br2 has drained through, the waste beakers get emptied and I put some new Teflon vials under the columns to collect the thallium fraction. This gets washed through in another 16 RV of the 0.1M HCl-5wt% SO2, as 1ml/1ml/1ml/3ml/9ml/1ml, done gradually and piecewise to make absolutely certain that we coax all the thallium back off the resin; by the time that's finished running through, if I've been working efficiently and the heating's been working it's getting on for 6pm, assuming at ~8am start.
I am now faced with a choice between Going The Fuck Home and Getting It All Ready For The Next Stage Now To Save Myself A Commute In Future. I've got 16ml of acid in a bunch of beakers; it contains sulphur, so it's a bit sticky and miserable; and I need to get rid of all of that sulphur again, or at least as much of it as is possible. To get this done, the vials all go back onto a hotplate, in a rack, uncapped, at 200°C -- and, if I'm hanging around for the evening, I go and get dinner. (Sometimes with A; this Tuesday just gone, when I took these photos,
cesy came to hang out with me.) Depending on the hotplate I'm using, it takes 2-3 hours to dry the full volume down, which together with the commute adds up to a very long day, but once it's dry all I have left to do is add ~0.1ml of concentrated (~12M) HCl to each vial, let that dry down again, take them off the heat, add 1.5ml of 1M HCl and 60µl of bromine water, cap them, and tidy up (emptying waste beakers, throwing away disposable pipette tips, cleaning the resin out of the columns with MQ and giving the racks another clean, ...)... and then I'm just about ready to do it all again, only this time in miniature.
[The Perspex racks containing the large quartz columns have been moved to the back of the hood and covered with Perspex lids. The hood now also contains a set of much smaller Perspex racks, with small shrink-fit Teflon columns. The reservoirs contain a yellow liquid. The pipette is on a rack at the side of the hood; in the centre is a small dropper bottle containing an orange acid-bromine mix. The Perspex rack has green paper tape affixed to its outside surface to make the tops of the Teflon columns easier to see.]
(no subject)
Date: 2019-10-10 09:53 pm (UTC)(no subject)
Date: 2019-10-10 11:22 pm (UTC)(no subject)
Date: 2019-10-11 08:07 am (UTC)(no subject)
Date: 2019-10-11 08:09 am (UTC)commentspaaaaaaaaaaam
Date: 2019-10-11 08:10 am (UTC)Re: commentspaaaaaaaaaaam
Date: 2019-10-11 02:20 pm (UTC)Re: commentspaaaaaaaaaaam
Date: 2019-10-11 02:35 pm (UTC)Actually, for our purposes it's mostly that pigmentation is often achieved through addition of e.g. trace metals, and even when it's not adding pigment means you're adding another potential source of contamination! So we go for largely completely-unornamented, which mostly means clear or white(ish).
(I've then got yellow labels on the bottles for sulphur-containing compounds, red on the bromine, green on hydrochloric, black on nitric, blue on MQ, BRIGHT FUCKING ORANGE on HF and perchloric. I don't have to interact with silver-for-ethanol. :) )
Re: commentspaaaaaaaaaaam
Date: 2019-10-11 02:45 pm (UTC)I do like the idea of BRIGHT FUCKING ORANGE for acids that require you to be very careful with them.
(no subject)
Date: 2019-10-10 11:46 pm (UTC)Also, is it different between elements as to which part of the process will produce the purest, least-likely-to-be-contaminated sets of atoms? (Such that you would seek the first-fourth milliliters when looking for elements [Z], but the ninth-thirteenth for element [q]?
(no subject)
Date: 2019-10-11 08:12 am (UTC)And also: this is chemistry specifically designed for thallium. Chromatography for vanadium uses very very dilute HF in columns; procedures for other elements are similarly varied in terms of acids, reagents, etc, in addition to "where the stuff comes off, volumetrically". Designing new column chemistry to extract An Element (or extract it Better, or whatever) can easily add up to A Journal Paper and A Thesis Chapter both.
(no subject)
Date: 2019-10-11 02:19 pm (UTC)Are you specifically looking for radioisotopes when you're doing this kind of chemistry? Because I seem to recall at least one of thallium's is hot, and it seems like it would need extra procedure to make sure you're not dosing yourself with Hulk rays while you do the thing.
(no subject)
Date: 2019-10-11 02:32 pm (UTC)Ha, no, I'm working with stable Tl isotopes; all the radioactive ones are pretty short-lived and are no longer naturally occurring in our solar system. :)
(no subject)
Date: 2019-10-11 02:34 pm (UTC)(no subject)
Date: 2019-10-11 02:36 pm (UTC)(no subject)
Date: 2019-10-15 03:04 pm (UTC)(no subject)
Date: 2019-10-15 03:42 pm (UTC)(no subject)
Date: 2019-10-15 03:50 pm (UTC)(no subject)
Date: 2019-10-11 12:30 am (UTC)(no subject)
Date: 2019-10-11 12:44 am (UTC)(Icons related to chemistry are woefully lacking in this account; the only thing I could find that was even remotely relevant was this ball-and-stick model of citalopram. I should fix that.)
(no subject)
Date: 2019-10-11 08:12 am (UTC)(no subject)
Date: 2019-10-11 11:06 am (UTC)(no subject)
Date: 2019-10-11 08:12 am (UTC)(no subject)
Date: 2019-10-11 11:07 am (UTC)(no subject)
Date: 2019-10-11 02:46 am (UTC)(no subject)
Date: 2019-10-11 07:43 am (UTC)I've done it once over the six years of PhD, so no, not often! It does degrade gradually over time, but you can tell it needs replacing when you start getting bits of resin washed through as well.
(no subject)
Date: 2019-10-11 06:13 pm (UTC)Actinic lights would be seriously ouchie on this glassy setup. When you say quartz, do you mean actually someone mined a large pure quartz and cut those out of it? Because, wow.
(no subject)
Date: 2019-10-12 05:57 pm (UTC)(no subject)
Date: 2019-10-24 03:21 pm (UTC)IT IS A LOT OF SCIENCE YES. Which, thankfully, I didn't have to do; the original paper goes into more How We Worked It Out detail, but is also unsurprisingly paywalled (I'm happy to provide copies).
I've never actually had to develop A Column Chemistry so I can't go into all the tedious detail (at least from first-hand experience), but at least some of how you do this is trial-and-error: you take a very pure reference material (how did you purify it? I don't actually know, the reason this comment is so delayed is I fell down a rabbit-hole of "but how DO the NIST produce their single-element standards, anyway", and utterly failed to come up with the necessary/appropriate search strings), you load a known amount of it onto the column, and then you see Where It Comes Out (by collecting absolutely everything), relative to other standards, and how well you can isolate it, in how small a volume (because you gotta dry it down later), and of what.
Quartz: ha, no, this is just super-pure SiO2 glass with minimal impurities :)
(no subject)
Date: 2019-10-25 06:02 pm (UTC)Ah, gotcha! That is something similar to how I do a complex test. I explore the system, then sort of take its temperature, writing everything down - not just the bits that look important, but ALL of it, because you never know what sort of weird emergent behavior a software system under stress will produce - and only when I'm satisfied I have a grasp of how it works do I start trying to make it misbehave.
...how do you make a purification standard when you by definition do not have something pure enough to standardize it with is a pretzel I had not previously considered.
this is just super-pure SiO2 glass with minimal impurities :)
That makes much more sense.
(no subject)
Date: 2019-10-11 09:14 pm (UTC)(no subject)
Date: 2019-10-12 02:23 pm (UTC)This just reminds me why I didn't get on with lab experiments in science. I hope you got good data after allll that faff!
(no subject)
Date: 2019-10-12 02:50 pm (UTC)Don't get to find out for another two weeks! ISN'T IT FUN :-p
(no subject)
Date: 2019-10-13 10:44 am (UTC)Probably: I never attempted a prep or an assay as complex as that!
These days, my interest in chemistry is vicarious: I still read Derek Lowe's 'In the Pipeline' blog, and a project in a bank a while ago has left me knowing far too much about the economics of the pharmaceuticals industry and I still take an interest.
...So it's fascinating and entertaining to read *in detail* that someone I know is working at the lab bench, no matter how everyday it may seem to you.
(no subject)
Date: 2019-10-15 03:06 pm (UTC)