What Do I Even Do All Day: Part 1.0.1
Nov. 29th, 2019 09:42 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
kaberettI left something out of my first post on digestions.
I left it out because, up until three rounds of chemistry ago, I had had to do it all of once, and had promptly put it back out of mind.
The last three rounds of chemistry, however -- the digestions where I'm working toward a fairly tight deadline -- have all needed it, and so they've all taken a week longer, and I am so glad to be done.
Leaching is a step that takes place after weighing but before digestion. While obviously you do your best to collect your rocks to be nice and fresh and sparkly, i.e. with limited post-depositional accumulated grot, this is not always possible. If, for example, you are working with a pumice that's 14,000 years old, to pluck a number entirely out of the air with no reference whatsoever to any previous publications on these rocks.
Post-depositional alteration is a particular concern for thallium, because while some elements don't particularly care for water and will stay stubbornly put, Tl is something it's notably easy to remove (or add!) during weathering processes. What you're doing with leaching is attempting to remove any easily-shiftable surface grot from your powdered rock, so that the numbers you end up measuring relate only to stuff that is firmly locked up in crystal structures as opposed to having been smeared on (or in between) at some late stage.
The way this works is: you weigh your rocks, and then instead of going straight to digesting them in a mixture of concentrated HNO3 and HF, you put about 10ml of distilled 6M HCl in each of your beakers. This rock juice gets tightly capped, put in an ultrasonic bath for thirty minutes, then left well alone for at least another thirty minutes to let some of the heavier particulates sediment out again.
In the meantime, you prepare another set of vials: the same number as the number you're sonicating. You label them carefully. And then you gently and slowly and with a minimum of agitation transport your rock juice from the ultrasonic bath to a hood, and then you very carefully pipette the leachate -- the juice -- into a new clean beaker, one per sample.
The leachate goes on a hotplate, uncapped, at around 120°C. The residue (the juicy bits!) gets topped up with another ~10ml of ultrapure HCl, capped, and put back in the sonicator for another 20-30 minutes, followed by another 30 minute rest to recombobulate itself.
When you first add HCl to your rock powder, your solution pretty immediately turns a very bright yellow. This is iron chloride forming, from the iron that's just sort of floating around loose on... the surface of your rock particles. Which is convenient! Because the way you tell when you're done rinsing-and-repeating with HCl is when the leachate stops turning yellow: if even after ultrasonic agitation there's no more readily-available iron -- it's all tucked up safely in mineral structures -- such that your solution just looks like slightly murky water, then congratulations! You've probably sucked up all the readily-available surficial thallium, too! This has taken you some time, though: it takes 6-8 hours to evaporate ~20ml of HCl at 120°C, and you've probably rinsed your solids with 40-50ml, and you can only evaporate a maximum of 22ml in one go because that's how big your vials are, so by this point you've been wrangling tedious fiddly volumes of acid for two to three days, and you are cursing the fact that you want to measure the isotopic composition of the leachate as well as the residue, because if you didn't you could have just thrown it all down the sink and been done much quicker. Alas: I'm actually interested (I will get to why, eventually, promise) in whether I see the same isotope ratio in the leachate and the residue prepared from the same initial powder.
But the thing is, you now want to digest your residue and indeed your leachate in a standard HNO3-HF mix, but you don't want to add HCl to the mix. Which means that, once you've evaporated all sodding 50ml of HCl, you... get to rinse your residues twice more! With ultrapure water! The same whole ultrasonication-and-drawing-off-the-leachate dance! About 10ml each time again!
And because it's water you don't want to set the hotplate any higher than about 95°C, so: enjoy! it's going to take even longer to evaporate! have fun!!!
(You might also have noticed that "getting rid of a bunch of the thallium from the sample powder" means "there's less remaining thallium to measure", such that you need to digest a larger initial mass in order to get the same yield of thallium, which is relevant when it comes to measurement. Happily, the samples I'm working with all have very high initial thallium concentrations -- by which I mean, up to half of one part per million, my goodness -- so this doesn't force me to use such large powder masses that I physically can't fit enough acid in a standard 22ml beaker to carry out a complete digestion. If I need that much sample powder -- any much above 250mg, depending on the rock type -- I end up having to split it between multiple initial vials & a much larger initial volume in order to get it all into solution, which makes loading it on to the column take longer, and it all just becomes extremely Very really quite quickly.)
This afternoon I got my probably-last-ever batch of samples through the end of the leaching process and into HF. They'll stew over the weekend; next week I'll be finishing up the sample prep, and the week after that it's columns. And then, eventually, finally, with a bit of luck and a following wind, I'll manage to analyse the last two batches of rocks, and that'll be it: data collection done with, and the degree all over bar the shouting.
I left it out because, up until three rounds of chemistry ago, I had had to do it all of once, and had promptly put it back out of mind.
The last three rounds of chemistry, however -- the digestions where I'm working toward a fairly tight deadline -- have all needed it, and so they've all taken a week longer, and I am so glad to be done.
Leaching is a step that takes place after weighing but before digestion. While obviously you do your best to collect your rocks to be nice and fresh and sparkly, i.e. with limited post-depositional accumulated grot, this is not always possible. If, for example, you are working with a pumice that's 14,000 years old, to pluck a number entirely out of the air with no reference whatsoever to any previous publications on these rocks.
Post-depositional alteration is a particular concern for thallium, because while some elements don't particularly care for water and will stay stubbornly put, Tl is something it's notably easy to remove (or add!) during weathering processes. What you're doing with leaching is attempting to remove any easily-shiftable surface grot from your powdered rock, so that the numbers you end up measuring relate only to stuff that is firmly locked up in crystal structures as opposed to having been smeared on (or in between) at some late stage.
The way this works is: you weigh your rocks, and then instead of going straight to digesting them in a mixture of concentrated HNO3 and HF, you put about 10ml of distilled 6M HCl in each of your beakers. This rock juice gets tightly capped, put in an ultrasonic bath for thirty minutes, then left well alone for at least another thirty minutes to let some of the heavier particulates sediment out again.
In the meantime, you prepare another set of vials: the same number as the number you're sonicating. You label them carefully. And then you gently and slowly and with a minimum of agitation transport your rock juice from the ultrasonic bath to a hood, and then you very carefully pipette the leachate -- the juice -- into a new clean beaker, one per sample.
The leachate goes on a hotplate, uncapped, at around 120°C. The residue (the juicy bits!) gets topped up with another ~10ml of ultrapure HCl, capped, and put back in the sonicator for another 20-30 minutes, followed by another 30 minute rest to recombobulate itself.
When you first add HCl to your rock powder, your solution pretty immediately turns a very bright yellow. This is iron chloride forming, from the iron that's just sort of floating around loose on... the surface of your rock particles. Which is convenient! Because the way you tell when you're done rinsing-and-repeating with HCl is when the leachate stops turning yellow: if even after ultrasonic agitation there's no more readily-available iron -- it's all tucked up safely in mineral structures -- such that your solution just looks like slightly murky water, then congratulations! You've probably sucked up all the readily-available surficial thallium, too! This has taken you some time, though: it takes 6-8 hours to evaporate ~20ml of HCl at 120°C, and you've probably rinsed your solids with 40-50ml, and you can only evaporate a maximum of 22ml in one go because that's how big your vials are, so by this point you've been wrangling tedious fiddly volumes of acid for two to three days, and you are cursing the fact that you want to measure the isotopic composition of the leachate as well as the residue, because if you didn't you could have just thrown it all down the sink and been done much quicker. Alas: I'm actually interested (I will get to why, eventually, promise) in whether I see the same isotope ratio in the leachate and the residue prepared from the same initial powder.
But the thing is, you now want to digest your residue and indeed your leachate in a standard HNO3-HF mix, but you don't want to add HCl to the mix. Which means that, once you've evaporated all sodding 50ml of HCl, you... get to rinse your residues twice more! With ultrapure water! The same whole ultrasonication-and-drawing-off-the-leachate dance! About 10ml each time again!
And because it's water you don't want to set the hotplate any higher than about 95°C, so: enjoy! it's going to take even longer to evaporate! have fun!!!
(You might also have noticed that "getting rid of a bunch of the thallium from the sample powder" means "there's less remaining thallium to measure", such that you need to digest a larger initial mass in order to get the same yield of thallium, which is relevant when it comes to measurement. Happily, the samples I'm working with all have very high initial thallium concentrations -- by which I mean, up to half of one part per million, my goodness -- so this doesn't force me to use such large powder masses that I physically can't fit enough acid in a standard 22ml beaker to carry out a complete digestion. If I need that much sample powder -- any much above 250mg, depending on the rock type -- I end up having to split it between multiple initial vials & a much larger initial volume in order to get it all into solution, which makes loading it on to the column take longer, and it all just becomes extremely Very really quite quickly.)
This afternoon I got my probably-last-ever batch of samples through the end of the leaching process and into HF. They'll stew over the weekend; next week I'll be finishing up the sample prep, and the week after that it's columns. And then, eventually, finally, with a bit of luck and a following wind, I'll manage to analyse the last two batches of rocks, and that'll be it: data collection done with, and the degree all over bar the shouting.
(no subject)
Date: 2019-11-29 09:43 pm (UTC)... this is all very weird and I'm feeling slightly unmoored.
(no subject)
Date: 2019-11-29 09:52 pm (UTC)(no subject)
Date: 2019-11-29 10:12 pm (UTC)(no subject)
Date: 2019-11-30 05:49 am (UTC)(no subject)
Date: 2019-11-30 10:58 am (UTC)(no subject)
Date: 2019-11-30 03:48 pm (UTC)How are you going to celebrate? (I've been listening to Productivity Alchemy again, and Kevin Sonney is very big on celebrating one's successes.)
(no subject)
Date: 2019-11-30 04:39 pm (UTC)I went to IKEA on the way home last night, and in addition to the bedsheets I'd been planning on I got STACKING COOLING RACKS for the kitchen (and a 60p cinnamon bun).
Today I have been mostly experiencing the politics-induced crazy, but I'm up to 120/123 animal cards in Botanicula and I'm experimenting with learning to darn a sheet.
(no subject)
Date: 2019-12-02 03:01 pm (UTC)When I found the bandwidth to read all your What Do I Even Do All Day posts, I saw a thing from Wikipedia's aqua regia page:
[cn: there are nazis, but this is a story about someone getting the better of them]
"When Germany invaded Denmark in World War II, Hungarian chemist George de Hevesy dissolved the gold Nobel Prizes of German physicists Max von Laue (1914) and James Franck (1925) in aqua regia to prevent the Nazis from confiscating them. The German government had prohibited Germans from accepting or keeping any Nobel Prize after jailed peace activist Carl von Ossietzky had received the Nobel Peace Prize in 1935. De Hevesy placed the resulting solution on a shelf in his laboratory at the Niels Bohr Institute. It was subsequently ignored by the Nazis who thought the jar—one of perhaps hundreds on the shelving—contained common chemicals. After the war, de Hevesy returned to find the solution undisturbed and precipitated the gold out of the acid. The gold was returned to the Royal Swedish Academy of Sciences and the Nobel Foundation. They re-cast the medals and again presented them to Laue and Franck."
(no subject)
Date: 2019-12-02 09:18 pm (UTC)YES GOOD
(no subject)
Date: 2019-12-01 02:21 am (UTC)(no subject)
Date: 2019-11-29 10:04 pm (UTC)(no subject)
Date: 2019-11-30 02:48 am (UTC)(no subject)
Date: 2019-11-30 03:16 am (UTC)