kaberett | What Do I Even Do All Day: Part 1

I realised over dinner the other week that even A has very little idea what my day-to-day work life looks like; I think I may have inadvertently given the impression that I shut myself up in a lab for a few days and emerge at the other end, slightly dazed, clutching SCIENCE.

Therefore, in the interests of demystifying all of this a bit, I'm going to... talk about lab processes a bit? Talk about lab processes a bit.

The brief overview is that I'm measuring the precise composition of a trace element -- thallium -- in a variety of volcanic rocks. Every gram of rock will contain somewhere between 10 and 600 nanograms of thallium, which I want to separate out so that I can (eventually) measure the precise ratio of its two stable isotopes, ²⁰⁵Tl and ²⁰³Tl, for reasons. This means I need to work in ultra-clean conditions, because I'm working with such tiny quantities of material. So, for example, basically everything takes place in a suite of clean rooms: laboratories with positive air pressure, i.e. air pressure deliberately greater than local atmospheric pressure, where the entire air volume of the room gets replaced with completely new thoroughly filtered air multiple times an hour.

Skipping over all of the details of how I decide which rocks to analyse, and also all of the preparatory beaker-cleaning, let's start with Digestion.

The first step is weighing out my sample. If I'm lucky I'll have a vague idea of how much thallium (my element-of-interest) the rock contains, which lets me work out how much I need to digest in order to have enough thallium I can measure its isotopic abundances usefully; if I'm less lucky I have to guess, based on what kind of rock it is and its abundance of other relevant elements (rocks that are high in potassium tend to also be high in thallium, for example, because thallium can sit in the same crystallographic sites in silicate mineral structures that potassium hangs out in).

By the time I get my hands on them, my samples are all finely-ground powders, generally grey, in a series of oversized labelled vials. All I gotta do is suit up, grab some clean beakers, and settle myself down in the isolated weighing room with the microbalance (so called because it measures to microgram precision & accuracy).

(A digression: "suiting up" in this context means swapping my horrid outdoor shoes for a pair of entirely enclosed white Crocs that live in lab, putting on my low-residue anti-static hooded lab coat, putting on a Buff or other headscarf to keep my hair off my face because No, swapping my glasses out for my prescription safety specs, washing my hands in purified water, and putting on appropriate gloves. The purpose of this exercise is for the most part to protect my samples from me, rather than to protect me from them & the chemicals I'm processing them in. "Beakers" means screw-top PFA (generic Teflon) vials, which have been washed in a series of acids, rinsed in ultra-pure "MQ" water, and dried.)

Depending on how many people are coming in and out of lab (opening and closing doors affects the air pressures, and I'm working at high enough precision that that's enough to unsettle the balance) and how fussy the scales are feeling anyway, weighing out a batch twelve samples will take me between an hour and two and a half hours. Of those twelve samples, one is a total procedural blank (it's an empty vial, I don't put any rocks in it, I just open it up to the atmosphere in lab & put it through all the other steps of the process with all the other chemicals, so I can tell how much background thallium there is in the process), one is a well-characterised reference material (that's been measured a bunch of times, so I can check I'm getting the right ratio of thallium isotopes out - if I don't, that means I can't trust any of my sample measurements either), and ten unknown samples. For each of these I open up the balance, stick the capped vial on it, close it up again (because the scales live in a tiny box, because otherwise the fluctuations in air pressure caused by me moving around would prevent it from ever settling down), wait for the number to stabilise, write it down, dump my powder into the vial, close it up again, and weigh it again - repeatedly - until the balance stabilises to the point of giving me two numbers within (in theory) about a microgram of each other.

Sometimes I have to resort to using the antistatic gun, because wee powders you're weighing into plastic get very excited about static electricity and that... fucks with your weighing. I'm not entirely convinced it does anything, but the placebo effect is a marvellous thing.

Having weighed my powder out, the next -- immediate -- step is to drop some concentrated (14M) in-house-distilled nitric acid on it. Generally about half a millilitre to a millilitre, once I've confirmed the weight, in order to get it all taken up in liquid so it doesn't just... sproing out everywhere when I open the lid back up to add the concentrated (~~48M~~48%/28M) in-house-distilled HF, because (1) I just weighed that, and (2) it makes a mess and is a potential contaminant.

Once I've got everything weighed up it's back out of the balance room and into the main lab, where with any luck (1) I've booked the flow hood I need to work in, and (2) someone else will be around to babysit, while I do The Thing With The HF.

Hydrofluoric acid is Not Your Friend. It's very useful for dissolving silica, which means you can't store it in glass bottles because it just... eats... them. It gets used to etch computer chips. And in geology, because most rocks are mostly SiO₂, and mostly you don't care about the silica, so you want to eat it all up and boil it off and generally get rid of it so that you can actually pay attention to anything else that's going on in your rock. It will kill you if you fuck up, you do need to know where absolutely every single drop goes, but it's basically "perfectly safe" in the sense that because it's so nasty the protocols for handling it are extremely thorough: I'd have to fuck up at least three different things to actually be at any risk of harm, so, I just don't do that, then. (This does mean I have to be very careful about resting on the days either side of handling HF, and about postponing if I'm not feeling steady enough, which is deeply frustrating when it happens, but there we go.)

I slosh (carefully! in extremely controlled fashion!) the HF onto the samples, I cap them very tightly, I stick them on a hotplate at 140°C, and I leave them to stew in their own juices for two days while I get on with the rest of my life. (You leave them at least 12 hours in order to actually get everything into solution; you don't leave them longer than 48, or at higher temperatures, because that increases the risk that you'll get your charming conc HF-conc HNO₃ mixture condensing into the threads of the screw-top vial such that it's Hassle to undo safely.)

Sometimes, though, as is the case for my current set of samples, there is a Bonus Step. The Bonus Step is cold leaching: if the rocks I'm looking at are particularly susceptible to post-depositional alteration, e.g. they got picked up from underwater or they're a pumice i.e. full of holes, because thallium's fairly fluid-mobile and fairly easy to shift around it's important to make sure that the thallium I'm measuring is actually from the rock itself rather than whatever crud got stuck to the outside between its being erupted and being collected. For samples where this is necessary, instead of adding conc nitric after weighing, I add weak hydrochloric, and then when I take it back to lab I dump some stronger (6M, in-house-distilled, you get the idea) HCl on it (whereupon it goes yellow, because iron chloride is yellow) and... stick it in an ultrasonic bath for thirty minutes. And then I leave it to settle for at least 15 minutes, and then I carefully draw off the leachate with a precision pipette and dump it in another clean beaker and set it evaporating down at around 120°C, and then I put some more HCl on the powder residue and ultrasonicate it again (for twenty minutes, this time); rinse and repeat until the leachate runs clear. Then I get to do it all again with two rounds of MQ, to clear the HCl out, and by the way this all generates a ridiculous volume of leachate to dry down, and then when I have finally got all that done & the leachate's also dried I... apply HNO₃ and HF, and follow the steps above.

I have been learning Several Things about sensible ways to organise my life around Letting The Bloody Leachate Evaporate Overnight. There is so much of it. So much. Cold-leaching is adding a solid week to sample prep time, and that's almost all because of how long it takes the leachate to dry.

NEXT TIME: getting ready to separate out my thallium fraction. BEAKER CLEANING IS VERY GLAMOROUS.

Flat | Top-Level Comments Only | Expand All

From:

jjhunter

I really enjoyed this lab processes post!

*waves pom-poms of encouragement*

From:

kaberett

<333

I am going to be finished in lab by the end of the year, possibly Forever, and I really enjoy it so Writing It Up While I Remember Any Of It is a thing, yes yes.

From:

ghoti

I am so glad there's someone else who thinks the anti-static gun is pretend. it's a rubber band!

From:

kaberett

IT IS SO FAKE.

From:

niqaeli

I made A Face at the 48M HF (also I had to stop and take a moment to go !!! at the 48M you were NOT KIDDING that it’s concentrated) because I DID have to survive two semesters of organic chemistry lab in addition to the two semesters of lecture in order to acquire my biology undergrad and that will give you a healthy respect for HF what with it being the thing we never used because because undergrads are not to be trusted with anything that nasty. :P

so I admit I was definitely reassured when the next thing explained was how your protocols for handling it are Very Thorough. ^^;

From:

kaberett

Ha! Okay, so, here's How We Handle HF.

Step zero: there's a beaker in the entrance hall that contains the calcium gluconate and Very Simple Instructions On What To Do And How To Use It, printed in big friendly letters on the assumption that if it's required people will be panicking. (Key points: apply calcium gluconate with included spatula WHILE WEARING VINYL GLOVES YOURSELF, DO NOT EXPOSE YOURSELF WHILE TREATING SOMEONE ELSE'S BURNS, leave for two minutes, rinse off under plenty of water, reapply, also here's the number to call to get an ambulance called and here's what you need to say to make the hospital take "it's an acid burn" appropriately seriously.)

The HF itself is stored in a Teflon bottle, with the lid wrapped in Parafilm, inside a clear clip-top plastic box as secondary containment.

Before getting it out of its cupboard, I need to prep the hood for HF work. This means (1) wiping it all down with MQ water, (2) laying out Kimwipes across a broad swath of the hood and making sure they're all completely dry i.e. I dried up properly after the wipe-down (they're special low-residue tissues, essentially, and mean that I'll be able to see if I've spilled any liquid), (3) filling up my waste beaker with half a litre of purified water, and (4) getting out all my transfer beakers and pipettes etc. This includes conditioning a pipette tip with MQ; for most stuff, you condition (i.e. draw up the max volume you're going to want and then dump it in the waste beaker) with the acid you'll be using, to make sure that any grot that's on the tip that'll come up in the acid you're using goes into waste instead of into your sample, but you Do Not want to be dumping that much conc HF out into wastewater, so you condition with ultrapure water instead. (Part of the reason this is okay is that the HF is also ultrapure - it's been distilled in-house, in a Teflon still - and part of it is that you're putting it on at the very beginning of the process, so you're not introducing any contamination you won't be able to get rid of later, for most elements.)

You categorically do not go any further than this unless there's someone else in lab who's agreed to do the first aid if you start screaming.

Once I've done that, usually while wearing a single layer of (nitrile) gloves, it's time to put a pair of vinyl gloves on over the top - double-gloves of different materials for More Protection. Then it's time to get the HF secondary containment out of its cupboard. Quick visual inspection to make sure there's no condensation inside the secondary containment, and then you can remove the bottle and place it as far back into the flow hood as you can comfortably & safely reach. Remove the Parafilm. With the sash down between you and the bottle, carefully rotate it to check there aren't any visible droplets on the outside of the neck. If there are, you want to be super fucking careful about opening it (probably wrapping another Kimwipe around the base of the neck, that you dump immediately into your big beaker of water once it's soaked the droplet up); if there aren't, you merely want to be Careful.

Open up the transfer beaker (it's a 120ml wide round beaker: acids go into dedicated transfer beakers to make pipetting them easier, safer, etc). Open up the HF bottle, pour About The Right Volume into your transfer beaker, cap the main bottle again right quick (because you want the largest volume of the stuff open for the shortest time possible), do a visual inspection of both the Kimwipes this has all happened on and also your hands. From this point on, any evidence of Escaped Drops Of ...Something you treat as though they're HF: working as quickly as is safe, pull everything up and dump it in the waste water to dilute it.

One at a time, move your sample beakers up close to the transfer beaker, open them, and pipette the HF over. You want to do this at a fairly slow and steady rate, watching where every single drop goes - you really, really want to avoid splashes, so you also (so far as possible) clear the last wee droplet from the pipette into the larger volume with the greater surface area (i.e. the transfer beaker) rather than into the sample beaker. After pipetting HF into each sample, you lay the pipette down carefully with its tip over the transfer beaker (usually by putting its main body down on top of a close transfer beaker for a different acid), you cap up your sample tightly and move it to one side, and you do a visual inspection of both the Kimwipes and your hands. (I do this by holding them up to my face, palms towards me, the other side of the sash, and slowly folding my fingers down to make fists, so I can inspect both sides.)

Generally I add HF to my total procedural blank last, because that means I can chuck however much HF I've got left in with it - at the very end, rather than pipetting partial volumes I pick the transfer beaker up and very carefully tip it into the sample beaker, with both hands on the HF transfer beaker. Again, you watch where Every Single Drop goes.

Once all the samples are tightly capped, the lid's gone back onto the transfer beaker, and the samples are all moved onto the hotplate, it's time to tidy up. Another strip of Parafilm gets cut and wrapped around the lid of the HF bottle (which you've checked is on tight); the bottle goes back into secondary containment; the secondary containment goes back into the cupboard; you check your gloves again. You rinse the pipette tip through with water from the waste beaker about three times, then drop it onto one of the Kimwipes, then wrap it up in your vinyl gloves as you take them off, and stick it in the bin. Waste water goes down the sink, the rest of the Kimwipes go in the bin, and then you wipe the hood down with MQ again.

In order to sustain a potentially dangerous exposure, something would have to go wrong with at least two of (1) wearing appropriate protective equipment, (2) prepping my workspace, (3) being sufficiently careful with handling the acid (e.g. not going "nah, too shaky today, it's tedious but this gets put off", only handling it inside the hood with the sash down as far as possible, etc), (4) watching where every drop goes, and (5) regular visual inspection of my hands and workspace. So: it's something to be careful with, it absolutely can kill you, but also it's fundamentally pretty easy to be safe. :)

only by balancing move

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