Here’s another post for #RealTimeChem week (@RealTimeChem on Twitter). Today, we’re running isotopic analyses of the fossil teeth that we pretreated earlier.
Earlier this week, I weighed the samples. Well, I tried to weigh the samples.
In the lab, about to do some #realtimechem. So, naturally, fire alarm. twitter.com/paleololigo/st…
— Penny Higgins (@paleololigo) April 22, 2013
//platform.twitter.com/widgets.jsI made it back into the lab, and started again.
Back in the lab to weigh some samples. First, it puts the septa in the caps… #realtimechem twitter.com/paleololigo/st… — Penny Higgins (@paleololigo) April 22, 2013
Ready to start weighing. #realtimechem twitter.com/paleololigo/st… — Penny Higgins (@paleololigo) April 22, 2013
//platform.twitter.com/widgets.jsYou don’t need a lot to get an analysis, but these tiny samples are pushing the limits!
2.022 milligrams of tooth enamel = one good analysis. #realtimechem twitter.com/paleololigo/st…
— Penny Higgins (@paleololigo) April 22, 2013
Sometimes it’s hard to be sure you’ve actually weighed something.
It’s in there. Now repeat 31 more times. #realtimechem twitter.com/paleololigo/st…
— Penny Higgins (@paleololigo) April 22, 2013
//platform.twitter.com/widgets.jsIsotopic analysis is meaningless without laboratory standards of known isotopic value.
Samples are weighed. Now for the standards. Yes. We use chalkboard chalk as isotopic standards! #realtimechem twitter.com/paleololigo/st… — Penny Higgins (@paleololigo) April 22, 2013
Weighing standards can be frustrating, though.
Pure carbonate standards are a pain to weigh. They only need 200 micrograms. It’s in the weigh boat. #realtimechem twitter.com/paleololigo/st… — Penny Higgins (@paleololigo) April 22, 2013
You’ll just have to believe me when I say there’s 200 micrograms of carbonate in there… #realtimechem twitter.com/paleololigo/st…
— Penny Higgins (@paleololigo) April 22, 2013
Ready to go!
A full tray, ready to be analyzed tomorrow! #realtimechem twitter.com/paleololigo/st…
— Penny Higgins (@paleololigo) April 22, 2013
The next phase will be making the mass spectrometer happy, and go through the analytical steps. This isn’t something I have tweets for, but I do have pictures. (Go me!)
The first part is to get the mass spectrometer linear. That means that it’ll give you the right isotopic value, no matter what gas pressure goes in. This is hard.
This involves turning the carbon dioxide regulator knob every 40 seconds for at least 20 minutes.
I usually get a little sword practice in while this is going on.
Once you’ve got the instrument running right, you can inject acid into your sample vials. The mass spectrometer can only measure gasses. Reacting carbonates and bioapatites with phosphoric acid causes carbon dioxide to be released, which can be measured.
You’ve got to get the needle in the right place to insert into the vials.
Once you’ve got all that set up, then you can just hit the ‘start’ button on the computer that controls the mass spectrometer. Then go home and have an adult beverage. As it should be.
Penny Higgins - Storyteller • Artist • Scientist 
So is each of those sample vials an overnight run? Or will the mass spectrometer step through and analyze all of them?
I wonder if a powder trickler might make weighing out your chalk calibration samples easier.
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Good questions.
Each vial takes about 15 minutes to analyze, so the whole set runs over night.
The biggest problem with the standards is static, to be honest. Next comes getting the weights to be 200 micrograms plus/minus 20 micrograms. Once you get good, the weighing goes really quickly.
The best way to make weighing anything easier is to pay a student to do it for you! 😉
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Students are probably the better solution. Powder tricklers are used to precisely measure gunpowder for loading into firearm cartridges. They’re usually static-free. Those that aren’t, well, they don’t last very long. (grin) “Precisely” in this case means to a tenth of a grain, which is about 6500 micrograms.
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