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Topic: Radiochemistry questions?  (Read 3776 times)

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Offline ChinusGomes

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Radiochemistry questions?
« on: October 09, 2019, 07:54:29 AM »
I am an organic chemist transferring to radiochemistry. I have some basic radiochemistry questions I seem to not be able to answer from books and unfortunately the collaborators on that side are kind of MIA at the moment. If there is anyone with experience in that field I would love to get in touch!
When looking at the incorporation of [18F]-fluoride into organic molecules, they give the amount of [18F] as GBq, which fine I can convert to moles easily. But then on their large scale preparation, they give a specific activity of the radiofluorinated compounds. My understanding is that if SA is not maximal, it comes from having some non-radioactive nuclide in there ([19F] in this case), but then where does it come from as they use non-carrier added [18F]? Please feel free to hit me with facts if I am completely mistaken.

In the SI, they detail the calculation of the specific activity. I do not understand the units of the graph used though, how do you go from mAu*min to Becquerels?!

Offline chenbeier

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Re: Radiochemistry questions?
« Reply #1 on: October 09, 2019, 08:54:07 AM »
What is mAU*min ? Milli absorbance unit  times minutes.?? Bequerel is acivity per second.

Offline mjc123

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Re: Radiochemistry questions?
« Reply #2 on: October 09, 2019, 09:58:59 AM »
What is the graph? Can you post a picture?

mAU*min sounds like the area of a chromatography peak. If you have a calibration curve (compound-specific and instrument-specific) of mAU*min vs. moles injected, you can work out how many moles of sample were injected (and, with the injection volume, the concentration).

The activity A of a sample in Becqerel is given by A = nNA*ln2/t1/2
where n is the number of moles, NA the Avogadro constant, and t1/2 the half-life in seconds.
The specific activity would be A/m (per gram) or A/n (per mole).
If your sample mass is m g, and your injection contained mi g, and the peak area indicates ni moles in the injection, then your sample contains n = ni*m/mi moles of compound.

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