I am trying to characterize the release kinetics of a small molecule from alginate beads. The small molecule is very simple and very challenging to detect with methods other than mass spec . To avoid using MS since it is expensive, I am considering getting a radiolabeled version of it and detecting it. I'm deciding between a 14C version and a 3H version. No one in my lab has extensive experience with radioactivity and I am unsure of some things that might be obvious for people who work with it extensively. For instance, are you supposed to mix the radiolabeled version with the normal small molecule and, if so, how do you know how much to put in? I'm also wondering what the lower limit of detection for each would be and how to detect the concentration. I've read a bit about liquid scintillation counting but is that the only method or are there plate readers that work for radioactive substances. I'd appreciate any input on the topic as I feel a little lost. Thank you!
Liquid scintillation is likely the best way to go. Nevertheless, some chemicals do not work well in liquid scintillation. Talk to the LS department you intend to use.They can best tell you what is needed and how to prepare. Also, talk to radiation safety officer for your institution.
More information needed to answer your question.
Hi, Michael Kozma
There are limited methods for measuring tritium. This is because tritium does not emit gamma rays, but only low-energy beta rays of up to 18.6 keV. For this measurement, it is desirable to have contact between the sample and the scintillator. In other words, if the sample is in gaseous form, the gas should flow into the ionization chamber. Otherwise, as Joseph L Alvarez pointed out, you can use a liquid scintillation counter to measure it.
You can see a recent review on low energy beta measurements (open access)
- https://www.mdpi.com/2227-9040/8/4/106
Article Low Energy Beta Emitter Measurement: A Review
Carbon-14 has much higher energy (roughly x10) of beta-particles (electrons). It makes it much easier to detect (e.g. scintillator flash is much stronger). Also, the effective range (how long the electron travels before getting stuck) is much large for carbon-14: 50um vs 0.27um for Tritium. For that reason, tritium can only be effectively detected by mixing the compound into liquid scintillator on close to or molecular level. The carbon-14 still can be detected if substance is spread as microdroplets or thin layer on top of the detector (e.g. solid plastic scintillator coupled to PMT) - it can be done by e.g. inkjet printing of the sample By Polypico machine.
Label with 14C and use liquid scintilation counter for measurement. Samples should be in liquid form.
Hi,
when you use radiolabeled solution you can use the Liquid Scintillation counting to detect the signal, and this method is very good and with high-quality skills, such as very good sensibility, in some case very easy sample treatment...
In my opinion, you should consider:
- H-3 or C-14 or other radionuclides (such as Iodine, 125, 131 or 129, Luthetium 177): what is the chemical behavior that you needed? H, C, or other, what is the best solution for your molecula?
- Kind of emission from radionuclides: beta? Alpha? EC or x/Gamma? You speak about H-3 and C-14, beta emitters, with respectively low energy and medium-high energy. LSC is the best to measure beta emitters in liquid samples.
- How much Bq do you need? Before starting with the measure with LSC, you should know the MDA that you can have with the blank sample. When you have this information, you can know how much Bq of radiolabeled solution use, or how much cost the experiment.
Be careful, there are a lot of LSC's instruments...but they are not cheap.
Maybe here you could find some info:
te_1528_web.pdf (iaea.org)
or
46135125.pdf (iaea.org)
Best Regards
Mattia
Thank you all for your input! I feel I have a better understanding of how these experiments work now. I'll be planning out this experiment in the near future so I look forward to trying it out.
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