Using Isotopes to Track Stuff Question

[justadream]

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When you use isotopes (e.g., Carbon-14, H-3, etc.) to track things, what exactly are you measuring?

I assume you would be measuring the decay of the substance (e.g., decay of Carbon-14 to Carbon-13). But is that true?

If so, how exactly is this "measured"?

 

[Teleologist]

You can use isotopes to test reaction mechanisms.

 

[justadream]

You can use isotopes to test reaction mechanisms.

Right, but what I am trying to understand is how exactly you measure the isotope (not the practical uses of isoptopes).

 

[Teleologist]

Right, but what I am trying to understand is how exactly you measure the isotope (not the practical uses of isoptopes).

Some isotopes are radioactive and this can be detected.

 

[justadream]

@Teleologist

Okay. So when you go about choosing which isotopes to use in biology, you usually choose to label something that is exclusively present in the target (e.g., label phosphorous to look at nucleic acids).

But is half-life ever a consideration? Some isotopes must decay a lot slower than others. I guess our instruments are good enough to overcome this?

 

[type12]

In the example you gave, the detection methods are usually by mass rather than decay.

 

[justadream]

@type12

Well isn't mass change because of decay (which is still related to half-life)?

 

[type12]

@type12

Well isn't mass change because of decay (which is still related to half-life)?

I don't see what the issue is. Even if the decay was that fast (which it won't be), if the masses are different, then... you've detected something that is not the same mass.

What do you want to do? Detect, or something else? There's a number of options we have. We can see if a current is generated when decay occurs or excite/react something with that radiation (ala ionizing radiation, most radioactive products are charged), but this depends on what you're seeking to do.

 

[Cawolf]

I believe that the actual process of measuring the radiolabeling is way out of the scope of this exam - and most undergrad science courses.

I think it is more important to know that it can happen, and if a passage presents the methods - how to interpret it.

I was searching through pubmed and there are a variety of ways to quantify the data - PET, dyes, gels, flow, mass, counts, etc.