Mass Spectrometry: Understanding Boron Isotopes

[Chemist20]

Hello,

I'm now studying mass spectrometry. But there's something I don't get.

Imagine you have a compound with just one boron atom. This boron atom can me 10B or 11B. So, when you do mass spectrometry, you get two signals of different intensities depending on the natural abundance of each isotope. yes?

Well.. I don't get why if there's only one B there has two be two signals. I mean, either it is 10B or 11B. It's not like 20% of the boron is made of one isotope and 80% of the other right?

thanks!

 

[jtbell]

It's not like 20% of the boron is made of one isotope and 80% of the other right?

Why not? Any sample that you study with a mass spectrometer has many boron atoms in it.

 

[Chemist20]

Why not? Any sample that you study with a mass spectrometer has many boron atoms in it.

yeah, but I'm talking about there being just one boron

 

[Borek]

And for each atom you get a single signal at either 10 or 11 - but you never do test on a single atom, you use a sample containing zillions of atoms.

 

[jtbell]

Right, if you were able to send one boron atom through the spectrometer, or one molecule that contains a single boron atom, it would go either one way (into the "10B spot") or the other (into the "11B spot"), and you would get a single "spot" on the film or digital sensor.

But even a tiny real-world sample has many many atoms or molecules.

 

[Chemist20]

okey, so when it says 20% it doesn't mean that 20% of ONE boron atom is made of an isotope and 80% of another right? thanks!

 

[jtbell]

Right. It means that when you have a large number of boron atoms in a "natural" sample, 20% are one isotope and 80% are the other isotope.