# Bainbridge Mass Spectrometer - Finding the mass of ions

• HollieDee
In summary, in a spectrometer, doubly ionised C and singly ionised Li atoms are detected with a ratio of path radii of 1.00252, with Li having the larger value. To find the mass of the lithium ion, an equation using velocity, charge on electron, magnetic field strength, and radii is used. By assuming the mass of carbon to be 12.011 amu, the mass of lithium is calculated to be 6.021 amu, slightly different from the accepted value of 6.941 amu.
HollieDee
In a particular spectrometer, doubly ionised C (atomic no. 6 mass no. 12) and singly ionised Li (atomic no. 3 mass no. 6) atoms are
detected. The ratio of the path radii is 1.00252, the Li having the larger value. The
fields are constant.

a)Find the mass of the lithium ion.

Okay so i have already figured out that i have to use the equation:

R=mV/qB (where m = mass, V = velocity, q= charge on electron, R= radius made by the ion and B= magnetic field strength)

I also have the equation:

q(1)R(1)/m(1) = q(2)R(2)/m(2)

(where the numbers in brackets are meant to be subscript)
This equation comes from knowing the value of V/B is constant.

so q(1)= 1.6x10^-19
q(2)= 3.2x10^-19
R(1)/R(2) = 1.00252

(R(1) being the radius of the lithium ion since it is stated to be the largest value)

This takes me to:

m(1)/m(2) = 0.50126

And this is where i get stuck! I can't see a way of doing this question without knowing the mass of carbon. I emailed my lecturer but all he said was 'The mass of carbon is implicit'.
Can anyone help? Thanks! :)

If your professor says that the mass of carbon is implicit, I suppose he means that it is 12.011 amu. This gives you a mass of lithium to be 6.021 amu, which is a little off from the accepted value of 6.941.

## 1. How does the Bainbridge Mass Spectrometer work?

The Bainbridge Mass Spectrometer works by ionizing a sample of molecules or atoms, separating them based on their mass-to-charge ratio, and then detecting and measuring the intensity of the resulting ion beams.

## 2. What is the purpose of using a mass spectrometer?

The mass spectrometer is used to determine the mass of ions present in a sample, which can provide information about the identity and structure of the molecules or atoms in the sample.

## 3. How does the mass spectrometer calculate the mass of ions?

The mass spectrometer uses a magnetic field to bend the ion beams based on their mass-to-charge ratio. The more massive ions will be deflected less than the lighter ions, allowing for their masses to be calculated.

## 4. Can the Bainbridge Mass Spectrometer be used for qualitative and quantitative analysis?

Yes, the Bainbridge Mass Spectrometer can be used for both qualitative and quantitative analysis. Qualitative analysis involves identifying the types of ions present in a sample, while quantitative analysis measures the relative amounts of each ion present.

## 5. What are the limitations of the Bainbridge Mass Spectrometer?

Some limitations of the Bainbridge Mass Spectrometer include its high cost and complexity, as well as the fact that it can only analyze ionizable compounds. It also requires a relatively small sample size and may not be suitable for analyzing large molecules or complex mixtures.

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