How Does a Mass Spectrometer Calculate Ion Path Radius?

In summary: I am not familiar with the specific system and its capabilities. Perhaps double-check your calculations to make sure everything is correct.
  • #1
TbbZz
37
0

Homework Statement


Consider the mass spectrometer shown schematically in Figure 19.30 (don't have a scanner so I can't put the picture). The electric field between the plates of the velocity selector is 950 V/m, and the magnetic fields in both the velocity selector and the defelection chamber have magnitudes of 0.930 T. Calculate the radius of the path in the system for a singly charged ion with mass m = 2.18x10^-26kg.

Homework Equations



I'm not sure what to do with the 950 V/m. I also do not know whether a "singly charged ion" means it is a proton or an electron.

The Attempt at a Solution



I have attempted to try to find out where I use 950 V/m and what a "singly charged ion" means. I don't think I can go any further without knowing those two pieces of information. I'm not trying to ask for the answer (I've spent 1 hour on this question and I'm willing to spend as much time as it will take to answer it), I just don't know where to start.

Thanks. :smile:
 
Last edited:
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  • #2
They give you the mass of the particle. Also, this is a mass spectrometer so the ion is positive.

Now you simply need to calculate the velocity of the particles that get through the velocity selector, right? These particles are undeflected by the B and E fields, so the force due to the B-field is equal to the force due to the E field. Or, qVB = qE. or, v = E/B. Take the ratio of the E and B fields given to find the velocity.

Now, you know the centripetal force due to the B-field acting on the mass when it passes into the curved tube is F = qVB = mv^2/r, right? You know q, V, B, and m, so you can easily find r.

"singly charged" simply means that the charge of the ion is the same as the charge of an electron (but positive).
 
  • #3
Also, notice why the velocity selector is a crucial component of the spectrometer?
 
  • #4
Thank you very much leright for the quick and informative response.

Why is the Electric Field given in V/m instead of N/C though?

Plugging 950 in for the E/B ratio gets me around 1021m/s for the velocity, which seems really low for this type of situation.
 
  • #5
TbbZz said:
Thank you very much leright for the quick and informative response.

Why is the Electric Field given in V/m instead of N/C though?

Plugging 950 in for the E/B ratio gets me around 1021m/s for the velocity, which seems really low for this type of situation.

Both V/m and N/C are suitable units for electric field.

Regarding the accuracy of the velocity, I am not sure...
 

Related to How Does a Mass Spectrometer Calculate Ion Path Radius?

1. What is a mass spectrometer?

A mass spectrometer is a scientific instrument used to measure the masses and relative concentrations of atoms and molecules in a sample. It works by ionizing the sample, separating the ions based on their mass-to-charge ratio, and detecting the resulting signals.

2. How does a mass spectrometer work?

A mass spectrometer works by first ionizing a sample, which means it converts the atoms or molecules into positively or negatively charged ions. These ions are then accelerated through an electric field and passed through a magnetic field, which causes them to separate based on their mass-to-charge ratio. The separated ions are then detected by a detector, usually a photomultiplier or electron multiplier, and the resulting signal is converted into a mass spectrum.

3. What is the purpose of a mass spectrometer?

The main purpose of a mass spectrometer is to analyze the composition of a sample by determining the masses and relative concentrations of its components. It is commonly used in fields such as chemistry, biochemistry, and environmental science to identify and quantify substances such as proteins, drugs, pollutants, and environmental contaminants.

4. What are the different types of mass spectrometers?

There are several types of mass spectrometers, including time-of-flight (TOF), quadrupole, magnetic sector, and ion trap. Each type has its own advantages and applications, but they all work based on the same principle of ionization, separation, and detection.

5. How is a mass spectrometer calibrated?

A mass spectrometer is typically calibrated by analyzing known standards of different masses and plotting a calibration curve. This curve is then used to convert the detected signals into mass values. Some mass spectrometers also have internal calibration systems, such as a laser or a reference compound, to ensure accurate mass measurements.

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