Monday, February 07, 2005

New idea: Mass Spectrometer. Pretty simple idea, the devil is in the details. A Mass spectrometer (or mass spec for short) will separate out atoms based on their mass. Steps involved:
1. Evaporate sample.
2. Ionize sample.
3. Separate out all ions save +1 charged ones.
4. Accelerate ions.
5. Subject ions to uniform and strong magnetic field.
6. F=qvB, where q=charge, B=magnetic field strength, v=velocity. F=mv^2/r. Heavier ions will deflect less in the field.
7. Measure ions (by current, charge, impact, whatever).

I know some mass specs measure different masses by varying the field strength to sweep the ions by a single detector. A linear CCD (or other long detector) would be able to pick up multiple ions at once.

Measuring current seems too sensitive--can I measure nanoAmps? I know better the response of CCDs than anything else. But these are big particles that won't go far into the detector, and might get stuck in the control gates atop the silicon.

I wonder if I can get more sensitive results by increasing the length of the device. If the ions are deflected by say 0.1 degrees per amu, but I can't see that, I could lengthen the travel distance and they would separate out further on the detector.

Vacuum--a problem since I have no experience.

Can I build a miniuature mass spec using a new technology magnet (i.e., hard drive magnet)?


colin said...

Measuring current seems too sensitive--can I measure nanoAmps?Perhaps you could run the current through a resistor? The DVMs the physics department uses for all the teaching labs are pretty basic, and they'll easily pick up microVolts. Maybe even nanoVolts, I can't remember. All you would need is a resistor of no more than kiloOhms.

colin said...

How big are those hard drive magnets? AS&S has some pretty gnarly magnets, though I'm not sure if they're as powerful as the ones in hard drives. Or if the added strength is worth the cost.

Dean W. Armstrong said...

Physically big? They are 2 to 3 mm thick, approximately 2 x 1 cm. In the hard drive they come in pairs, so if you keep the pair together, you get a doubly strong field that I think is normal to the surface of the magnet. The other side of the magnet is kept with a large steel piece. I believe the strongest one I have is roughly 1 Tesla.

Anonymous said...

This type of mass spec has been in use for some time called a magnetic sector instrument. They used large electromagnets to vary the field strength.