Has anybody built their own mass spectrometer before?

[ikrase]

The abysmal resolution comment referred solely to 200 dollar pipe tee spectrometers.

The quadrupole has a few notable advantages. One is that the ion source collimating requirements are less.

I thought that the quadrupole was velocity invariant.

[Someone]

Magnetic sector mass specs were the first to be invented iirc. They are not as popular for several reasons, but the bulkiness of the magnets doesn't help.

Pipe tee MS is very cheap, uses only neodymium magnets, but has abysmal range and resolution.

I think the biggest expenses are the vacuum system and the ion source as long as no electron multipliers are used.

Low resolution Hmmm. It is a given that the quad pole is much better for finely separating the masses with high resolution. The question in my mind is why. Or for that matter why is a magnetic separator low resolution. The magnet separator has a the advantage of not being effected by ion velocity. The quad system does not have this advantage. One would think that this in itself would give the magnetic separator an advantage. Apparently not as the quad pole is producing the best results.

If you do just a little reading:
https://en.wikipedia.org/wiki/Triple_quadrupole_mass_spectrometer
The TQMS is typically associated with molecular work, and magnetic sectors are able to practically produce much higher resolution and are still the go-to for most isotopic work.

[John Heath]

The abysmal resolution comment referred solely to 200 dollar pipe tee spectrometers.

The quadrupole has a few notable advantages. One is that the ion source collimating requirements are less.

I thought that the quadrupole was velocity invariant.

The only reason I said the quadrupole is not velocity invariant has to do with the difference between using a magnetic field  VS an electric field to move an ion. With a magnetic field the movement is always the same as the faster the speed the greater the magnetic deflection. The two cancel out. However with an electric field such as the quadrupole the greater the ion speed the less the deflection. There could be other variables going on in the quadurpole that compensate for this?

200 dollar pipe tee soectrometer. This peaked my interest. Is there a cheap 200 dollar spectrometer out there? For 200 bucks it does not have to be good.   

[LaserSteve]

So I get back from vacation and find myself looking at dynodes for another project.  The simplest ones are made of BeCu sheets processed in a furnace with water or other vapors to favor making a very thin layer of  BeO instead of CuOx  on the surface.  These have a gain of "12" if made correctly for electrons.

Beryllium Copper sheet is common enough..

Steve

[ikrase]

Beryllium Copper? Innnnteresting. I shall have to investigate that someday. Requires high temperature tolerant bonding and an atmospheric furnace but no more.


There is indeed another variable in quadrupoles. It is true that by themselves, static magnetic fields are velocity-invariant and electric fields are not. However, in a quadrupole, what matters isn't the magnitude of any deflection, but whether the vibrating path the particles take through the quadrupole is stable or not.

(Quadrupoles, and other 2N-poles, can be tuned so as to pass a wide range of M/Z ratios, in which case they actually serve as a guide or "pipe" for moderate-velocity charged particles.)

Obviously, a particle that is way too fast will just punch through the quadrupole without being really affected, and the percentage of wrong-mass particles that 'leak' through will be higher with a high velocity-to-quadrupole-length ratio, but it's mostly just a matter of the quadrupole being long enough.

[LaserSteve]

Evidently how you clean and process the surface before the furnace step matters.  Yes,  you can get your Dynode Blanks at nearly any specialty sheet metal place and  especially at your favorite overnight, in stock, industrial MRO supplier with headquarters outside  Chicago.

Steve