Re: [DIYbio] Vacuum pumps and smell?

On Thu, Oct 2, 2014 at 9:34 AM, Alex <spider87@gmail.com> wrote:

http://www.phonearena.com/news/Breakthrough-sensor-to-give-our-smartphones-a-sense-of-smell_id48089

I know very little about vacuum pumps but I don't understand how a vacuum pump can smell something. Is there some inherent feature of vacuum pumps that allow them to detect smell?

You are correct in being confused, a vacuum pump can't inherently smell something. In the research presented, they made a pump which can create 'rough vacuum', which is the stage when the majority of a gaseous mixture is still compressed, and a simple fan can remove molecules... up until the point that the gasses are pretty much fully expanded, so 'suction' speed of the pump is limited to diffusion speeds (while before the low pressure created by the fan was allowing the gas to expand which provided the fan with molecules to push).

After the rough vacuum is achieved, the pump isn't much use, as it's effectiveness is countered by how leaky it's seals are... that is when you'd flip the switch on a turbo molecular pump... essentially a turbocharger from a car running in reverse, with really really good seals. This pump is still pretty much a fan, but it goes so fast that it pumps faster than it leaks, allowing the pressure in the vacuum chamber to drop even more.

When you get to this medium vacuum level, you then have to turn on an ion trap, which adsorbs the floating gas molecules (very few in the chamber at this point) or uses high-voltage to ionize and then electroplate the gas to a metal plate.

Only at this super molecule-free level of vacuum do you start to do things in it, like electron microscopy, ion milling, or mass spectrometry.

Because mass spec first ionizes a sample, bends that beam of ions with a magnetic field (ever put a charged balloon near a running water faucet and saw the stream of water deflect, or place a magnet on the side of a CRT TV?)  and finally through a selection slit... any ions or other floating molecules (gas) will get in the way of your analyte and mess up your detected signal (your analyte broken into fragments then separated by mass and the amount of that species quantified).

But again, the research presented in that doc, and the linked docs, talk only about the first stage, the roughing pump. They would still need to figure out how to miniaturize the turbo pump, though the ion trap should be less difficult.

One of the major challenges is taking a prototype MEMS device to production scales. One-off devices might be possible today, in the size and package desired, but they might take a long time to make and cost a lot. Figuring out how to streamline that process can be quite difficult.

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