Leaving me breathless - analysing your exhalation

Perhaps there are MOX-based gas sensors that could detect them, but I wouldn't necessarily trust them to be all that selective as cross-sensitivity is a known issue. Because these operate on a hotplate principle, their peak current consumption and size could be problematic.

- Gough

Here's a small device that does that: https://www.rkiinstruments.com/product/portable-gas-detector/

They measure :

Combustible Gases (Methane as standard)

Oxygen (O2)

Hydrogen Sulfide (H2S)

Carbon Monoxide (CO)

I checked the price. It's around $ 500.

As an alternative, we can check with Randall if a combination of these sensors would be up for a road test.

Or maybe a design challenge?

Mmm, doesn't appear to do NO (Nitric Oxide) ?

No. It can either do one of these combinations:

CH4, O2, NO2 (natrium dioxide) & CO or

CH4, O2, H2S & CO

Design Contest Time!

(contenders would need to have access to characterised samples of the gasses though)

I am very interested in your question, it has piqued my curiosity.

The first thing I have found is this NIOX VERO device

https://www.niox.com/

you may already know it.

It may provide a hint about possible sensors. It doesn't seem like an easy task for a portable device.

https://www.niox.com/en-cn/pdf/000247-08%20NIOX%20VERO%20Labeling%20summary%20EU.pdf

https://patentimages.storage.googleapis.com/cc/ba/05/34cc530da8549f/US10130284.pdf

https://patentimages.storage.googleapis.com/34/d3/8a/17634c08a84d00/US20110314896A1.pdf

The reference from javagoza is pretty useful.

Worth reading the operating manual which will give you an idea of just how difficult this is.

The usual sources sell NO sensors (eg Alphasense) but their parts have a 25 s response time which will be much too slow.

This is a good paper that talks about laser based mid IR detectors - good, fast but certainly not cheap.

https://coe.ou.edu/sserg/web/Publication/Papers/Nitric%20Oxide%20Breath%20Testing%20Using%20Tunable%20Diode%20Laser%20Ab…

What are you trying to make ?

MK

Thanks, I was not aware of the Niox, it looks like it's been assessed by NICE as well. Good thing I don't plan on making a device for the purpose of selling it.

michaelkellett

which will be much too slow

Could you explain what you mean?

This is a good paper that talks about laser based mid IR detectors - good, fast but certainly not cheap.

Aha, spectroscopy, that was a term that I kept grasping for when I was thinking about this. Thanks for the article.

Chemical sensors like the Alphasense have a time constant measured in seconds (25 in their case).

So a single breath won't be enough to get a good result.

Ideally for measuring exhalation gas you need to be able to make many measurements per breath.

So you need a sensor with a time constant more like 25ms - or tricky means of gas capture and storage while the sensor responds.

MK