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I saw that there has been a push to make a drug detector that can identify cannabis since it has been legalized. I was looking at mouser.com and found this ir sensor: https://www.mouser.com/ProductDetail/Pyreos/PY2435?qs=sGAEpiMZZMvkSJWT1okH7HZM1X5NjtfhYufzstUzGmFpPHtO%2FKJ1pA%3D%3D I also found these IR spectra enter image description here enter image description here

The ir sensor has filters for 8550nm(1169cm^-1), 8750nm(1143cm^-1), 9650nm (1036cm^-1), 12250nm (816cm^-1). Also your typical methane detector is at 3300nm(3000cm^-1) so alot of these line up with the absorbance peaks, do you think this will work as a detector? I have seen typically for organic compounds that have aromatic rings or pi bonds UV spectroscopy is typically used but i cant seem to find UV detectors online. Is there an easier way to do this? What is a good estimate of ppm that this ir detector could sense?

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  • \$\begingroup\$ Sorry, but I think I might have missed the whole electronics/electrical engineering part of your question, could you narrow it down? Like, are you asking for types of sensors that could detect particles in gasses? \$\endgroup\$ – jDAQ Jan 5 '20 at 0:00
  • \$\begingroup\$ boselec.com/products/sic-uv-photodiodes or boselec.com/product-category/… \$\endgroup\$ – Tony Stewart EE75 Jan 5 '20 at 0:05
  • \$\begingroup\$ have you considered the false-positive problem? \$\endgroup\$ – Jasen Jan 5 '20 at 0:12
  • \$\begingroup\$ @jDAQ yes i was asking for whether you thought the following sensors would work to sense drug particles in the air. \$\endgroup\$ – ChemEng Jan 5 '20 at 0:59
  • \$\begingroup\$ @Jasen yes i understand that there might be a false positive problem but there are 4 sensors at 4 different wavelengths in just one sensor and if i bought 2 that would be 8 different sample wavelengths so i thought it may be possible even if they do not allow for custom filters to get the most appropriate wavelength \$\endgroup\$ – ChemEng Jan 5 '20 at 1:00
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The ir sensor has filters for 8550nm(1169cm^-1), 8750nm(1143cm^-1), 9650nm (1036cm^-1), 12250nm (816cm^-1). Also your typical methane detector is at 3300nm(3000cm^-1) so alot of these line up with the absorbance peaks, do you think this will work as a detector?

That detector is meant for measuring the concentration of a known gas in a purified form. It works because the measurement is of a known, purified substance. You need to define both the substance you want to detect and the additional substances you want to be able to exclude. That determines which and how many wavelengths are needed.

I have seen typically for organic compounds that have aromatic rings or pi bonds UV spectroscopy is typically used but i cant seem to find UV detectors online.

There are a lot of companies that sell UV spectrometers online.

What is a good estimate of ppm that this ir detector could sense?

The range of PPM that could be detected depends on the instrument using the detector. With a large volume, ultra-pure sample, and long integration time, you could measure parts per billion or even smaller. With an impure sample, you won't be able to measure at all.

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  • \$\begingroup\$ These 4 in one sensors are made for measuring 3 different gasses in one sensor typically they are carbon monoxide(4.64um), carbon dioxide(4.26um), methane(3.3um) and reference(3.91um). Here you can see someone using a carbon dioxide sensor just in normal air just by blowing on it with his breath youtu.be/inVmjXzm2zk . I think you guys are WAYYYYY overestimating the limitations \$\endgroup\$ – ChemEng Jan 5 '20 at 19:34
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with only four measurements such a sensor will only be able to detect pure THC, there will be 4 innocuous substances that when mixed will confound the measure sufficiently that detection of trace amounts of THC will not be possible.

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I think you will have an issue with false positives because of the overlap peaks with other compounds. Depending on what your tolerance specifications for false positives might be, you may prefer a more accurate method. Why reinvent the wheel, nature has already supplied us with a quite accurate specific compound detection method; canine olfactory detection. Customs and Border authorities have used this method for many years and very reliable. I don't think you can improve on it with these sensors.

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  • \$\begingroup\$ yes but most people dont own a dog \$\endgroup\$ – ChemEng Jan 5 '20 at 1:24

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