The Hive > Serious Chemistry
automating production: the use of home-made monochromatic spectrophotometers? -drone
PolytheneSam:
Here's something interesting. This was in an electronics catalog that I got in the mail. Notice it says that the 'optical' bandwidth is 7-14 µm. The most important part of the 'chemical' IR region in the IR spectrum is between 2 and about 15 or 16 µm (in the mid IR region). The first IR spectrophotometers typically had that bandwidth. Later ones went up (down in energy) to 25 µm. There's some that even work in the far and/or near IR region. The near IR region is between visible light and the mid IR region and the far IR region is between the mid IR region and the microwave region. The detector costs $3.25 for one and $2.59 for 10 or more. Not too long ago I had some conversations over the phone with someone that works at a company that repairs lab equipment including IR specs. He said that he sells used and repaired IR specs starting at $3,000 and would sell me an untested one (no guarantee) for $500. He also said sometimes detectors go bad and old ones cost at least $1000, but he did mention that lower cost solid state detectors exist and also emphasized that you can't take parts from one spec and use then in another. In my opinion you can if you know enough electronics to do the modifications to make it work. Typical detectors are based on vacuum thermopiles, bolometers, etc. and don't work on the photoelectric effect. From my extensive reading on the subject as well as studying physics, I don't think practical photoelectric detectors exist (even today) for the mid IR region which would work over the whole region. I've searched through the patents and on the internet and found IR detectors which are made using similar methods for making integrated circuits (chips) but these use vacuum thermopiles, too. The thermopiles are etched in the silicon along with any other electronics. The cost is lower that an older type of thermopile detector. So, I think this might be a vacuum thermopile type detector here.
http://www.geocities.com/dritte123/PSPF.html
PolytheneSam:
Here's something else I started working on. http://www.geocities.com/apis_mellifica2002/IRramble.html
Two main differences between visible and IR spectrophotometers is that visible light covers a region that is less than a factor of 2 in wavelength and visible light photons have a higher energy than IR photons. E = hf where E = energy of the photon, h is Plank's constant and f is frequency of the photon. Energy reaching the detector in typical IR prism and grating spectrophotometers is in the microwatt range. Also, the fact the the 2-16 or the 2-25 µm range is more than a factor of 2 means that spectral orders from the grating overlap and require filters or a prism to seperate them. Visible light covers 450-700 nm.
nm = 10 -9 meters
µm = 10 -6 meters
http://www.geocities.com/dritte123/PSPF.html
terbium:
I always hated trying to interpret IR spectra, far too ambiguous for me. NMR spectra are so much nicer. Does anyone have ideas on how to build a (hydrogen) NMR spectrometer for, say, less than a $1000 ?
Osmium:
Well, I don't think you tried to imply that Sam, but I say it anyway so that nobody gets the wrong ideas:
It is highly doubtful that a $3 IR detector will work in a IR spectrometer, since it lacks in linearity, sensitivity, resolution etc.
> Does anyone have ideas on how to build a (hydrogen) NMR
> spectrometer for, say, less than a $1000 ?
No way.
I have seen tabletop models (which apparently recorded F or P NMR spectra), but for a proton NMR you need a huge electrical magnet capable of producing a very uniform magnetic field of high strenght. Building these isn't trivial at all!.
While data processing can be done by an old Pentium, there is the transmitter/receiver problem. Let's say you go for a 60MHz device, then you need a way to detect the shifts, which will just be several Hz (ppm!). Not an easy sunday afternoon task.
Greensnake:
Homebuilt NMR... ouch. Well, electronics is not that much complicated (if you are good with RF stuff that is) but not the faintest idea how to even start making NMR grade magnet at home. Probably the best course would be finding old 60 mhz NMR gear and outfitting it with new brains. There was an article in not so old (few years max) Journal of Chemical Education about how to do this. I do have a copy but unfortunately - buried somewhere VERY deep in my papers.
Greensnake
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