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PostPosted: Mar 21st, '12, 18:10 
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Charlie wrote:
Infrared (IR) spectroscopy is one of the most common spectroscopic techniques used by organic and inorganic chemists. Simply, it is the absorption measurement of different IR frequencies by a sample positioned in the path of an IR beam. The main goal of IR spectroscopic analysis is to determine the chemical functional groups in the sample. Different functional groups absorb characteristic frequencies of IR radiation. Using various sampling accessories, IR spectrometers can accept a wide range of sam- ple types such as gases, liquids, and solids. Thus, IR spectroscopy is an important and popular tool for structural elucidation and compound identification.

IR Frequency Range and Spectrum=
Infrared radiation spans a section of the electromagnetic spectrum having wavenumbers from roughly 13,000 to 10 cm–1, or wavelengths from 0.78 to 1000 μm. It is bound by the red end of the visible region at high frequencies and the microwave region at low frequencies.
IR absorption positions are generally presented as either wavenumbers ( ν ) or wavelengths (λ). Wavenumber defines the number of waves per unit length. Thus, wavenumbers are directly proportion- al to frequency, as well as the energy of the IR absorption. The wavenumber unit (cm–1, reciprocal cen- timeter) is more commonly used in modern IR instruments that are linear in the cm–1 scale. In the contrast, wavelengths are inversely proportional to frequencies and their associated energy. At present, the recommended unit of wavelength is μm (micrometers), but μ (micron) is used in some older litera- ture. Wavenumbers and wavelengths can be interconverted using the following equation:

–1 1 4 ν (in cm ) = ------------ × 10
IR absorption information is generally presented in the form of a spectrum with wavelength or wavenumber as the x-axis and absorption intensity or percent transmittance as the y-axis


Did that make me look smart? serious cut and paste expert!!
It makes no sense to me whatsoever :-P



It did...untill you posted the last bit :)

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PostPosted: Mar 21st, '12, 21:28 
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Dam... note to self - too honest. :oops:

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PostPosted: Mar 21st, '12, 23:10 
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Just make it a general policy in future to leave out the last line of your posts.

It's

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PostPosted: Mar 22nd, '12, 05:44 
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rsevs3 wrote:
Will you need nitrate initially? You could calibrate with distilled water and the just work on the detection of each chemical. After that work on concentrations.


I don't think of the calibration of the spectroscope , yes, i think the distilled water is enough .to the spectral calibration.
I think we need the chemicals, because we have to make a calibration line to each chemicals.
It isn't all the same, what kind of light source used...i think, it deform the place of the absorptions in the spectrum.

So we need to make a calibration line from the dilution series, with a light source, and save the light intensity (on on the characteristic wavelength of the chemical) that belong the concentration.
and if we use the same light source, and want to measure an unknown concentrated chemical, we can measure the light intensity on the characteristic wavelength of the chemical, and we can search that on the calibration line, so we can define the concentration, that belong to the light intensity (on the characteristic wavelength of the chemical).

Or am i wrong?

Quote:
Some of the links i posted previously had the spectrum for each chemical


where? i didnt find the spectrum of the chemicals like nitrate, and ammonia etc.
Although i'm usually deconcentrated :)

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PostPosted: Mar 22nd, '12, 11:45 
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When we saw graphs earlier, were they plots of thousands values of different frequencies of light absorbed (or reflected) at varying amounts depending on what was in the sample?

Is that how this stuff works?

If so, isnt it just a case of finding what a dose of ammonia does to your graph, and writing a few lines of code that say something like..

If any wavelengths between ABitToTheLeftOfAmmonia and ABitToTheRightOfAmonia are greater than SomeUpperLimit then SoundAnAlarm

Given the general stability of a mature system, I wouldn't think there would be any real need for great accuracy in identifying the exact compound, (or the exact values) as long as ammonia is included in that little group of compounds you check for. Especially if the stuff on either side of ammonia (on your graph) are things that we don't have to worry about (uranium or helium or something).

Am I making sense?

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PostPosted: Mar 22nd, '12, 15:01 
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That is close to my thinking too BW. Just have a system to tell if they are there and then progress to concentration.

Katonafull, my thinking from what i have read is this. As long as your light source emits at the required frequencies, to just prove the presence of chemicals, you wont need to 'find' the lines. They should be the same no matter what light source you use. You can calibrate your individual webcam with any known chemical to ensure the accuracy of the measured spectrum. Spectoral-Workbench uses the 2 mercury lines. I am guessing this should be sufficient for what we are trying to achieve. The spectrums for each chemical is linked to in the following website:

http://publiclaboratory.org/wiki/video-spectrometer

This is one of the files it links to which at a quick glance i can see ammonia (NH3)

http://archive.publiclaboratory.org/hitran-spectral-library/By-Molecule/ByMolecule-Readme.pdf

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PostPosted: Mar 23rd, '12, 22:53 
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Wow, I go away for a couple of weeks and you guys finish the race without me :)
Excellent progress!

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PostPosted: Mar 24th, '12, 05:57 
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I was wondering where you got too :)

Certainly havent finished the race yet. Barely begun it me thinks :think:

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PostPosted: Mar 24th, '12, 23:59 
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My new webcamspectroscope :)

http://spectralworkbench.org/spectra/show/164


Attachments:
type to label next spectrum.png
type to label next spectrum.png [ 55.77 KiB | Viewed 1845 times ]

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PostPosted: Mar 25th, '12, 04:53 
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It is quite interesting to see the difference between your light and mine. I really do have to put mine back together and test it again. Yours is far more like what i would expect to see from a fluro. Awesome stuff. :)

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PostPosted: Mar 25th, '12, 07:39 
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I know this has nothing to do with anything but i figured the people who would find this interesting keep an eye on this thread.

http://www.wired.co.uk/news/archive/2012-03/09/230-percent-efficient-leds

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PostPosted: Mar 26th, '12, 03:40 
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rsevs3 wrote:
That is close to my thinking too BW. Just have a system to tell if they are there and then progress to concentration.


Ok, but how would you define the concentration of an unknown sample without a calibration line?
May the concentration is not linear with the intensity of the absorbtion line,
or the function between the absorption and intensity isn't begin in the origo.


Quote:
It is quite interesting to see the difference between your light and mine. I really do have to put mine back together and test it again. Yours is far more like what i would expect to see from a fluro. Awesome stuff.


it is a spectra of a very cheap fluro...

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PostPosted: Mar 26th, '12, 04:48 
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You are correct katonafull. I was just suggesting that i think it would be a good idea to work on detection first and then worry about concentration. Just knowing that the chemical is there or not will be a big enough challenge by itself i think.

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PostPosted: Mar 26th, '12, 09:55 
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rsevs3 wrote:
You are correct katonafull. I was just suggesting that i think it would be a good idea to work on detection first and then worry about concentration. Just knowing that the chemical is there or not will be a big enough challenge by itself i think.



And perhaps all that's required for an aquaponics monitor.

Concentrations are not particularly important for a chemical that should read zero. I realize there will always be some ammonia in a system, but if you create a device that outputs some numbers in a healthy system as tested by a chemical kit, reset all the numbers to zero, then any spike of any kind is a problem.

The chemical tests work fine with only 6-8 different points of reference, but for me, the important one for nitrites and ammonia is simply that there is some.

Once you have some values, it might be possible to just test against know concentrations as discovered by a chemical test kit, check it with the spectroscope, then just call whatever value the spectroscope says the same level that the test kit shows. Then add some more ammonia or whatever, test again, etc etc.

That way you have a result without having to know what the numbers really mean, which as I understand it should mean you can do it with any light source as long as it casts a spectrum at the relevant points of interest.


Perhaps I'm missing something. I often find that that's the case :)

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PostPosted: Mar 26th, '12, 10:23 
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rsevs3 wrote:
I know this has nothing to do with anything but i figured the people who would find this interesting keep an eye on this thread.

http://www.wired.co.uk/news/archive/2012-03/09/230-percent-efficient-leds


That is a very nice piece of kit.

I think that means they have found an entirely new way of cooling as well. If you took it a little further, you could make a thermalvoltaic cell, or use it as a heat pump to move heat by converting it into light then move it around through fibre optics, and turn it back into heat at the end.

Or just squirt it outside where it belongs on a hot day.

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