What I want to do

As we Know ,Spectroscopy is a very powerful technique for analytical chemistry, it help us to understand how light interacts with a certain compound or element allowing us to identify it, there are several types of spectroscopy, the most common one is visible spectroscopy which allows us to analyze in the visible range, (from 400-700 nm) this is good specially for colorimetric analysis and determination of the amount of analyte in solution, for element detection or specific compounds which emits/absorbs in visible light.., but one of the most important types of spectroscopy is infrared spectroscopy which works in the infrared region, infrared light is associated with vibrations, that’s why we usually associated infrared light with heat(thermal motion) , so let's go farther and lets imagine a molecule as a spring, this molecule is able to vibrate among the different bonds between atoms, some bonds are able to rotate , while others cannot depending on the electronic overlapping of the atoms that are bond to form the molecule, so let´s consider a vibration of atoms with respect to a certain bond, if a pulse of infrared radiation reaches the compound this vibration can be absorbed producing great variations on the infrared spectrum of the compound so we can conclude that infrared light is as a consequence the most cheap and non destructive analytical method that we can use to detect functional groups, and consequently to detect the presence of organic molecules among other analytes.The problem is that infrared spectroscopy instruments are extremely expensive , so the aim of this note would be to develop a powerfull but cheap spectroscope in order to be able to detect more infrared radiation than what we can detect with nowaday´s spectroscopes.

My attempt and results

As an example I want to show you two different solutions shown bellow, they are complete different from the chemical composition point of view, as you can see both interacts with the light in the same way in the visible range(both are blue). That´s meaning that they interact with photons in the visible range exactly in the same way, and as a consequence at our eyes they seem to be almost the same solution, so with visible spectroscopy we cannot notice any difference at all.

Let´s see now, the same solutions but with a near infrared camera which is able to see from 700-1000nm , a range that our eyes cannot see

As we can notice, one of the solution is black under the infrared , while the other is colorless, that´s indicating us that one solution is absorbing all the infrared light that is coming to the test tube and additional vibrations are produced, however the other solution cannot absorb the infrared radiation at this range so all of the photons between 700-1000 nm can pass trough it without been absorbed , remember that a photon is absorbed if its energy coincides with the difference in energy between two energetic levels involved in the electronic transition. In fact, the solution on the right is simply an aqueous solution of an organic dye, while the solution in the left is also an aqueous solution but in this case of an inorganic slat, cooper sulfate penta hydrated, when cooper sulfate is dissolved in water , it dissociates into Cu 2 + ions as well as sulfate ions, then the cation gets solvated and it´s surrounded by water molecules , this is what makes the solution blue, however cooper is a metal , and metallic solutions tend to block infrared light , that´s why it seem black under the infrared cam, while the other solution is colorless.

From a more technical point of view, the spectrum obtained for the transmitted light that passed through the solution is the following.

Blue plot represents the transmitted light of the solution that contains a blue dye

Red plot represents s the transmitted light of the solution that contains the copper sulfate aqueous solution.

As we can see form the picture both solutions interact with electromagnetic radiation in the same way in the visible range that´s why at our eyes they seem exactly the same solution, However above 700 nm more or less the cooper sulfate solution absorbs almost all the light in the infrared region , while the other solution transmitted almost all the radiation coming out from the bulb. That´s why infrared is so important for detection of functional groups.

The work range of this very simple device that I have designed is okay, but is not large enough to detect most of the functional groups present , the idea is to start a project to try to go farther and be able to look at lower frequencies, so we would be able to detect in the infrared range much more contaminants and chemicals in solution , than what we can do nowadays, It would be a nice idea a collaboration in between the spectroscopy and the infrared cam projects to try to achieve a camera able to detect more infrared light than what at the moment our cams are able to see.

As another example which for me is more interesting is the result that I have obtained when comparing chloroform and water, both are completely colorless, and in fact they behave almost equal at any wavelength, but I could notice a small difference in the infrared region.

If we magnify the infrared region we can even appreciate it better

This small difference would be enough to detect the presence of dangerous solvents in solution or other organic solvents , which would be very hard to identify with any other conventional technique

Questions and next steps

As future projects related with this one I would like to contribute with this research looking for more variations on the near infrared spectrum, of several compounds that I have available such as ketones , alcohols, esters and aldehydes and then compare it with the reference ( water) to try to stay if there is a significance difference in the spectrum or not in order to be able to detect a certain functional group in our problem solution.

It would be very nice as I have said a collaboration between the infrared cam project and the spectroscopy one to contribute to the design of a more sensitive instrument able to detect wider region of the infrared spectrum.

If you have any suggestion , comment or question please send me a comment or get in contact with me