Thursday, February 10, 2005

Microwave and spectroscopes

In my continuing effort to show (to myself and my blodience) that I'm not a one-trick pony in science, this entry will be about Infra red spectroscopy and your microwave oven.

Electromagnetic radiation only has a few variable attributes by which it can be characterized. The fundamental particle of electromagnetic radiation is the photon, and the attributes are intensity, wavelength and polarization. Intensity is how bright the radiation is. If a large number of photons are coming from the source per unit time, we say it is a very bright source. Wavelength is related to the energy each photon carries. Photons with a very short wavelength each carry more energy than photons with a longer wavelength. The polarization of a photon refers to the direction the electromagnetic wave oscillates. If you've ever played with a broken pair of sunglasses, you've played with the polarization of electromagnetic radiation. We've given names to some of the different wavelengths that radiation can have. If the wavelength is about 700 nanometers, we call it red. If the wavelength is on the order of a meter, we call it a radio wave. If the wavelength is in the picometer range, it's a gamma ray or an x-ray. Infrared (IR) refers to any wavelength between 700 nm and 1,000,000 nm. The shorter wavelengths are called 'near IR' and the longer ones are called 'far IR'.

OK, but why is this useful? Well, These wavelengths correspond to the vibrations and rotations that molecules can undergo. Think about it: If a molecule is polarized, and it moves in space, say by turning around, or by oscillating back and forth, the magnitude and direction of the polarized portion will change. It will become an oscillating electrical field. This can interact with the oscillating electric field in a photon, if the oscillations can couple to one another. Every polar bond in a molecule is always vibrating at a frequency characteristic of the kind of bond it is. C-H bonds vibrate at a different frequency than C-O bonds, which are different from a C=O bond. Passing infrared radiation through a sample can help us determine what is in the sample based on what wavelengths of IR are absorbed. If the wavelength that corresponds to a C-O bond is very strongly absorbed by a sample, then we suspect that the sample has a C-O bond in it.

How does this relate to microwave ovens? Well, the microwave region of the electromagnetic spectrum is the region between IR and Radio waves, with wavelengths between 1 mm and 30 cm. Photons with wavelengths of about 12 cm correspond to the rotation of water. So, by irradiating your water-containing food with 12 cm radiation, all the water molecules in the food absorb the photons and increase in energy. Because they are excited, they bump up against other molecules in the food and excite them, and so on, until your food is hot.

Tuesday, February 08, 2005

Boring day in lab

Well, if I'm going to blog, I have to stick with it, even if it means pumping out crappy copy just to get into practice. Today I washed a lot of glassware. Woo woo. I also did some chromatography.

Today I sucessfully separated a three-component mixture into its parts with a silica gel chromatography column. The column consists of a vertical tube filled with silica gel (just like the silica in those little capsules in vitamin bottles that say "Do not eat") and hexane. The reason they put silica in vitamin bottles is related to the reason I put silica in my chromatography column. Silica is a very polar compond. It it also chemicaly inert, meaning it won't react under normal conditions. In the vitamin bottle, the silica acts as a dessicant, absorbing the water in the bottle to keep the vitamins dry. In my column, it acts as a stationary phase, and the hexane acts as a mobile phase. When I put my mixture onto the top of the column, and then allow more hexane to flow through the column, the parts of my mixture that are not very polar and soluble in the hexane will flow along with the hexane. Components that are more polar are less soluble in the hexane, and will tend to stay absorbed in the silica. The more hexane I pass through the column, the farther apart the components get, with the most polar ones hardly moving at all, and the least polar ones moving the farthest. The first few milliliters of hexane to emerge from the column contained all of my desired product, the second few milliliters contained the second component, but to get the third component off, I had to add a little methanol (a very polar solvent--more polar than the silica) to the column. Once I had evaporated the solvents, I had finally isolated my three compounds.

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