Essay, Research Paper: Chromatography Research

Chromatography Research
Most likely, the average person off the street couldn't tell you exactly what chromatography is. I, however, can tell you this, and much more relating to the subject. Chromatography is defined by Webster's Dictionary as "a process in which a chemical mixture carried by a liquid or gas is separated into components as a result of differential distribution of the solutes as they flow around or over a stationary liquid or solid phase." Not all mixtures can be separated using any one form of chromatography, so various methods have been developed over the years. The most commonly used forms of chromatography are column, high performance liquid, ion, paper, thin layer, and gas chromatography. By separating the individual components of different mixtures, scientists are able to study the components much easier and more efficiently. In 1906, Russian botanist Mikhail Tswett became the discoverer of chromatography when he poured a petroleum-ether extract of green leaves over a column of powdered calcium carbonate in a vertical glass tube. By doing this he was able to separate each of the pigments and thus study each in depth. It wasn't until the 1930's that chromatography became widely used in the scientific community, but as its popularity increased, discoveries abounded.
Column chromatography is one of the more common forms of chromatography because it can be used for very delicate separations that are hard to achieve using other methods. For this method, a vertical glass or plastic tube, (usually 50 cm tall and 1 cm wide) is packed with a stationary phase such as aluminum oxide or calcium carbonate. Then the mixture to be separated is dissolved in a solvent and added to the top of the column where it (the mobile phase) will then work its way down and separate into its different components. In high performance liquid chromatography, the particle size of the stationary phase is greatly reduced in order to increase surface area and thus allow for better separations. The catch is that the process becomes far too timely for most applications. In order to overcome this, highly sophisticated pumps are used to propel the mobile phase through the stationary phase that is typically in a glass tube 1 - 5 mm wide and 10 - 30 cm long. In ion chromatography, a column is packed with an ion exchange resin that has ions weakly attached to it. As the mobile phase passes over the resin, the weakly bonded ions are displaced by the ions in the mixture with a stronger attraction to the resin. The ions with the strongest attraction bond closer to the top of the column and the weaker bonding ions are found at the bottom of the column. As the name suggests, paper chromatography takes place on paper rather than in a tube. Drops of the solution to be separated are placed on strips of paper located in closed containers in which the atmosphere is saturated with water vapor or solvent vapor. One end of the strip in then placed in a dish of solvent and the solvent moves through the paper separating the mixture as it goes. The separations are usually viewed as colored spots on the paper. Thin layer chromatography takes place on a glass or plastic plate that is coated with a very thin layer of stationary phase. Just as in paper chromatography, a drop of the mixture to be separated is placed on the medium that is in an atmosphere of solvent vapor. The rest works just like paper chromatography. The final type of chromatography to be discussed is gas chromatography. In this method, an inert gas is used to carry the mixture to be separated through an apparatus that has many tubes that are coated with a liquid that gradually adsorb various components of the mixture to various degrees. Each component then passes through a tube fitted with an electrocouple that measures the current produced by different amounts of the separated substances mixed with the inert gas. A computer then interprets the information obtained.
Chromatography has become a very valuable tool for scientists and the affects of its employment are felt by nearly everyone. For example, by using gas chromatography, the over 100 individual compounds found in gasoline can be separated out and studied to provide us with car engines that are more efficient and last longer. People that live in places where "hard water" is a problem can get rid of their "soap scum" by using water softeners that operate on the basic principles of chromatography. Also, the agricultural runoff of farms can be separated using chromatography in order to see whether or not harmful chemicals are making their way into places they shouldn't. Chromatography can even be used to test for drug use among athletes. The list of uses goes on and on.
One way to learn about chromatography in a high school lab is to form our own glass columns to use in column chromatography. This way we would feel more in touch with the columns and thus we would be more careful and our result would be more accurate. Another way would be if someone happened to donate some rather expensive thin layer chromatography plates for the AH and AP chemistry classes to use. We could separate all sorts of the things from various kinds of ink, to blood, to foods and beverages. As far as my personal feelings for chromatography are concerned, I think its swell! Honestly, having the power to separate a mixture containing hundreds of different microscopic components is pretty incredible. What can I say, chemistry rules.