Crime and Dye Lab
Special Projects 1
Light is usually viewed as a result of the heating of a substance. The higher the temperature at which the substance is heated, the greater the vibrations that lead to certain light intensity given off by the molecule. It is this same theory that suggests why steel glows red hot when heated to high enough temperatures. The process of light emissions can also be induces through other means. 1
One of such means termed fluorescence occurs when a substance can be induced into giving off light is through absorption of a photon through light or other means of radiations. During this process, electrons are excited from their standard state. The electrons jump from their highest unoccupied orbital (HUMO) into a certain level of the unoccupied orbital (LUMO). As the electrons loose energy, they fall back to a lower orbital, thus emitting light. 1, 2
During the process leading to fluorescence, a certain change could occur during the excitation of the electron, changing the spin of the electron as it gets excited. This change has to be undone as the electron goes back to its standard state. The emitting of light in this process is known as phosphorescence. The process of fluorescence is much faster than phosphorescence. This is due to the fact that in phosphorescence, the electron has to undergo an extra step of undoing its current spin. This process is thermodynamically unfavorable compared to fluorescence. 1, 2
The last means by which light could be generated is through chemiluminescence. In such a case a chemical reaction occurs, causing an excitation of the product. As this product decays into its standard state, light is emitted. This form of luminescent is different from the previous two in the sense that no absorption of light is required to induce the glow. The glow results from the product of the chemical reaction having to be in an exited state or of higher energy. 1
The process of photon absorption and emission is certain a phenomenon that plays a vital role in our society. Such importance is expressed during rescue operations, where victims can be easily found due to waving of a fluorescent material at night. It is evident that fluorescence becomes important when a thermally induced light emission is deemed impossible. 1, 2
Separation techniques were concepts that were important in the course of this experiment. One of such is through the means of UV Vis Spectrophotometer. The constituents of ink dyes can be determined using a spectrophotometer. By placing the dyes in the spec, various wavelength peaks will be obtained. These peaks can be used to find out the constituent colors making up the dye.
Another important form of separation used during this experiment is chromatography. Chromatography utilizes the differences in polarity of substances as means of separation. Such is the case of a crime lab involving the finding of a pen used in writing on a piece of paper. If a pen out of four is used to write a note, the particular pen can be detected using chromatography. The dyes of all four inks and the unknown ink can be obtained. This ink can be run through a chromatograph column, allowing a solvent to run above the ink dyes, carrying them along. After a certain point the RF values of all the inks can be used to detect the particular ink. The RF value is the distance the ink travels divided by the distance travelled by the solvent. The ink with the same RF value as the unknown is the same ink used. Chromatography has a wide range of use. It use can be stretched from this as it can also be used to indicate the component amino acids found in various proteins. The protein can be run through the column, resulting in the various amino acids that make the protein, to be separated. 1, 2
Materials and Methods (Summarized from Lab Manual) 1
Two different polyaromatic acids, 1-...