Crime and Dye Lab Essay

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 Procedure * Phosphorescence Two different polyaromatic acids, 1- naphthoic acid and 4-biphenylcarboxylic acid, were obtained and drops were added unto two filter paper. The solvents heated to dryness for 11 minutes using a hot plate on low heat. The filter papers were then placed under long and short wavelength ultraviolet lamps. Observation of the intensity and duration of glow were recorded. * Fluorescence Tonic water was poured into a beaker. Long and short wavelength UV lamp was shined above the beaker. Observations were recorded. Now, a beaker of water was taking to the UV lamp and was shined at the beaker. Observations were recorded. After, 3 drops of concentrated fluorescein solution was added into the beaker. The UV lamp was shined above the beaker and observations were recorded. * Chemiluminescence 2 mL of Tekrakis-(dimethylaminoethylene) was added into a small test tube. This test tube was taken to the UV lamp and shined at. Observations about the intensity and duration of glow were recorded. After, 1 mL of luminol in DMSO was added into five test tubes. Now, in each test tube fluorescein, rhodamine, rubrene and perylene solutions were added in 4 four of the five test tubes. Observation of the color of each solution was recorded. At this point, 1M NaOH was added into each test tube and was then shined with a UV lamp. Further observations were recorded. Finally 1 g of Al2O3 was added into four 250 mL Erlenmeyer flask. This was mixed with 1 mL of 3% H2O2. In each flask, perylene, tetracene (2,3-benanthracene), 9,10-Dipehenylanthracene, and rubrene were added respectively. Now, 1 mL of oxalic chloride was added in each flask and swirled. Observations were then recorded. * Crime Lab A water bath was heated and maintained at 650C. Now, scribbles were made on papers from each of the four pens. The paper with each scribble was cut into small pieces and placed into a marked test tube. Also, a scribble of an unknown pen was obtained. The paper was also cut into small pieces and placed in a test tube. 2 mL of methanol was added into each test tube and was placed in the hot bath for 5 minutes. The test tubes were allowed to cool, the color of the inks were recorded and poured into five cuvettes. Using a UV-Vis spectrophotometer, the wavelength peaks and absorbance of each ink solution were recorded. Four of the five dyes were then poured into new marked test tubes. The solutions were then boiled for 14 minutes until the there were less than 1 mL. The solutions were allowed to cool. Now, a 250 mL beaker was obtained. In it was added a small amount of methanol (less than half a centimeter in height). A filter paper was then obtained and cut towards the end (B.1). This was placed at the side of the beaker. Finally, an alumna plate was cut in the dimension of 8 x 4 cm. A line was drawn at a 1 cm height using a pencil. In this line, drops of the four inks were spotted. This plate was then leaned inside the end of the beaker (B.2). The plate was left in the solvent until it reached  ¾ of the way up. The height the inks and solvent reached up the plate was recorded.