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Published on August 7, 2009

Author: aSGuest23576

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Thin Layer Chromatography : Thin Layer Chromatography Forensic Analysis using Thin Layer Chromatography : Ink analysis Determines the specific chemicals Uses organic solvents Results are compared to a database of pen ink Forensic Analysis using Thin Layer Chromatography Forensic Analysis using Thin Layer Chromatography : Forensic Analysis using Thin Layer Chromatography Dye analysis Fibers Significant evidence Use thin layer chromatography to determine the different dyes in the fiber See how the colors elute Forensic Analysis using Thin Layer Chromatography : Pesticide analysis Pesticides are a hazard to the environment Many deaths are the results of poisoning from pesticides Pesticides are classified by their use or chemical type Determination of organophosphorus compounds in pesticide Forensic Analysis using Thin Layer Chromatography Forensic Analysis using Thin Layer Chromatography : Organic acid analysis Separation of carboxylic acids Organic acids are in textile, food preservatives, and medical agents Forensic Analysis using Thin Layer Chromatography TLC ProceduresPlate preparation : Mix the absorbent, water and a binder such as calcium sulfate Silica gel, paper and alumina Spread a thin layer of absorbent on an unreactive hard surface Glass, plastic, thick aluminum Heat in oven at 110°C for 30 mins to activate and dry the plate TLC ProceduresPlate preparation TLC Procedure : Place a small amount of solvent in a beaker In pencil, draw a straight line across the plate about 1 cm from the end of the plate Place a drop of sample solution on the line TLC Procedure TLC procedure : Add filter paper Place in solvent Sealed container TLC procedure How TLC works : How TLC works Sample solution is dissolved by solvent The solution sample will travel at different distances based on solubility, polarization, size Silica gel Polar substances do not move far Non polar substances move farther up the plate Calibration/Standards TLC : No calibration Standards Compare to other known substances Rf value Calibration/Standards TLC Solvents : Choose a solvent depending on the polarity of the compound Least Polar More polar Solvents Petroleum ether Cyclohexane Toluene Chloroform Acctone Ethanol Methanol Solvents : The solvent can be a mixture of compounds but the polar solvent properties will over take the non-polar one. 10-30% Methly tert-butyl ether, MTBE, in hexane, C6H14, works well 10-30% Methylene chloride, CH2Cl2, in hexane, C6H14, for a less polar mixture 10-30% Acetone, CH3COCH3, in Methylene chloride, CH2Cl2, for a more polar mixture Trial and error is the best way to approach which solvent to use. Solvents Visualization : Destructive visualization Spray plate with H2SO4, and then bake in the oven at 110ºC for 15-20 minutes. Compound is destroyed but all spots will be visible Nondestructive visualization – because of the use of a UV light the sample will not be destroyed. Although, not all of the spots on the plate will be visible. Long wave UV Short wave UV Semi-destructive visualization Visualization Visualization : Visualization A plate under a UV light to display the compounds after they were developed Interpretation : Interpretation Calculating the Rf value Calculate Rf Value : Calculate Rf Value Rf Value : The Rf value needs to be between 0.0 and 1.0 If the value is over 1.0 or less than 0.0, the calculation is wrong (you goofed) If the Rf value is greater than 0.8 or lower than 0.2 the values are hard to interpret, thus creating a larger error The best Rf values are 0.3 to 0.6 Rf Value Rf Value : The Rf value is not informative What affects the Rf value? Temperature Solvent Thickness and amount of spot Other compounds Rf Value Results : Multiple spots from one sample can be achieved. Results Pros for TLC : Sensitivity Speed Inexpensive Pros for TLC Cons for TLC : Too little of sample Too much of sample Subjective Cons for TLC

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