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Unformatted text preview: Slope, m = 7.958 b intercept = 108..9 (Vs)0 =-13.69 L March 17, 2011 CHEM 4128 Measuring the Concentration of Caffeine in Dr. Pepper through HPLC/UV Objective Liquid chromatography can be used on compounds that are not volatile enough to be brought into the gas phase such as larger, biologically relevant molecules or ionic compounds. Separation in liquid Chromatography is based on polarity but in this experiment we will use reversed phase LC, which means the stationary phase is non-polar and the mobile phase is polar (Normal phase is with a polar stationary and a non-polar mobile phase). In this method, the more non-polar compounds will be increasingly retained, thus lengthening their retention time. An isocratic elution will be used in this experiment, meaning there will only be one solvent mixture used as an eluent. The column used in LC (as opposed to GC) is a relatively short, wider bore steel tube filled with fine particles on which the stationary phase is chemically bonded. There are also pumps that move the eluent through the column and a detector that is a UV absorbance spectrophotometer. The purpose of this experiment is to measure the concentration of caffeine (C 8 H 10 N 4 O) present in Dr. Pepper and to gain better knowledge of liquid chromatography in quantitative analytical chemistry through the use of standard addition. Experiment To begin the experiment, ~13 mL (suppose to be 25 mL, mistakes will be discussed in the conclusion section) of Dr. Pepper was measured out in a beaker and 1 pellet of baker analyzed NaOH was added and dissolved. Once dissolved, the pH was checked to insure it was 8 or greater. 5 mL of the basic sample was transferred into an extraction vial and 1 mL of methylene...
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