Download Determination of Caffeine Extraction Profile in Brewing Coffee: A Lab Experiment and more Study notes Analytical Chemistry in PDF only on Docsity! CHEM 212; Lab 7 1 Determination of the Caffeine Extraction Profile of Brewing Coffee Before lab: 1. Write a procedure for the preparation of a 1000 ppm caffeine stock solution 2. Calculate the volumes needed to dilute the 1000 ppm caffeine stock solution in order to achieve 0, 100, 250, 400, and 500 ppm standards 3. Write a procedure similar to the examples shown below describing what you want to do. Introduction: When coffee or tea is prepared, hot water is used to extract flavor components and other molecules, such as caffeine are also extracted caffeine. Caffeine (1,3,7-‐trimethylxanthine, FM= 194.19g) is slightly soluble in water and is a central nervous system stimulant with a bioavailability of 99% (CRC and wikipedia). The onset of action is typically 45 minutes and the typical half-‐life inside the body is 3-‐7 hours. Typical caffeine concentration in beverages and common foodstuffs is shown in Table 0-‐2 (Harris, 2005). The purpose of this lab is to experimentally determine the caffeine extraction profile (a plot of mass of caffeine extracted versus time) for the brewing of caffeinated beverages. You will develop your own procedure to determine caffeine concentration for the brewing or steeping profile of your beverage of choice. After sample collection, concentration of caffeine will be detected and quantified using High-‐ Performance Liquid Chromatography (HPLC). The HPLC is used to separate the components of samples, in this case coffee or tea, into individual components using a chromatographic column. These individual components are detected using a UV-‐Visible spectrophotometer or mass spectrometer. The UV-‐Visible spectrum of caffeine shows substantial absorbance at 272 nm. The molar absorptivity at 274 nm is approximately 2 x 104 L mol-‐1 cm-‐1 in ethanol solution. This wavelength is monitored and the caffeine standard demonstrates a retention time of 7.3 minutes (Fig. 1). The mass spectrometry detector also detects caffeine at 7.3 minutes and shows a distinctive mass spectrum pattern (Fig. 2). In actual samples, the matrix is more complex, this results in a more complicated chromatogram. The mass spectrometry and UV-‐Visible chromatograms are different, since the UV-‐Vis chromatogram results for analyte molecule absorbance at 272 nm while the mass spectrometry chromatogram counts the total number of CHEM 212; Lab 7 2 analyte ions reaching the detector as a function of time. Figure 1: Total ion count chromatogram and mass spectrum of the caffeine standard as detected by the mass spec detector. Figure 2: Total ion count chromatogram and mass spectrum of the caffeine standard as detected by the mass spec detector. Procedure: Be creative! You can examine the caffeine extraction profile for anything (coffee, espresso, tea, whatever) with a caffeine content that will change as a function of time within 15 or so minutes. If you need specialized equipment or supplies (tea, coffee, etc) you need to bring them with you to lab. If you bring your own coffee maker or similar we will perform the experiment outside lab to prevent contamination. Complete procedures will include: 1. Brewing or steeping conditions (volume of solution, mass of coffee or tea, temperature of water, etc). 0 200 400 600 800 1000 0 2 4 6 8 10 In te ns ity )me (min)
