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Analytical Wavelength • Unique for each sample • Determined by intercepting an absorbance spectrum • Wavelength at which a sample absorbs the most light Process 1. Calibrate the spectrophotometer. 2. Determine the analytical wavelength for the blue, red, yellow food dye 3. Remember to use clean pipettes so samples are not contaminated Determine the Analytical Wavelength 1. Using a pipet, transfer water and each of the color dye solutions to a cuvette. Then wipe the cuvettes. 2. Place the cuvette of water into the spectrophotometer, “zoom in” on the screen, and choose calibrate instrument. 3. Place the cuvette with a color dye solution into the spectrophotometer and zoom in on the screen 4. Select the “Full Spectrum” Analysis Mode. 5. Move the cursor to the peak of the graph and find the maximum absorbance. Record the wavelength associated with the maximum absorbance in your Notebook. 6. For each of the remaining two color dye solutions, determine the analytical wavelength and enter it to your Notebook. Calibration Curve • At a given wavelength, Beer’s Law predicts a linear relationship between the absorbance of a light absorbing portion of a substance (chromophore) and its concentration. • A calibration or standard curve is a graph representing this relationship with absorbance on the y-axis and concentration on the x-axis. • The slope of the line provides the product el, where e is the molar absorptivity coefficient and l is the path length in cm. Which of the following will affect the value of the molar absorptivity coefficient (e)? a. Changing the concentration of the chromophore b. Changing the wavelength at which the measurement is made c. Changing the path length (l) of the cell d. Changing the identity of the chromophore When using spectrophotometry, to determine the concentration of a chromophore in a sample, transmittance values between 0.15and 0.65 produce the smallest relative errors in concentration determinations. Which of the following terms is a measure of the amount of light that is absorbed by a solution? a. Molar absorptivity coefficient

b. Absorbance c. Transmittance d. Intensity Which of the following terms describes a graph of the absorbance of a solution versus the wavelength of light oassing through the solution?...