Studyguide2 - Study guide for exam 2 This exam will cover spectroscopy chromatography HPLC GC Mass spectrometry 1 Example questions and objectives

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Study guide for exam 2: This exam will cover spectroscopy, chromatography, HPLC, GC, Mass spectrometry 1. Example questions and objectives for each chapters are must-know 2. In a particular assay, the absorbance reading on the spectrophotometer for one sample is 2.60 and for another one 0.03. Would you trust and use them for quantitation purpose? Why or why not? Answer is on page 378 of text book. The 2.60 is too high and the 0.03 is too low for reliable quantitation. The ideal range is 0.1-0.9. 3. If a compound can be measured using either UV/vis spectroscopy or Fluorescent spectroscopy, what would you choose? What are the advantages of fluorescent spectroscopy over the UV/vis spectroscopy? 4. Chlorophyll A has a uv/vis spectrum like this. Can you determine its λ max ? What wavelength would you use to determine chlorophyll A content on a spectrophotometer? 5. At 520 nm, if 70% of light transmit through a cuvette and 30% of light is absorbed by the solution in the cuvette, please calculate transmittance T% and absorbance A. % T = 70% A = log(1/T) = 0.155 6. a) The absorbance of 3x10 -5 M cyanidin solution in a 0.5-cm cuvette at 520 nm is A=0.44, please calculate its molar extinction coefficient? Molar extinction coefficient ε = A/(bxc) = 0.44/(0.5x3x10 -5 ) = 0.29 x10 -5 cm -1 M -1 b) The molar mass of delphinidin is 303 g/mole. You are requested to measure its content in a grape juice. One milliliter of grape juices is mixed with 9 mL of water. Measured A=0.43 using a standard 1-cm cuvette. The molar extinction coefficient of delphinidin is 5.34 x 10 5 . Please calculate the content of delphinidin in this grape juice in mmole/L or mg/L. c = A/( εxb) = 0.43/(5.34 x 10 5 x 1) = 0.805 x 10 -6 mole/L 10 x c = 8.05 x 10 -6 mole/L = 8.05 x 10 -3 mmole/L 8.05 x 10 -6 mole/L x 303 g/mole = 2439 x 10 -6 g/L = 2439 x 10 -3 mg/L = 2.439 mg/L
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7. At what circumstance would you consider using standard addition for quantitation? 8.
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Studyguide2 - Study guide for exam 2 This exam will cover spectroscopy chromatography HPLC GC Mass spectrometry 1 Example questions and objectives

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