Use the following data for questions 8-10. Coffee is commonly analyzed with reve

Question

Use the following data for questions 8-10. Coffee is commonly analyzed with reverse-phase HPLC to determine the concentrations of caffeine, theobromine, and theophylline. The following chromatogram was obtained from standards of these materials (Figure taken from J Chrom. Sci. 2002, 40,45) 2 Peak Retention (min) solvent 1 -theobromine 7.89 2 - theophylline 8.14 3 - caffeine 5.87 12.76 3 12 16 Time (min) 8. From the figure, calculate selectivity (relative retention) between theobromine-theophylline and theophylline-caffeine Your answer 9. From the figure, calculate the resolution between each set of adjacent peaks in the chromatogram (that is, between theobromine-theophylline and theophylline- caffeine) when the column is rated at an efficiency of 7550 theoretical plates

Explanation / Answer

9. From the above shown chart

Using,

Resolution (R)

R = (retention time for IInd peak - retention time for Ist peak)/1/2(sum of width of two peaks)

For,

theobromine-theophylline

R = (8.14 - 7.89)/1/2(1)

    = 0.5

For,

theophyline-caffeine

R = (12.76 - 8.14)/1/2(3+0.5)

    = 2.64

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