A student researcher performed a chromatographic separation of caffeine and aspartame. The retention time for caffeine, tc, was found to be 204.6 s with a baseline peak width, wc, of 14.7 s. The retention time for aspartame, ta, was 266.2 s with a baseline peak width, wa, of 19.9 s. The retention time for the unretained solvent methanol was 45.7 s. Calculate the average plate height, H, in micrometers for this separation, given that it was performed on a 26.5 cm long column. H = Calculate the resolution, R, for this separation using the widths of the peaks. R = Calculate the resolution if the number of theoretical plates were to increase by a factor of 2. R2N =
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5 cm = 26.5 * 10 mm = 265 mm N = 3312 H = (265 / 3312) * 10000 **H = 80.01 μm** ** Show more…
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Peak Retention Time (minutes) Peak Width, 4σ (minutes) 1 0.85 0.15 2 2.75 0.20 3 5.5 0.50 Analytes (alphabetical order) Acetonitrile H3C-C≡N Benzoic acid Caffeine Given the above data calculate: a) Time spent by peaks 1, 2, 3 in the stationary phase and in the mobile phase. b) Resolution between peaks 2 and 3, c) Sketch the chromatogram of these species. Indicate which peak would most likely correspond to each analyte (reverse phase HPLC, isocratic elution, pH=3). If necessary, state how to make the separation better. d) Calculate the partition equilibrium constant for peak 3, assuming Vm/Vs= 10
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Listed below are retention times and peak widths for an HPLC chromatographic separation on a 10 cm C18 column: a) Calculate the resolution between benzene and benzo[e]pyrene. Compound Time (min) Baseline Width (min) Unretained 0.9 - Benzene 10.9 0.40 Benzo[e]pyrene 13.3 0.40 Pyrene 16.7 0.45 Coronene 26.1 0.50 b) Is this a good resolution, yes, no, why? c) Calculate the theoretical number of plates for benzo[e]pyrene.
(a) When a 0.235 -g sample of benzoic acid is combusted in a bomb calorimeter (Figure 5.19$)$ , the temperature rises $1.642^{\circ} \mathrm{C} .$ When a $0.265-\mathrm{g}$ sample of caffeine, $\mathrm{C}_{8} \mathrm{H}_{10} \mathrm{N}_{4} \mathrm{O}_{2}$ is burned, the temperature rises $1.525^{\circ} \mathrm{C} .$ Using the value 26.38 $\mathrm{kJ} / \mathrm{g}$ for the heat of combustion of benzoic acid, calculate the heat of combustion per mole of caffeine at constant volume. (b) Assuming that there is an uncertainty of $0.002^{\circ} \mathrm{C}$ in each temperature reading and that the masses of samples are measured to $0.001 \mathrm{g},$ what is the estimated uncertainty in the value calculated for the heat of combustion per mole of caffeine?
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