The following questions apply to separation of a solution containing pentanol (F

Question

The following questions apply to separation of a solution containing pentanol (FM 88.15) and 2,3-dimethyl-2-butanol (FM 102.17). Pentanol is the internal standard.(a) Separation of a standard solution containing 231 mg of pentanol and 259 mg of 2,3-dimethyl-2-butanol in 10.0 mL of solution led to a pentanol:2,3-dimethyl-2-butanol relative peak area ratio of 0.909:1.00. Calculate the response factor, F, for 2,3-dimethyl-2-butanol.

(b) Calculate the areas for pentanol and 2,3-dimethyl-2-butanol gas chromatogram peaks in an unknown. For pentanol, the peak height was 61.5 mm and the width at half-height was 3.0 mm. For 2,3-dimethyl-2-butanol, the peak height was 79.6 mm and the width at half-height was 3.5 mm. Assume each peak to be a Gaussian.

(c) If the concentration of pentanol in the unknown solution of part (b) was 73.9 mM, what was the 2,3-dimethyl-2-butanol concentration?

Explanation / Answer

(a) molarity of 2,3-dimethyl-3-butanol in solution = 0.259 g/102.17 g/mol x 0.01 L = 0.25 M

molarity of pentanol (std) in solution = 0.231 g/88.15 g/mol x 0.01 L = 0.26 M

response factor for 2,3-dimethyl-2-butanol = (1/0.909) x 0.26 = 0.286

(b) Area for pentanol = 61.5 mm x 3 mm = 184.5 mm^2

Area for 2,3-dimethyl-2-butanol = 79.6 mm x 3.5 mm = 278.6 mm^2

(c) If the concentration of pentanol = 73.9 mM

concentration of 2,3-dimethyl-2-butanol = (61.5/79.6) x 73.9 = 57.10 mM

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