A chromatogram of a mixture of ethanol, 1-propanol, and 1-butanol was obtained W

Question

A chromatogram of a mixture of ethanol, 1-propanol, and 1-butanol was obtained Wid a 6 foot column at a flow rate of 30.0 cm3/min. The recorder chart speed was 1.00 in/min. Calculate the adjusted retention time (t) for ethanol, propanol, and butanol, the resolution (R) between the ethanol and propanol peaks, the height equivalent of a theoretical plate (H) for propanol, and the relative retention (a) of butanol with respect to ethanol. Compound Distance from injection, in Peak Width, in air ethanol 1-propanol 1-butanol 0.50 1.50 2.25 3.10 0.25 0.30 0.40

Explanation / Answer

Solving for the height equivalent of a theoretical plate for propanol.

Height equivalent of a theoretical plate H = L/N

where L = length of column

N = number of theoretical plates

Now, L = 6 foot = 72 inches

N = 5.545 (tR/W)2

where tR = retention time = distance from injection point to propanol peak / chart speed

tR = 2.25 in / 1.00 in min-1 = 2.25 min

W (propanol) = 0.30 in

therefore, N = 5.545 (2.25/0.30)2 = 312

H = L/N = 72/312 = 0.234

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