Consider the data below for a liquid chromatography separation of four compounds

Question

Consider the data below for a liquid chromatography separation of four compounds, A, B, C, and D on a 45.0 cm column. Calculate the number of theoretical plates, N for each peak Retention Time (min)Base (min) Width at the A 5.09 12.7 14.1 0.445 1.01 1.19 1.95 Number Number N-2448.62 Nc 2405.26 Number Number N2529 2241.73 Incorrect Calculate the number of theoretical plates, N, for each compound using the equation shown to the right, where& is the retention time and wis the width of the peak base. N-16 N 240635 What is the plate height, H, for the column? Number H 110.0 187 cm

Explanation / Answer

Number of theoretical plates

N = 16 (t/w)2

t = retention time

w = width of peak base

For peak A

NA = 16 x (5.09/0.445)2

= 2093.32

For peak B

NB = 16 (12.7/1.01)2

= 2529.79

For peak C

NC = 16 (14.1/1.19)2

= 2246.28

For peak D

ND = 16 (23.3/1.95)2

= 2284.35

Navg = (NA + NB + NC + ND) / 4

= ( 2093.32 +2529.79 + 2246.28 + 2284.35) / 4

= 2288.44

Plate height = column length / Navg

= 45 cm / 2288.44

= 0.01966 cm

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