A peak elutes from an HPLC column 118cm in length in 138 min

A peak elutes from an HPLC column 11.8-cm in length in 13.8 min. What would be the width at half-height of the peak (in seconds) if the plate height were:

(a) 6.9 m?     (b) 36 m?

Solution

no of plates = length of column/(height of plate)

= 11.8 cm /( 6.9*10^-4 cm = 17101

W1/2 = sqrt ( 5.55*13.8^2)/17101) = 0.249 min = 15 sec

b)

no of plates = length of column/(height of plate)

= 11.8 cm /( 36*10^-4 cm = 3278

W1/2 = sqrt ( 5.55*13.8^2)/3278) = 0.568 min = 34 sec