Question

A chromatogram gives an ideal Gaussian peak with tr = 9.80 min and w1/2 = 0.17 min. How many theoretical plates does the column have? N = plates What is the plate height of the column in millimeters if the column is 10.8 cm long? H =

Answer 1

Column efficiency defined as the number of theoretical plates per column, and number of theoretical plates can be obtained from a chromatogram from the expression

N = 5.54 (t_R / w_0.5)² where t_R is the retention time of the analyte and w_0.5 the width of the peak at half height.

given t_r = 9.8 min

w_0.5=0.17 min

N= 5.54t_r/w_0.5)²

N=5.54(9.8/0.17)²

N= 5.54*57.65²

N = 18412 plates

the height equivalent to a theoretical plate H is the length of column L divided by the number of theoretical plate N.the unit is cm per plate

H= L/N

H=10.8 cm/18412

H =5.86*10^-4 cm

H =5.86*10^-4  *10 =5.86*10^-3 mm =0.00586 mm [1 cm =10 mm]