A student researcher performed a chromatographic separation of caffeine and aspa
ID: 976838 • Letter: A
Question
A student researcher performed a chromatographic separation of caffeine and aspartame The retention time for caffeine, t_c, was found to be 201.3 s with a baseline peak width, w_c, of 15.7 s and the retention time for aspartame, t_a was 249.0 s with a baseline peak width, w_a, of 20.2 s. The retention time for the unretained solvent methanol was 48.0 s. Calculate the average plate height in micrometers for this separation, given that it was performed on a 29.3-cm long column. H= Number mu m Calculate the resolution, R, for this separation using the widths of the peaks R = Number Calculate the resolution if the number of theoretical plates were to increase by a factor of 2.5. R_2.5 N = NumberExplanation / Answer
Given that retention time for Caffeine ( tc) = 201.3s
Base line peak width (wc) = 15.7 s
The retention time for aspartame (ta) = 249.0s
Base line peak width (wa) = 20.2 s
Calculation for the average plate height:
The relationship between theoretical plate height ( H), the length of the column (L), the number of theoretical plates N was expressed as:
H = L/N
Length of the column = 29.3 cm;
In order to determine N, we can use the peak width at t(1/2), w(1/2); or the width at the base of the peak, w(b).
The formula for finding the number of theoretical plates is:
N = 16(ta/w(b))²
Plug in the numbers to get:
N = 16(249/20.2)²
= 199
on substituting these values in the above equation
H= 29.3/199 = 0.147 cm =1470micrometers
Calculation for the resolution (R) :
The resolution between the two is calculated from the formula:
R = t/w (avg)
t = 249 - 201.3
= 47.7 s
w(avg) = (20.2 + 15.7)/2
= 17.9 s
on substituting the values, we get
R = 47.7/17.9
= 2.66
C) The resolution is proportional to the square root of the number of theoretical plates. a 2.5 fold increase in resolution converts to a 6.25 fold increase in number of theoretical plates.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.